Waiting to Tell an Epic Tale

The Roxbury Conglomerate waited to tell its story 20 feet from where I played with my son and visited with friends at Martin Hilltop Playground in Dorchester, Massachusetts.  Rocks have a way of doing that; waiting that is. Parts of this outcrop had survived 650 million years, traveled thousands of miles and climbed probably two or three to tell an epic tale of rises and falls, separation and unification. And it was only on my way out of the park that I took the time to glimpse the gray layered rock with walnut sized chunks of white , gray and pink stone trapped within.  Each type of smaller stone told part of what it took to get this rock to a park near the south edge of Boston.

The story of these rocks begins not far from the coast of Africa.  A light colored rock with largish crystals called granodiorite indicates a fond farewell from Africa.  The dense rock that forms much of the ocean's bottom is jet black, and we call it basalt. When a new ocean tears a continent open, that basalt forming magma wends through lighter colored continent rock, forming a kind of salt and pepper blend of the two called diorite.  Chunks of the Dedham Granodiorite (an even lighter version of diorite) within the conglomerate may have formed in a prePangea split. As this island fragment of Africa set off on its own, erosion and sorting would have created new sediments. Another type of fragment, the gray Westboro Quartzite, thought to have a similar age as the Dedham rock, may have been a beach on the coast of this diverging island. The beach would have been transposed to sandstone and eventually quartzite with time and travel.  Each of these rocks, encapsulated in the conglomerate is a chapter in the conglomerate's story.

Breaking from its roots in Africa was only one small step in Avalon's eager journey to become part of North America.  After all, the ocean is not only wide; it's firm.  Unlike the water that overlies it, the bottom of the ocean is solid stone. Once Africa split, an ocean bottom's worth of material, like so much yellow shag carpet, would need to be removed to make way for Avalon's trip. But, where to put it? A convenient choice might be underneath the very crust of the Earth itself. As the continent moved west to escape Africa and join America, the ocean in its path was shoved below (in a process called subduction). This arrangement only works so well, however. Less dense ocean bottom material has trouble sinking through denser mantle (the layer of the Earth beneath its crust), and post-descent some of the slab melts and floats upward. When this melted rock makes its way to the surface, we call it a volcano. Thus was born the reddish  Mattapan Volcanics, another component of the Roxbury Conglomerate.

The large chunks of rock contained within tell their own individual parts of the story, but the conglomerate itself reveals the denouement.  Imagine standing in stagnant water, your feet squelch in the muddy bottom. In a stream, or wavy coast, mud is hustled away and what remains is sand. Speed that stream up by, say, running it through a set of miles-high  mountains, and your feet rest on well worn gravel.  All but the biggest chunks of the mountains above have been dragged well out to sea by a raging river.  How do you get mile high mountains made of an amalgam of granodiorite formed deep in a splitting continent, quartzite formed on shoreline, and volcanic rock formed in migrating islands?  You crush the whole, complicated, landscape in the binding vice of Africa and North America as they form one corner of the supercontinent Pangea.  The mountains climb, and the gravel falls.

The intervening couple of hundred million years is mostly waiting for the conglomerate and its components. Waiting to harden from riverbed into stone. Waiting for the giant mountains to be worn down to roots. Waiting while glaciers scour the rock and sediment above. Waiting for Boston and the park to be built. Biding time for the opportunity to tell an epic tale to curious visitors. Don't worry, the rocks don't mind the wait.


Hepburn, Christopher J., Javier Fernandez-Suarez, George A. Jenner, and Elena A. Belousova. "Significance of Detrital Zircon Ages from the Westboro Quartzite, Avalon Terrane, Eastern Massachusetts." Geological Society of America 40.2 (2008): n. pag. Web.

Reid, Annie. "Nature Notes 5/12/2006 - A Mighty Collision and Much Glaciation." The Westborough News. Westborough Community Land Trust, 12 May 2016. Web. 06 July 2016

Watts, Douglas. "Geology of North Easton, Massachusetts: We're Still in West Africa." Tispaquin's Revenge. N.p., 6 Feb. 2010. Web. 06 July 2016.

 Thompson, Margaret D., and O. Don Hermes. "Ash-flow Stratigraphy in the Mattapan Volcanic Complex, Greater Boston, Massachusetts." Geology of the Composite Avalon Terrane of Southern New England Geological Society of America Special Papers 245 (1990): 85-96. Web.

Everybody's Got to Eat

Life will do anything for energy. On the mid slope trail of Portland's Eastern Promenade the ruddy, oily mess that surrounded me made that abundantly clear. This particular portion looks like the effluent pond of a pre-Clean Water Act chemical plant. In one direction water seeps out of the ground, somewhere between the color of blood and orange finger paint. In another, a rich, rainbow sheen texturizes the look of a shallow pool, bringing to mind the "Dump No Waste, Drains to Lake" stencils that pop up around water bodies. Despite the look, I know better. I've seen similar scenes in Acadia National Park, an area protected and remote enough that dumping just doesn't seem worth it, even for the most villainous human polluters.  Bacteria, however, are another story.

When you get hungry, you might grab an apple and chow down. Your body tears apart the weak bonds of the apple's sugars, leaving a soup of carbon, hydrogen and oxygen atoms. These atoms don't like the single life and when your lungs immerse them in a bath of even more oxygen, the hungry oxygen atoms snap up carbon and hydrogen to create your two favorite molecules: Carbon dioxide and water. You might think it's the sugar that gives you the energy, but, really, your energy comes from building the strong bonds in the compounds you exhale.

The polluters on the East End work the same way: they take up weakly bonded or unbonded atoms and snap them into strong bonds to create energy. Of course their chemical soup is completely different than yours and mine. Instead of carbons and hydrogens, they take up the fourth most common element in the Earth's crust: iron.  Like carbon and hydrogen, iron isn't a big fan of going it alone, but deep underground there isn't much of a selection of partners. But, as ground water flows to the surface, it drags with it lonely iron ions, inviting them to a chemical party that they wouldn't have had access to in the subterranean world.  Up here, oxygen is a near perfect mate. The bacteria are the E-Harmony  of the chemical world, speeding up the matchmaking process and reaping the energy benefits when sparks fly. When oxygen joins with iron, the strong bonds snapping shut powers the life of the bacteria.  Like you and I exhale carbon dioxide and water, bacteria pumps out these red-orange iron oxygen compounds, called iron oxides.

That explains the red seeps, but what about the oil on the water's surface?  It's worth thinking about what oil is.  Generally, oil is the leftover parts of simple organisms that lived a long time ago. In a way, the oily sheen is donated by a material not too different than the fossil fuel. Bacteria, including those that metabolize iron, have a short lifespan. The creation of iron oxides provides the energy needed to power more and more of this simple life form. When members of the community die, their parts float on the surface. The surface film of broken up bacteria creates the same rainbow effect as their prehistoric counterparts that form petroleum.

These iron bacteria may have an impact on our visual environment.  But it's not fair to call them polluters.  They're just trying to live the same way they have for almost a billion years.  To do that means eating, breathing and dying, just like you and me.

