Sunday, September 29, 2013

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.

Sunday, September 15, 2013

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. <>.

Flanders . "Mount Megunticook : Climbing, Hiking & Mountaineering : SummitPost."Climbing, Hiking, Mountaineering : SummitPost., 12 Oct. 2013. Web. 15 Sept. 2006. <>.

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