Wednesday, August 10, 2016

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.

Saturday, April 16, 2016

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

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

Saturday, April 11, 2015

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.

Saturday, December 20, 2014

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.

Sunday, October 12, 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. <>.

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. <>.

Tuesday, August 19, 2014

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. <>. 

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. <>. 

Friday, July 18, 2014

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. <