Clark, M. S. (2015, October 16). What is Oil? Retrieved April 16, 2016, from http://www.sjvgeology.org/oil/oil.html

Ilbert, M., & Bonnefoy, V. (2013). Insight into the evolution of the iron oxidation pathways. Biochimica Et Biophysica Acta (BBA) - Bioenergetics, 1827(2), 161-175. doi:10.1016/j.bbabio.2012.10.001

Wartinbee, D. (2010, March 24). Science of the Seasons: Yellow boy bacteria has people seeing red. Retrieved April 16, 2016, from https://redoubtreporter.wordpress.com/2010/03/24/science-of-the-seasons-yellow-boy-bacteria-has-people-seeing-red/

Through the Past and into the Future: A View from the Harpswell Cliffs

The cliff walk in Harpswell lives up to its name. The trail makes a turn and dumps you out on a view worth far more than the effort required to hike to it. While it didn't take me long to reach the top of the 150 foot cliff, the rock itself would have taken far longer to make the climb. The rock is schist - the glittery remains of mudstone that has been crushed and baked in Earth's oven. The mud itself piled up in some prehistoric ocean bottom, perhaps at a rate of a foot every thousand years. Peering down the 150 foot cliff to the estuary below, I imagined a stream tediously cutting through millennia worth of deposition, time traveling further and further into history. This erosion might open a window into a time period 150,000 years before the rocks on which I stood formed. As it turns out the chasm was a portal through time, but the time machine traveled into the future.

Around 490 million years ago, a slab of continent we call Avalon near the South Pole cleaved itself from its parent, a supercontinent called Gondwana.  As it journeyed northward it developed a predictable series of layers.  An early layer became our cliff. Not long after it left the Antarctic Circle mud rained down on the ocean floors of the microcontinent's coast. It accumulated for that 150 thousand years and longer.  As the microcontinent scrolled past 40 South, 445 million years ago, volcanoes laid new rock on top of old. This was, in turn, buried by ocean bottom. The new ocean floor was topped by one final, explosive, volcanic eruption, the icing on a layer cake of rock that was a testament to the long journey. 

A lot went on to make the Harpswell Cliffs time portal.
First the layers of rock were laid down flat (with the
schist of the cliffs in blue and the volcanic rock across
the estuary in red).  Then the layers cracked and stacked.
Next they bent into wavy layers.  Finally the tops were shaved
off by erosion, exposing our cliffs and the peninsula below.

In an orderly world, where progress is constant, it is obvious that the rocks of the Antarctic circle would never be seen again. Instead they would be buried deeper and deeper. But these rocks lived in a world where journeys end. The unstoppable northward force would eventually meet its harbor, the immovable North American continent. This collision was massive. Pieces of continent were flung and tumbled, like ice onto a spring shore.  Avalon cracked and its parts were thrust on top of one another.  Now it was that final explosive eruption, the icing on the cake, that had been interred by its own past.

The compression of this part of the Earth continued. The heat and pressure of the collision would transmogrify the fine grained mudstones into glittery schists. The layers would flex into a washboard of ridges that make southern Maine's coastal islands and peninsulas so multitudinous, lifting the schist of those cliffs to their present height and higher.  The problem was that gravity abhors a ridge. Ice, water and good old falling did their best to even off the tops of the rolling ridges. Sanding of those tops meant revealing the bowed edges of the cake layers.  

It may have been a glacial flood, a stream funneled by a weak layer of rock, or just plain luck that cut through those last 150 feet. Whatever it was gave me a window through one hundred and fifty thousand years of mud to a blue estuary below. Looking across the water revealed not a predictable past, where time moves ever forward. Instead, I looked into an explosive future where, given enough time, the world could be turned upside down.

Liu, Dennis. Earthviewer. Computer software. Vers. 1.1. Howard Hughes Medical Institute, Jan. 2013. Web. 11 Apr. 2015

Hussey, Arthur M., and Henry N. Berry. Bedrock Geology of the Bath 1:100,000 Map Sheet, Coastal Maine. Augusta, Me.: Maine Geological Survey, Dept. of Conservation, 2002. Print.

Druyan, Ann, and Steven Soter. "The Clean Room." Cosmos: A Spacetime Odyssey. Fox. 20 Apr. 2014. Television.

Say Goodbye to Graptolites...

Graptolite fossils from Presque Isle

It's hard to get sentimental about graptolites. The fossil of what's actually a colony of tiny animals looks more like a small saw blade than anything you might start a preservation campaign for.  It's probably for the better, too. A successful "Save the Graptolites" crusade would have preserved a world where reptiles and pine trees would never have thrived. In Silurian era Presque Isle, however there would have been no need to improve conditions for graptolites. They were already perfect.  

In a low outcrop not far from downtown Presque Isle, the pale rock feels gritty, but not coarse. This type of sediment is not the product of a deep ocean or a beach, but the sweet spot in between.  It's born in an area where prevailing winds could blow off the warm top layers of an ocean, and reveal the cold nutrient rich waters below.  Perhaps inconsequential to you or me, but life changing to a graptolite.

Certain shards of the rock slab host the shallow impressions of graptolite rhabdosomes, basically an apartment building for tiny animals called zooids.  In Silurian time the complexes either rooted themselves in coastal sediment or floated in masses at the surface.  The zooids may have reached out of the many holes in these colonial homes to grasp at and eat phytoplankton from the coastal waters, enriched by the upwelling of vital nutrients.  

In a time when Caribbean-like islands stood sentry on the coast of North America habitats like this would have been commonplace in Maine. But, Maine was changing. Three hundred eighty million years ago the tectonic block that serves as our current coast, Avalon, docked with Maine. The conjunction crumpled the graptolites' ocean habitat.  Driving fossil types of graptolites from fourteen  in the Silurian to one after the collision. Eighty million years later the jaws of Pangea snapped shut.  The huge landmass was inhospitable to the aquatic creature and by the time it had formed the graptolites were extinct.

The watery Silurian period was ideal for graptolites. The changing environment drove them out of Maine, and then to extinction.  A sad moment, perhaps. But, the transition to dry land had some advantages, too.  Plants left the coasts, invading Pangea, and in the process became trees. Amphibians bravely abandoned their shrinking watery habitats and evolved into reptiles. Graptolites didn't make it, but maybe that's okay. Perhaps their loss is our gain.

Dickson, Lisa, and Robert D. Tucker. Maine's Fossil Record: The Paleozoic. Augusta, ME: Maine Geological Survey, Dept. of Conservation, 2007. Print. 

Koren', T. N., and R. B. Rickards. "Extinction of the Graptolites." Geological Society, London, Special Publications (1979): 457-66.

"Graptolites." Common Fossils of Oklahoma. Sam Noble Museum. Web. 20 Dec. 2014.

The Long View: Half a Billion Years in the County



The view from State Street in Presque Isle

This August I spent a week in mythic Aroostook County.  Throughout my week there I navigated rolling hills and potato fields, marched to the top of Quaggy Jo in Aroostook State Park and summited Haystack Mountain in Mapleton. The county is a geological wonderland, but it wasn't until I crested that hill in Presque Isle that I recognized the magic of the place.



The view of Haystack Mountain from State Street in Presque Isle

Traveling down State Street into Presque Isle, you turn a corner, the road dips downward, and you look across the county at Haystack Mountain. That rock has been on Earth for half a billion years.  Once the neck of an ancient volcanic island, the Aleutian-like island gained girth as the North American ocean bottom slid under a second ocean plate. The lightest of the melted ocean rock floated to the surface forming the steep-sided stratovolcano that would one day become the western view from Presque Isle.

