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.

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

A Trip to Baxter Four Hundred Million Years Ago

To visit Baxter State Park during Devonian time would have been quite an experience.  Devonian time extends from 419 million years ago, when fish were just starting to widen their grip as rulers of the ocean, to 359 million years ago, when amphibians were testing their new toes on continental soil.  It is during this period of prehistory when almost the entirety of Baxter's bedrock was lain down.

419 million years ago, to travel the path that one takes to the north entrance of the park from Patten would require a boat.  Paddling north on the route that 159 takes, you'd hit land not far south of Shin Pond and a long portage would take you over the island arc and continue you on your way.  The island extends into the realm of the park only in so much as the rains tearing apart the island, at a snails pace, were delivering the islands sedimentary fragments into the surrounding ocean.  The heavier sand dropped first in a wide delta, while the smaller silt and clay drifted farther into the ocean, only to be dropped when the stream's energy had been almost fully spent.  The sandstone that was once the delta can be found along the eastern edge of the park, while the old ocean bottom wraps the northern and western sides.

The trip up Katahdin would have, in fact, been a descent.  While the portage island was being torn apart, southern Maine was plunging beneath northern. As the ocean bottom sank, it melted.  As it melted it rose, creating an upside down tear drop of magma not far from the surface, but still a ways down from Baxter Peak's current stature.  As the magma cooled, minerals formed creating the small, but visible crystals of the Katahdin granite.  The magmatic elements paired off, leaving behind the ingredients of water vapor.  The bubbling gas rose to the top of the magma chamber.  As the magma hardened around the bubbles it left cavities in which different minerals could form.  The change from the liquid magma chamber which formed the base of Katahdin to the frothy top, which formed the peaks is visible today as the white, even grained granite evolves into reddish, multi-textured granite.

While the Travelers are smaller in stature now, they literally rose out of Katahdin during the Devonian.  The Traveler Rhyolite was the volcano to Katahdin's magma chamber.  A trip there means braving molten lava, but also burning ash.  A hellish expedition to be sure, but at least there wouldn't be any black flies.  The drifting ash interbedded with the lava and then flowed down slope.  In modern times the flow is visible because the gray ash is flattened amidst the white rhyolite.

Later in the Devonian, a trip down the South Branch Pond Brook, geologically, wouldn't have been too much different than it is now.  The towering volcanoes, like the mountains that now stand, would have provided a prime environment for raging rivers powerful enough to break apart and then round the edges of chunks of rhyolite.  Smaller particles would be taken farther off to sea.   This order is preserved in the sequence of rocks below the falls - rhyolite, conglomerate, finer-grained sedimentary rock.

With current technology as a limit, an adventure in Devonian Baxter State Park is of course an impossibility.  The current landscape becomes our only time machine through which to view this exciting period in Maine's history.

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

Rankin, Douglas W., and Dabney W. Caldwell. A Guide to the Geology of Baxter State Park and Katahdin. Augusta, Me.: Maine Geological Survey, Dept. of Conservation, 2010. Print.

"Maine Geologic Map Data." Maine Geologic Map Data. 05 Apr. 2013. Web. 03 July 2013.