Archive | January, 2012

Horizons, Arm of the Sea?

9 Jan

In an earth, or I should say, globe bound way there is one “true” horizon for every point of view, but in our earthy way there are many horizons for every point of view and the “true” horizon is no horizon at all, being a tangent instead, a horizontal plane tangent to the theoretical sphere at an infinitely small point.  On the other hand, the line of rise defined by dusted snow, the line of hill dark through darker trees highlighted by blazing sunset, the fluttering curve where ocean meets sky, these like the expanding and contracting horizons of mind are real and substantial.  Then there are expanding personal horizons.

 

When I go to different places I like to know where I am.  I want to know what to look for in the terrain and what I am seeing.  It takes a while to find the nooks and crannies in the land scape and society of a new place.  Recently moving to the Berkshire hills I sought a key to the local geology and was able to borrow B. K. Emerson’s 1898 classic THE GEOLOGY OF OLD HAMPSHIRE COUNTY.  Emerson’s “horizon”s fit the OED definition, “A plane or level of stratification assumed to have been once horizontal and continuous”.  This definition was pretty clear from Emerson’s usage, unlike many geological terms requiring research before the text could extend the horizons of my knowledge.

 

Geological horizons in these hills were established by glacial abrasion, sea floor sedimentation, and wind and water erosion.  Emerson describes massive folding and crushing evident in rocks around us here where horizons had been solidified through metamorphic processes, then bent, crushed and tilted through tectonic interaction.  That Emerson and his fellow 19th Century geologists could deduce so much of this progression from scattered outcrops, railroad cuts, and mines, is impressive, though missing the timeline and mechanism for these changes.  Mountain building followed by erosion, volcanic intrusion and extrusion,  ocean floor development, followed by mountain building, etc., for more than a billion years, with the cycles lasting 200 million years or more.

 

What about extending my knowledge horizon?  Describing the beds of schist and gneiss  of these hills Professor Emerson writes about decomposition, hydration, and rust observed in rocks from all ages, metamorphic and igneous.  Looking up meanings of geologic descriptive terms and names of various minerals I became aware of water’s central role in many tectonic processes.  I had long thought of the process of creating stone from sand and clay like it was dry pressure and heat that compressed and molded sedimentary layers into rock.  Now it is clear that water with it’s own chemical character, acid or base, salt or fresh, was heated and pressurized with the mineral and organic sediments, was around as well as within magmas, and these powerful solutions extracted available elements for one crystal formation or another.  This was a revelation to me.

 

We think of water turning to steam at 212F (100C) or lower if above sea level, but thousands of feet under ground at temperatures of thousands of degrees whatever scale you use, we can imagine accelerated powerful reactions unthinkable in our temperate climate.  It is fun to think that many of the most interesting reactions involve elements that were accumulated by algae, bacteria, and other minuscule lifeforms, especially metals slowly collected over millions of years, deposited with other sediments, compressed and transformed.  Some of these transformations lead to raw metal veins, others to mineable ores, others to beautiful crystals (gem or cabinet quality in Emerson’s terms), others just “rock” but every rock with it’s own character derived from it’s own history.

 

One question leads to another, and sometimes back to the original question transformed.  Reading this book and looking for answers to the questions it raised began as much as anywhere in the forest and fields here where water springs from the ground in seeps bringing clay out of the ground, the water running off in clay beds within dykes of clay, practically on the surface, or even above, instead of cutting channels in the soil, because the soil is likewise largely clay.  I wondered what is the nature, history and source of this clay.   Professor Emerson never addressed that issue for these hills.  In describing postglacial deposits in the Connecticut River valley, East and below these hills, the clay deposits he discusses are described as Champlain clay.  My research reveals Champlain clay to be a particular clay formed through glacial grinding in a salt water environment.  As glacial fronts pushed South-East across New England (over a 5000 year period) from the Canadian shield, where it was longer lasting and heavier, the  present St. Lawrence Valley was depressed below the lowered sea level and Lake Champlain as well became an arm of the sea under the glacier ice.  Does the clay here remain from post glacial floods 12,000 years ago?  Is it the product of chemical decomposition of these schists and limestones in these post glacial times?  Always more questions and hopefully better ones.

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