The view of Quaggy Jo from State Street in Presque Isle

If you're not completely transfixed by Haystack, your eyes may wander south as you pass Presque Isle's school farm. As if the beautiful farm were not a sufficient view, this vantage provides sight of another prominence - Quaggy Jo of Aroostook State Park. Compared to Haystack, Quaggy Jo is a young'n.  Formed 410 million years ago, it holds an esteemed place in Maine geology, along with Traveller Mountain and Mount Kineo, as the volcanic remnants of Maine's most intense collision. A microcontinent we call Avalonia was nearing the coast of Maine.  Its leading edge plunged beneath the North American coast. Avalonia would become our coast and the melted ocean would rise up through the ocean to become the aforementioned volcanoes and their granitic roots - some of the largest mountains in Maine.



The collisions weren't over yet. When the last of Avalonia's fore-ocean descended, the sub-continent continued forward. The colliding land masses were too light to sink into the Earth's mantle below, so the smashing crushed everything skyward.  Formerly flat ocean bottom became wrinkled like a discarded sock. In some places in the Appalachians the squished rock climbed higher than today's Himalayas. Here in the county, hundreds of millions of years later, all that's left are the rolling hills that I drove over.

At that turn, on that road, I could see into Maine's geologic past. I saw an ancient ocean lap the shores of Haystack Island. Quaggy Jo volcano erupted right in front of me. The very hill I stood on rippled upward as Avalonia invaded our shore. The chaos of a half a billion years, wrapped into a single panorama on a peaceful hill. 

Boone, Gary, William  Forbes, and Chunzeng  Wang. "Haystack Volcanic Geology and Geologic History." Go Aroostook Outdoors. N.p., n.d. Web. 10 Oct. 2014. <http://goaroostookoutdoors.com/sites/default/files/trails/maps/HaystackGeology.pdf>.



Caldwell, Dabney W.. Roadside geology of Maine. Missoula, Mont.: Mountain Press Pub. Co., 1998. Print.

Roy, David C.. "Geologic Map of the Caribou and Northern Presque Isle 15' Quadrangles, Maine." Maps, Publications and Online Data. Maine Geological Survey, n.d. Web. 10 Oct. 2014. <http://www.maine.gov/dacf/mgs/pubs/online/bedrock/87-2.pdf>.







Skipping Stones at Kettle Cove

An assortment of stones at Kettle Cove,
 including white quartz and gray phyllite 

Chasing my fifteen month old son at Kettle Cove beach means faster glances at the rocks. I absorb the scene but miss a lot of the details.  A lot of flat rocks - good for skipping.  "That's a little too deep bud, let's bring it in." Some nice round hunks of quartz. "It's okay, keep walking and you'll dry off ." More of the same; more flat, more quartz. Not a lot to see, but that says a lot.

Arms of dark rock contain the sands of Kettle Cove beach

Arms of dark rock supply the cove of Kettle Cove. The repeating foliations and large "knots" make it look almost like wood.  A fact that drives the untutored to ask whether it is petrified wood.  It is not.  The physical features have a more involved backstory.  Four hundred twenty million years ago this rock was sediment in a deep ocean.  Sand, silt and clay piled up in a space between continents: to the north what would one day become most of North America to the south Avalon, a microcontinent whose remains form the coast of Maine and parts of Rhode Island, Great Britain and Africa.  It might seem that these layers of rock would become the "tree rings", but the thin sheets would reveal themselves millions of years later.

"Petrified wood" is really ocean bottom rock
split by stretched bands of quartz 

Four hundred million years ago Avalon crept toward  the North American core.  The pressure on these layers escalated. The minerals in mud migrated and aligned themselves to sustain the stress.  The wavy foliations are the result.  The heat and pressure of impact had the added effect of heating quartz to liquid, sending it screaming through cracks and layers.  As things settled down the quartz solidified into extended blocks called dikes.

The collision with Avalon was prelude to the formation of Pangea. As this is now the coast, we know these impacts were not the end of the story. Africa bumped our coast, and then bounced back out to sea (carrying a piece of Avalon with it). Our "petrified wood" does not have stripes of quartz.  It is punctuated by "knots" of it.  As the continents split, the bands of quartz stretched. Some parts spaghettified into ribbons.  Other sections remained thick with tapered edges.  These bulbs, called boudins (French for sausage, which the strands of quartz resemble) become the "knots" in our wood grain.

Inevitably the rock of this formation, having been lain down, rearranged, injected with quartz and stretched, began to break down. Glaciers, rivers and waves have all had their shot at the rocks of the Maine coast, and the most recent of these don't carry rocks very far.  The smallest pieces may end up as mud on the ocean bottom or sand on the beach. The larger chunks stay local. The flattened layers become skipping stones. The round quartz knots roll back and forth in the surf. These remnants remain for my son and me to explore while perusing Kettle Cove.

Bentley, Callan. ""Boudinage" is my favorite geology word - Mountain Beltway - AGU Blogosphere." Mountain Beltway Site Wide Activity RSS. American Geophysical Union, 20 June 2011. Web. 19 Aug. 2014. <http://blogs.agu.org/mountainbeltway/2011/06/20/boudinage-favorite-geoword/>. 

Berry , Henry N. , and Robert G. Marvinney. "The Geology of Two Lights State Park Cape Elizabeth, Maine." Geologic Site of the Month. Maine Geological Survey, n.d. Web. 19 Aug. 2014. <http://www.maine.gov/dacf/mgs/explore/bedrock/sites/jun02.pdf>. 

Tipping the Clown: Changing Density in the Deer Isle Granite

When I was young I had an inflatable clown with weights on the bottom, so you could administer whatever childhood battering you cared to, and the clown would bob back upright.  I recently read about a feature of the Deer Isle Granite that got me thinking about that clown.

Deer Isle Granite: Naskeag Point

The granite that underlies Deer Isle is long.  It extends from Flye Point on the Blue Hill Peninsula to the southern tip of Stonington in the south.  While the rock is all clearly Deer Isle Granite, it is not homogenous.  Going to Naskeag Point on the mainland presents a deep pink, while a visit to Stonington displays a much wanner stone.  The middle ground of Oak point shows something in between.  The source of the redness may lie in oxidized (rusty) iron that replaces aluminum ions typically present in a mineral called feldspar.

Deer Isle Granite: Oak Point

Liquid rock under the surface cools to form solid granite.  As a result of 4.6 billion years of sorting by density, most granite bodies tends to have fairly uniform consistency.  Deer Isle Granite is different.  For some reason, during its formation, two types of magma were mixed together.  Imagine a nice Italian dressing, shaken before being added to salad. The vigorous mixing swirled everything together, but before it could harden there was time to settle.  Less dense materials, high in silicon content drifted to the top, while the more dense, high aluminum content stuff sank to the bottom.  The aluminum portion took on its iron and its rusty hue.

Deer Isle Granite: Stonington

Under normal conditions the weighted bottom of the clown would remain pointed downward.  The Acadian mountain building event was not normal conditions.  A small continent, and the tectonic plate it rode upon, glided across the fluid mantle toward the prehistoric Maine coast and rammed the landmass.  The collision was not a child's smack, but a match full of heavyweight boxer's jabs.  This impact was enough to permanently tip the clown on its side, revealing the changing color.

Dietrich, Richard Vincent, and Brian J. Skinner. Rocks and Rock Minerals. New York: Wiley, 1979. Print.

Hooke, Roger Leb.. "A Geologic History of Deer Isle, Maine." College of the Atlantic, Serpentine Ecology Conference. July 2007. Web. 14 Oct. 2013. <www.coacommunity.net/downloads/serpentine08

Salt of the Earth: The Source of Sodium and Chlorine in Our Oceans

As an adult, I sometimes forget to ask the obvious questions.  Kids, though, they have their heads on straight.  Living near the coast, I have the opportunity to visit the ocean pretty often.  Every once in a while I brave the frigid waters, and inevitably taste the salty sea, but I never really think about where it came from.  

Recently, I chatted with a friend about her grade school classroom.  She shared some of the science questions her students had asked.  "Why is the ocean saltier than a lake, even though it's bigger?"  I gave her the spiel: lakes and rivers have salt, but water moves through most lakes (and all rivers).  Most of that water, including salts, end up in the ocean.  Water has an easy route out of the ocean: evaporation.  Salt has no such egress.  It stays put.  Just like the ocean, some lakes and seas without outflows collect large amounts of salt. Therefore, we have Salt Lake in Utah, or the Dead Sea in Europe.  I imagined the students' next question: "Where did the salt come from in the first place?", and realized I didn't have a clue.

There are clues however.   The first is the quantity of elements in the Earth's crust.  The most common elements in sea salt vary greatly in their places on the list of most common elements in Earth's crust.  Sodium weighs in at number 6, while chlorine doesn't even make the top 20.  Sodium, therefore, is in everything.  Wikipedia lists 139 minerals, that are composed in part of the element.  When granite breaks down in water, a mineral group called feldspar releases its sodium to the water, and the water doesn't let go.  This weathering of feldspar, and other sodium minerals, would have delivered plenty of sodium to the Earth's oceans very early in their history.

Being rarer in the crust, it might seem that chlorine levels wouldn't be nearly as high in the sea.  In the ocean, chlorine content surpasses sodium as dominant element.  Why the strange ratios?  As it turns out chlorine doesn't play well with others.  A chlorine ion, which is a chlorine atom that has stolen another poor atom's electron, is large, at least relative to other common elements on Earth's surface.  The patterns these smaller ions create don't leave room for the hefty chlorine.  Chlorine elopes with a free hydrogen ion, and escapes out a volcanic vent, having never formed a rock mineral.  At the surface the hydrochloric acid splits, with the hydrogen joining oxygen to make water, and the chlorine dissolved in the ocean.  As chlorine atoms throughout geologic history jostled their way to the surface through volcanoes the oceans grew saltier.

Curiosity has always driven my study of geology.  But sometimes I forget the obvious.  The next time I visit the ocean and watch the surf gather on the shore, I'll be thinking of dissolving rock, belching volcanoes and the rivers that  bring their remnant salt downstream, my borrowed childlike wonder having been appeased.

Lorence G., Collins. "Time to Accumulate Chloride Ions in the World’s Oceans." Reports of the National Center for Science Education 26.5 (2006): n. pag. California State University Northridge. Web. 22 May 2014.

"How did the salt get into the oceans at the beginning of their formation?." UCSB Science Line sqtest. University of California, Santa Barbara, n.d. Web. 22 May 2014. <http://scienceline.ucsb.edu/getkey.php?key=2968>.

Groundtruth: Finding Annual Moraines in My Backyard

An annual glacial moraine.

Twenty-one thousand years ago glaciers covered the northern part of the globe.  Their end point in New England can be seen by following the line of Long Island, New York across to Cape Cod and Nantucket.  This relatively straight line is an artifact of the melting edge of the glacier dropping rocks and sediments delivered from the northern part of the globe, year after year.  As the pile of rocks got deeper and deeper it laid the foundation for these scenic places in New England.  Over time the Earth warmed and the glacier receded back to Maine, but it wasn't consistent.  Each winter the glacier moved forward a bit, and each summer it backed off.  Yard by yard and year by year it retreated to its current (not-so) stronghold at the North Pole.

LiDAR image of annual glacial moraines in West Falmouth.The
image above represents about a third of a mile from north to south.

A month or so ago, I ran into a former student who was researching the glacial history of Maine at Bowdoin, and he introduced me to LiDAR (Light Detection And Ranging) hillshade images that are available for large portions of Maine, including my own backyard.  What he revealed was that with the current imaging technology, we could see not only the large scale features, like Cape Cod, but the yearly inchings of the glacier. Unfulfilled with the images on the screen, I went out into the woods to groundtruth the pictures I saw.  Small hills and low areas I have walked over for years without really thinking about their origin were shown to be moraines dropped each summer by the ice sheet as it receded northward.

Looking up a moraine from a lowpoint in the terrain.

Besting Goliath: The Formation of the Pawtuckaway Ring Dike

The Massabesic Gneiss looks like ice cream
swirled with fudge because of heat and
pressure from 500 million years on the surface

It's hard to dodge the mythological when you look at maps of Pawtuckaway State Park.  Some refer to it as the Dragon's Eye, and for good reason; the park features concentric rings of mountains, identifiable as the iris and cornea.  To see it might even conjure up thoughts of a volcanic Mordor, and as it turns out, 150 million years ago, you wouldn't have been all wrong.  Perhaps the best metaphor for the origin of this strange structure is not literary, but biblical.

The Massabesic Gneiss was Goliath.  Forged in the tectonic rift that cleaved coastal New England from its former mooring point in an ancient Africa, it survived a trek across a long vanished ocean and 500 million years of survival at the surface of the Earth.  Its bold endeavors are catalogued in folds left by heat and pressure along the way.

The ice on the trail is a good metaphor for the park.  As the pool
of magma melted the land below, and added weight above.the
land gave way, allowing magma to rise up through the crack.

Massabesic's David, was not a sling, but a hotspot.  A sedentary warm point deep below Earth's surface regularly created blobs of magma that rose upward.  As the continent shifted with the movement of tectonic plates, these blobs left a string of volcanic mountains including Mount Royal in Montreal and Mount Washington farther north in New Hampshire.  Piercing the Massabesic Gneiss would be different.  Per usual the blob rose toward the surface.  Instead of erupting, the magma sat near the surface, weakening the gneiss's structure from below.  A small eruption may have penetrated the enduring rock.  The added weight, like our misplaced feet, was enough to plunge the Massabesic gneiss into the magma below.  David had bested Goliath.

The gabbro that makes up Meloon Hill flowed up through the
cracks left when the roof of the magma chamber collapsed

Over ten million years, this crack in the armor became a passageway for eruptions of magma that had bided their time.  Magma would have oozed up through the cracks that separated the sunken gneiss from that which remained.  An arc of dark colored, large grained rock, called gabbro, confines the southwest part of the Dragon's Eye.  A disk of salt and peppered rock, called diorite, underlies the lowlands.  These darker rocks may have recollapsed and remelted.  This newer, purer magma would have seeped through cracks to form the whitest, hardest rocks in the park: monzonite. 

Millions of years of erosion laid waste to the softer diorite, and shaved quite a bit off of the gabbro.  The monzonite, more resilient than the rest, remained.  Its stark cliffs are now a monument to the epic battle between a seasoned champion and a literal under...dog.  That is, until a new champion arises.

The view from one monzonite ridge to another.
In the middle are the diorite lowlands. 

Dorais, M. J.. "The Massabesic Gneiss Complex, New Hampshire: a study of a portion of the Avalon Terrane." American Journal of Science 301.7 (2001): 657-682. Print. 

Eby, G.N.. "Mount Pawtuckaway Ring Dike Complex." Geology of the coastal lowlands, Boston to Kennebunk, Maine. S.l.: New England Intercollegiate Geologic Conference, 1984. 240-248. Print. 

McGarry, MaryAnn. "Volcanoes in New Hampshire ." Plymouth Portfolio. Plymouth State University, 17 Nov. 2012. Web. 19 Apr. 2014. <http://www.plymouth.edu/eportfolio/view/view.php?id=12819>. 

Reidy, Daniel E.. "Jurassic Period." New Hampshire Geology Home Page. N.p., n.d. Web. 19 Apr. 2014. <http://www.nhgeology.org/>. 

Reunion on Old Orchard Beach

I hadn't taken into account that water has a way of exploiting a weak point.  On geologic maps, a black line with arrows on one side suggests one slab of rock has slid underneath another.  I convinced my wife to drive out to the site of the fault, with the added enticement that it intersected the coast.  A trip to the beach, on a day above 40 in the winter was not to be passed up.  We pulled into Ocean Park, and while my wife fed my son, I scouted the site.  

What I hoped to see was a reunion.  Five hundred million years ago the rock to the south of Ocean Park and the rock to the north found their home on the fringe of a continent called Gondwana. The goliath Gondwana covered an area of Earth a tad bigger than modern Asia centered around the South Pole.  If Gondwana was Asia, then Biddeford and the rock to the south of Ocean Park were part of Japan; Old Orchard, and the rock to the north,the coast of China.  Four hundred ninety million years ago, plate tectonics ripped Gondwana apart.  These hunks of land set sail across the proto-Atlantic, their near hundred million year journey landing them on Maine's coast 400 million years ago.  Unfortunately, tectonics did not set them gently on the coast.  The force of the plates shoved the edge of the Biddeford land mass underneath the one that underlies Old Orchard.  In a moment I could see Gondwana reunited on Maine's shores.

As I climbed the dune to get a view of this collision, I'd already began to lose hope.  The wind blown sand pointed to the fact that no natural bedrock hindered the movement of sediment. Cresting the dune, I saw beautiful beach for miles in either direction, but no fault.  My wife enjoyed the beach, my son gleefully played in the sand and I pursued the only rock bigger than a pebble, only to be chased away by cold waves.  I looked up the beach at Prout's Neck, and down at Biddeford Pool, wistfully considering my chances of convincing my wife to add some miles to our trip.  If I could just see the rocks on either end, I might find evidence of the Gondwanan meeting point.  Why were they so far away?

A wave hit the shore and my mind traveled back that 400 million years.  That wave would have hit the junction of those collided islands.  It would have found the minute space in between that ancient Japan and that forgotten China.  As it rushed in it would have torn away the smallest piece of sediment.  As it poured out, it would have stolen another.  The space in between would have grown larger and larger. Grain by grain it would be filled in with the small fragments that were broken away.  For 400 million years, the trend would continue.  The end point of this scenario had become clear.  

As we walked back down the beach, on the way to our car, I looked at Biddeford Pool and Prout's Neck as stalwart survivors of an intense collision, then a slow bleed.  Each a reminder of a reunion too long ago to have withstood the relentless abrasion of water.

"Avalon Terrane Field Trip." MIT Geology Field Camp. MIT, n.d. Web. 16 Mar. 2014. <http://web.mit.edu/12.114/05_fall/www/nonGIS_data/worlds_end_bos_basin_field_guide_sm.pdf>.

Dorais, Michael J., Robert P. Wintsch, Wendy R. Nelson, and Michael Tubrett. "Insights Into The Acadian Orogeny, New England Appalachians: A Provenance Study Of The Carrabassett And Kittery Formations, Maine." Atlantic Geology 45.0 (2009): 50-71. Print.

"Geology of Massachusetts." Wikipedia. Wikimedia Foundation, 22 Feb. 2014. Web. 16 Mar. 2014. <http://en.wikipedia.org/wiki/Geology_of_Massachusetts>.

Nance, R. Damien. "Late Precambrian–early Paleozoic arc-platform transitions in the Avalon terrane of the Northern Appalachians; Review and implications."Geological Society of America Special Papers 245 (1990): 1-12. Print.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000  

Maine Geology Timeline

I tend to write blog posts in the order I become interested in them.  I may include how long ago events occurred, but when you're dealing with hundreds of millions of years, things get a little abstract. Today I decided to present the information of my blog in timeline form.  Using a web tool at knightlab.com, I created this.  There are some limitations in the software - primarily, the timeline tool does not go back in time to millions of years ago, so I did some messing around with dates to make it work.  Try clicking the arrows on the slides or clicking around the timeline itself to navigate Maine geologic history.  Also, click the links on the slides to find more about each event and how it shows up in the Maine landscape.  Enjoy.

How to Make Bricks in Three Easy Steps

Last weekend my son and I foresook our weekly grocery shopping trip at the West Falmouth Hannaford.  Instead we crossed the bridge on the south end of the parking lot and ended up taking a walk on an ancient sea floor.  Don't get me wrong, this is not a magical bridge that can transport one to a fantasyland.  The bridge was built in 1859 by the railroad company to connect the Hobbs farm to the rest of society.  John Hobbs homesteaded the land in 1775, and before 1859 when the railroad isolated it and the Hobbs sold it, put it to a variety of industrious uses.  Like people of earlier times are fabled to have done, the Hobbs put every part of the land to use.  The trees became oak shingles, the soil was farmed and the clayey sediment was extracted to make bricks.  The story of these bricks extends far beyond the Hobbs enterprising spirit and thousands of years before the clay was first dug.

The story of our bricks began about 22,000 years ago when glaciers covering much of the globe decided to call it a day and begin the slow commute home from Long Island, New York (Long Island formed as the flowing ice of the glacier delivered gigantic piles of rock to its melting endpoint).  At this point, Maine and the rest of northern North America were buried in ice. Heavy, heavy ice.  The normally firm raft of rock, on which our continent sits, sank like a rowboat upon boarding.  As melting glaciers contributed to a growing ocean, this depressed plate would make way for the intrusion of a sea much larger than today's Atlantic.

The land above the sea couldn't wait to cast off its icy water.  Massive streams poured tons of melted ice into the growing sea, but the water didn't come alone. As the rivers raced to the sea their fast current picked up every stone, pebble, sand grain or mote of clay they could carry.  Massive material, like stones and pebbles may have been dropped long before reaching the sea.  When the stream met the water, it rapidly decelerated. Upon slow down, enough sand was dropped to create a river delta as deep with sand as a football field is long.  The sand from this river's mouth can still be spied along I95 between Gray and Lewiston and is currently being quarried in Gray.  But what about the bricks?

The slow moving water, at this point, would have dropped nearly everything.  Robbed of most of its energy by the trudge into the ocean, the sluggish water couldn't carry much.  Luckily, clay is small and light.  The water transported these small grains the farthest, finally dropping them at the sight of the future Hobbs' farm.  About 13,000 years ago, with the weight of ice removed, the plate rebounded, and the sea level dropped.  The acreage of the Hobbs' farm was revealed.  Soil developed.  Oaks grew.  Eventually, the Hobbs would dig up their bricks and my son's and my weight would leave footprints in the ancient seabed.  

McCully, Betsy. "Ice Age." New York Nature. N.p., n.d. Web. 11 Feb. 2014. <http://www.newyorknature.net/IceAge.html>.

Robinson, Michael A., Stewart K Sandberg, and Kirkpatrick Melissa D.,. "Using transient electromagnetic soundings to map the thickness of the Gray Delta, Maine, and correction of data using coil calibration to improve resolution. ." Geological Society of America Abstracts with Programs 33.1 (2000): 1. Print.

Weddle, Thomas K., Gray Quadrangle, Maine, 1:24,000, Augusta, ME: Natural Resources Information and Mapping, Maine Geological Survey, 1997.

"Surficial Geologic History of Maine." Maine Geological Survey. N.p., 6 Oct. 2005. Web. 11 Feb. 2014. <http://www.maine.gov/dacf/mgs/explore/surficial/facts/surficial.htm>.

"River Point Conservation Area." The Town of Falmouth . The Town of Falmouth , n.d. Web. 11 Feb. 2014. <http://www.town.falmouth.me.us/pages/falmouthme_parks/trailmaps/RiverPoint>.

Maine's Pinatubo: Unearthing a Natural Disaster

Soon J.D. Irving Limited may be freed to start thinking about how to take 22 million tons of copper ore out of the ground in northern Maine. The Maine legislature may relax laws regulating the mining of metals in Aroostook County. While Irving consider strategies for extracting copper and zinc, as well as relatively small amounts of gold and silver, I have been thinking about how the metal rich rock, called sulfide ore, got there in the first place. It all occurred about 500 million years ago when a series of islands, not too unlike the Philippine islands, were forming off the coast of North America.

The best lens from which to consider what went into creating the ancient ore might be to consider a more recent event. Twenty-one years previous to the bill being passed, Mount Pinatubo was cooling off after a long summer of letting off steam. In the summer of 1991, the Philippine Sea Plate subducted beneath the Eurasian plate, releasing 10 billion tons of magma in a volcanic eruption. As the magma neared the surface, it released chemicals that refused to join with others to form minerals. Valuable metals, like zinc and copper and dangerous ones like cadmium and lead, were distributed as ash across the Philippine region. Far from a rain of wealth, the ashfall is thought to have significantly shortened human lifespan on nearby islands. Sulfur combined with oxygen in the atmosphere to form sulfur dioxide gas, which in turn joined with moisture in the atmosphere to form sulfuric acid. Aircraft throughout the Northern Hemisphere experienced corrosion damage from the acid for years afterward. It is with good reason that the eruption of Mount Pinatubo was regarded as a natural disaster.

Five hundred million years ago no one was around to experience the ash or acidity of eruptions that formed the islands that would become the metal-rich rock in northern Maine. The islands and the ore formed as two oceanic plates in a proto-Atlantic ocean collided. One plunged beneath, bringing loads of ocean water with it. As the water and the rock descended, both heated. The water would have rushed through subterranean rock, dissolving unmatched elements along the way. The scalding liquid would have picked up sulfur, then metals. It would wend its way upward, cooling as it went. As its temperature dropped the dissolved sulfur, submerged and lacking its partner oxygen, would seek out other mates, finding them in the unmatched metals that flowed alongside. The sulfur/ metal pairs, sulfides, solidified and were stored underground preventing life's exposure to corrosive acids or dangerous metals.

In the next decade J.D. Irving may decide it is worth unearthing the metal-bearing sulfides of Aroostook County. But the price of digging up a natural disaster must be paid. Payment can be rendered in advance if the mining company works to prevent the spread of sulfur and metals into the environment. It can be paid after the fact by the citizens of Maine, in the form of clean up costs. Or, it can be paid by sacrificing the beauty and balance of northern Maine's natural ecosystem. Regardless, the cost must be rendered, and it's best to consider this before the bill comes due.

Beck, Fredrick. "A History of Non-Ferrous Metal Mining and Exploration in Maine." Geological Society of Maine. N.p., n.d. Web. 1 Jan. 2014. <http://www.gsmmaine.org/wp-content/uploads/2010/02/Beck-A-History-of-non-ferrous-metal-mining-and-exploration-in-Maine.pdf>.

Casadevall, Thomas J. , Perla J. Delos Reyes, and David J. Schneider. "The 1991 Pinatubo Eruptions and Their Effects on Aircraft Operations." Fire and Mud: Eruptions and Lahars of Mount Pinatubo. U.S. Geological Society, 10 June 1999. Web. 1 Jan. 2014. <http://pubs.usgs.gov/pinatubo/casa/>.

"Environmental Health and Safety Guidelines Base Metal Smelting and Refining." International Finance Corporation. International Finance Corporation, 30 Apr. 2007. Web. 1 Jan. 2014. <http://www.ifc.org/wps/wcm/connect/4365de0048855b9e8984db6a6515bb18/Final%2B-%2BSmelting%2Band%2BRefining.pdf?MOD=AJPERES&id=1323152449229>.

"Open-pit Metal Mining in Maine." Natural Resource Council of Maine. Natural Resource Council of Maine, n.d. Web. 1 Jan. 2014. <http://www.nrcm.org/issue_mining.asp>. 

"Volcanic Gases and Their Effects." Volcano Hazards Program. U.S. Geological Survey, n.d. Web. 1 Jan. 2014. <http://volcanoes.usgs.gov/hazards/gas>. 

"Volcano or Environmental Disaster?." VolcanoCafe. N.p., 18 Nov. 2013. Web. 1 Jan. 2014. <http://volcanocafe.wordpress.com/2013/11/18/volcano-or-environmental-disaster/>.

The Outcrop in the Crystal

It's my 20th post!  This blog post is the first of several that will highlight an outcrop that drove my interest in Maine geology.  If you're looking for the outcrop it's on Rte. 115 on the Gray/ Windham border.  Or check it out on the Sphere app.  

The outcrop told the story of Maine.  The white rock, a granite, bubbled up when Africa's coast collided with our own 450 million years ago, sealing Maine into the Pangeaic interior.  The black basalt resulted from one of the volcanoes that once again cleaved the supercontinent in two when Pangea split.  The glittery schist told the tale of a muddy ocean bottom that predated both two igneous rocks.  But how did the green rock get there?

There were obvious clues.  The parallel stripes of white, green, and sometimes even gray told tales of piling layers.  The fact that these layers took turns with schist, a mudstone altered by heat and pressure, as one scanned the outcrop from left to right suggested that it, too, formed in that muddy sea.  Other facts didn't add up.  The tough rock scored glass.  Most of the usual sedimentary suspects wouldn't do that; unmetamorphosed mudstone and limestone were just too soft.  Their metamorphic progeny, schist and marble would have crumbled as well.  Sandstone, and its postbear quartzite, would do the job, but the look wasn't right.  The rock lacked the granularity of sandstone, and the sugariness of quartzite.

The truth became clearer as I began to research Silurian time, a period between 416 and 444 million years ago, in which the green rock formed.  The ocean bottom that it gathered in was flanked on three sides.  To the north lie North America, to the south, a hunk of land that would become Maine's coast. To the east, Western Europe plugged another opening preventing the flow of currents.  The phlegmatic basin, just south of the equator, became poor in oxygen, but rich in life.  Lacking our usual breath of life, the creatures of the sea resorted to extreme measures - consuming sulfur.  

The chemistry of this bounded sea played an important role in the green rock's formation.  As a coral reef, in an aerated ocean, degrades, it forms limestone, which is composed of the elements calcium, carbon and oxygen.  Our sluggish sea would have produced a similar product, with one small difference: the sulfur consumption exchanges some of the sediment's calcium for a new element - magnesium.  The rock it forms goes by a different name: dolomite.

Even dolomite doesn't have the strength to scratch glass.  The rock would require one final transformation.  As plates moved, the basin grew smaller, and then disappeared.  The formation of Pangea spurred an influx of fluids: some large, like the bulb of magma that formed the white granite, some less immense, like the infusion of quartz and water that flowed through the ancient ocean bottom.  This liquid sought out any channel it could access, including spaces in the schist, and the dolomite.  The schist proved passable, but inert.  The dolomite was reactive.  The heat and chemicals in the flowing fluid released carbon and oxygen from the dolomite (as carbon dioxide).  Some of the quartz stuck around, providing the white layers of the rock.  The green crystals, a mineral called diopside, kept the calcium and magnesium of the dolomite and replaced the CO2 with silicon and oxygen from the quartz.  

The outcrop is a testament of Maine's geological history.  It documented the marine roots and the accordion push-pull of continents.  The green diopside crystal, a fractal of that outcrop, records the deoxygenated ocean bottom in its calcium and magnesium.  It further tells the tale of the pushing and pulling continents in its silicon and oxygen.  The green crystal, a mere fragment of the outcrop, tells the outcrop's entire story.

Bickle, M. J. , H. J. Chapman, J. M. Ferry, D. Rumble, and A. E. Fallick. "Fluid Flow and Diffusion in the Waterville Limestone, South—Central Maine: Constraints from Strontium, Oxygen and Carbon Isotope Profiles." Journal of Petrology 38.11 (1997): 1489-1512. Print.

Ferry, J. M.. "A Comparative Geochemical Study Of Pelitic Schists And Metamorphosed Carbonate Rocks From South-central Maine, USA." Contributions to Mineralogy and Petrology 80.1 (1982): 59-72. Print.

Fischer, Dan , Tammy (Yue) Liu, Emily Yip, and Korsen Yu. "The Silurian Period."The Silurian Period. University of California Museum of Paleontology, 5 July 2011. Web. 6 Dec. 2013. <http://www.ucmp.berkeley.edu/silurian/silurian.php>.

Hussey, Arthur M., II, 1996, Bedrock geology of the North Windham 7.5' quadrangle, Maine; Maine Geological Survey (Department of Conservation), Open-File Report 96-16, 6 p.

Helmholtz Centre for Ocean Research Kiel (GEOMAR) (2012, June 7). How does dolomite form?. ScienceDaily. Retrieved December 8, 2013, from http://www.sciencedaily.com/releases/2012/06/120607105815.htm

Wilde, Pat , William Berry, and Mary Quinby-Hunt. "Silurian Oceanography."Marine Sciences Group. University of California, Berkeley, n.d. Web. 8 Dec. 2013. <http://www.marscigrp.org/sil91.html>.

Beyond Pangea: The Chain Lakes' Long History

Every middle schooler hears about Pangea.  You look at the world map and envision the ocean closing and that land before time re-forming.  And that's the end.  You don't think about what happened before because no one ever told you that there was a before.  Well, I am here to set you straight.

Don't get me wrong.  Pangea is old.  When Pangea was THE place to be, dinosaurs had not yet set foot on this Earth.  In fact, the dry center of the giant continent set the stage for water loving amphibians to evolve into drought tolerant reptiles.  Later, these reptiles gave birth to the generations that would become the feared lizards we call dinosaurs.  Here in Maine, however, you will find no trace of dinosaurs, because nearly every rock was formed before the oceans that collapsed to make way for Pangea produced their parting waves.

What's important to realize is that the formation of whole Earth continents, like Pangea, is a cycle.  These so-called supercontinents occur occasionally throughout Earth history.    Six hundred million years ago, the supercontinent of the day, one that we call Pannotia, would have filled much of the space taken up by the modern day western Pacific Ocean, and a large hunk of Antarctica, too.  About 1.3 billion years ago, Rodinia was gathering all the Earth's land masses at the equator.  This is the point at which we will begin our journey back to the future.

The Chain Lakes Massif, an elevated hunk of land just north of Sugarloaf, may be the best perch from which to watch the story unfold.  A supercontinent is formed when an ocean closes.  The weighty seafloor rock descends into the Earth beneath the lighter continental shoreline. The diving rock melts, and then reascends, forming a chain of volcanoes, not unlike the modern Andes.  The larger the colliding continents, the larger the mountain chain - and Rodinia was big!  The billion year old mountain chain is now the core of North America, running the 3000 miles from Newfoundland, Canada to Veracruz, Mexico.  Big mountains fall fast, and as rain and ice dragged sediment from the peaks it dropped it into the closing ocean.  Some scientists think it was this sediment that would become the Massif.  As the ocean closed, the sediment may have changed from mud to stone.

A billion years ago Rodinia was formed, but this, too, must pass.  The mega-continent shattered.  While the 3000 mile backbone, called the Grenville Province, stayed intact, the sedimentary shorelines drifted away.  While the cycle continued, the sedimentary island moved along the Earth's surface, but 400 million years after it started its journey, the Massif came home.  As its ocean closed, and Pannotia gathered, the piece of land that would become the Chain Lakes became nestled in the heart of the new supercontinent.  Nestled may be an understatement, because the crushing force of the continent forming squeezed, buried, and roasted the rock, altering it from a simple sedimentary rock to a banded metamorphic one called gneiss.

Pannotia didn't last long, and when the proto-Pangea split, the Massif hung on to what would become North America.  In fact at that time it would have been coastal property, but that would change as oceans closed one more time.  The Iapetus Ocean (Iapetus was the father of Atlas, and the Iapetus was the predecessor of the Atlantic) closed in stages.  The first impact was a set of Carribean-like islands, the next a small continent called Avalon.  Each collision provided more heat and more pressure, driving the gneissic metamorphism of the once sedimentary rock even further; and making the geologic puzzle harder to solve.

The final crunch came as Africa found its place in the Pangeaic landscape.  The world, different than the one in which we now reside, would at least be familiar to our geographic sensibilities.  South America cuddled up with western Africa, and northern Africa spooned by New England.  Pangea may be the first chapter in our middle school geology texts, but it was one of the last in this corner of Maine.

DiPietro, Joseph A. Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Burlington, MA: Elsevier, 2013. Print.

Landing, Ed. "Vestiges of Rodinia: Adirondack and Hudson Highlands." New York State Geological Survey. New York State Museum, n.d. Web. 11 Nov. 2013. <http://www.nysm.nysed.gov/nysgs/nygeology/tectonic/02.html>.

Meert, Joseph . "A History and Preview of Supercontinents through Time." Gondwana Research. N.p., n.d. Web. 11 Nov. 2013. <http://gondwanaresearch.com/hp/supercon.pdf>.

A Piece of Deer Isle: Rapakivi Fingerprints

When I first started learning about rocks I remember being impressed that each rock formation was unique.  The reddish color of a brownstone cobble in Finlayson, Minnesota informed me that the rock had made the 50 mile trip from the iron rich shores of Lake Superior.  I've started to look for fingerprints in rocks, and there is none more common in Maine than the rapakivi crystals of Deer Isle granite.

Deer Isle Stonework in Falmouth, Maine

While the formation has its home on its namesake island downeast, Deer Isle granite is everywhere.  You can hardly take a step in the L.L. Bean flagship store without resting your sole on a slab. I've noted its presence in kitchen counters, cutting boards, and outdoor stonework.  It even secreted itself into the foundation of Yankee Stadium, a long trip for a stone from Red Sox territory.  In any of these locations the rock would be instantly recognizable by its round pink crystals wrapped in a ring of white.

Close up of Deer Isle granite.  Notice the rounded pink crystal
in the center, and the white rim surrounding it.

The ring not only gives up the source location, it tells a story.  The pink mineral, microcline feldspar, is not normally round. When it developed deep under the surface it would have taken the form of a prismatic rod with regular angles. But this was under pressure.  Where the microcline first solidified may have been 10 miles under the surface. That means 10 miles of rock weight are pressing down on our magma stream like the grasp of Superman.  Just like the hero's clutch could turn coal into diamond, the added pressure that comes with this weight turned liquid rock into solid.  But the crystal had formed before its time.

As this slurry of magma and loose crystals rose up toward the surface, the weight pressing on it subsided.  Without the added pressure, the geometric crystals began to melt, leaving only their rounded centers behind. As the ooze ascended, crystal formation conditions changed.  The microcline, more stable in the deeper conditions, would now be replaced by a different mineral, white plagioclase feldspar.  Because the two minerals are very similar, the plagioclase quickly continues the pattern disrupted by the pressure drop.

Conditions must be just so to create this pattern. A cooler magma channel, the white mineral never forms.  The pressure drops too quickly and the pink feldspar melts altogether. Deer Isle granite's unmistakeable fingerprint is a result of its unique story of formation, dissolution, and restoration. This distinctness may be one trait that makes the stone desirable, but it is certainly one that makes it recognizable.

Eklund, O., and A.D. Shebanov. "The origin of rapakivi texture by sub-isothermal decompression." Precambrian Research 95.1-2 (1999): 129-146. Print.

Hooke, Roger Leb.. "A Geologic History of Deer Isle, Maine." College of the Atlantic, Serpentine Ecology Conference. July 2007. Web. 14 Oct. 2013. <www.coacommunity.net/downloads/serpentine08

Nekvasil, Hanna. "Ascent of Felsic Minerals and Formation of Rapakivi." American Mineralogist 76 (1991): 1279-1290. Print.

Prinz, Martin. Rocks and Minerals Simon & Schuster's Guide to Rocks and Minerals.. New York, NY: Simon and Schuster, 1978. Print.

9 Stories from my Stone Pile

1. The Layers

The layers in this rock suggest that it accumulated over time as sediment piled up somewhere. In the case of this rock it most likely occurred at the bottom of an ocean.

2. The Metamorphosis 

The layered rock was exposed to intense heat and pressure. Though not hot enough to melt the rock the heat and pressure were sufficient to cause minerals to migrate through the solid rock toward one another. This migration fused microscopic clay particles into visible shards of mica pictured here.

3. The Mixing

The dark gray rock in the picture above has a composition similar to the rock above. When Africa collided with North America the magma that formed the white rock rose from below the ocean bottom. Hunks of ocean bottom floated in the molten rock like ice cubes as the liquid rock hardened into the light colored rock.

4. The Crystals 

As the light colored magma cooled, similar minerals were drawn toward one another. Because cooling happened deep underground minerals could move freely through the warm liquid. The pockets of quartz (clear), hornblende (black), and feldspar (white) grew larger and larger until they froze into solid crystals.

5. The Big Crystals 

As the mass of crystals from the picture above solidified, they may have shrunk or cracked leaving space for water and more magma to pulse through the spaces. The water allowed the crystals to grow even larger than regular granite, making a rock called pegmatite.

6. The Splitting

As we all know Pangaea was not a permanent fixture. When it split it was not a clean break. Many places in Maine cracked, creating fractures throughout the coastal region. These joints provided space for new rocks, like the black one above to get up close and personal with older rocks.

7. The Black Rock 

Earlier, I mentioned that the light colored magma came when Pangaea formed. Less dense granite tends to form when continents collide, while dark basalt, pictured above is a sign of splitting. As the two hunks of massive continent diverged, magma that formed through this black rock spilled through every crack it could find.  This dark rock is Pangaea's swan song. 

8. The Ice
Bedrock tends to break off at relatively sharp angles.  Streams tend to form rounded rocks.  These stones fall somewhere in the middle.  They have softened edges, but flat faces.  A mile of ice covered this spot several thousand years ago.  The glacier scraped every type of bedrock in Maine, plucking off chunks as it went.  The glacier broke away hard edges, and sanded off flat facets as rocks were dragged across the ground.

9.The Pile 

The glacier grabbed everything it could, from clay to boulders, and everything in between.  Farmers could plough through the small stuff, but these stones got in the way.  As the freeze-thaw cycle of Maine's weather brought stones to the surface, farmers fought back by flinging them to the edges of fields.  Here lie the remains of decades of farm labor and hundreds of millions of years of geologic history.

Unfolding the Camden Hills

Two weeks ago my friend Colin and I climbed Mount Megunticook.  I was bending his ear about a particular rock, or piece of geologic history when he asked me the question: so how did the Camden Hills get here?  The question haunted me.  It's certainly a question I'd pondered.  I just hadn't made any headway.  I'd researched it too; the answers were either non-existent, or just didn't add up. Glaciers? But, ice sheets scoured the whole state.  Why leave peaks here?  Granite? There may be occasional injections of the light colored rock, but no more than other, lower regions of the state.  Over the intervening weeks I revisited both and decided that perhaps the answer lies in the the shattered infrastructure of the region.

I've mentioned in a previous post that this region was ground zero for a major collision between plates, and the impact is still visible on a relief map.  The ridges to the north and west of the Camden Hills look like ripples in a carpet pushed up by slid furniture.  If Africa was a couch, and Maine an area rug, this isn't too far from the truth.  When Pangea formed, Maine's rock needed to take up less space.  Like the carpet, part went up, and the rest stayed down.  The difference is, rock is not so good at bending.  Instead, a wedge of rock cracks off along a fault, and slides up the face of the piece next to it.  This crack-slide scenario occurred twice, with state geologic maps showing thrust faults not far from two ridges: one that includes Levenseller Mountain, Moody Mountain and Philbrick Mountain and another that features Hatchett Mountain and Coggans and Clarry Hills.

If collision shoves rock skyward, extension drops it down.  When Africa moonwalked its way out of Pangea, it stretched Maine behind it.  Certain blocks of Earth dropped down, filling would be holes with wedges of rock.  To the southeast of the Camden Hills, the land quickly plunges to ocean. The state maps once again show a fault and a cross section makes it look as though the fault block  descended with extending crust.

Where does this leave us?  Three hunks of rock stacked up piggy-back and a piece of ocean dropped into a hole left by a departing Africa.  The Camden Hills, with Megunticook the highest mountains on the Atlantic coast south of Acadia, are the top piggy with the drop to the ocean providing stunning views.  Of course, the once neat blocks have been intruded by magma, and worn down by glaciers and time.  But, I believe, these small giants, are more a tribute to the tug of war between continents than the ice and granite.

Bloom, Arthur. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Upper Saddle River, New Jersey: Prentice Hall, 1991. Print.

"Facing Hatchet Mountain." Hope Historical Society. Hope Historical Society, n.d. Web. 15 Sept. 2013. <www.hopehist.com/Himages/HD402.html>.

Flanders . "Mount Megunticook : Climbing, Hiking & Mountaineering : SummitPost."Climbing, Hiking, Mountaineering : SummitPost. SummitPost.org, 12 Oct. 2013. Web. 15 Sept. 2006. <http://www.summitpost.org/mount-megunticook/234387>.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000