Now that the leaves and most flowers are gone for the winter, we suddenly begin to notice all the rocks cropping up around Rye. And for me, rocks bring to mind ancient, prehistoric times.
By Bill Lawyer
Now that the leaves and most flowers are gone for the winter, we suddenly begin to notice all the rocks cropping up around Rye. And for me, rocks bring to mind ancient, prehistoric times.
The earliest prehistoric human settlers of the area now known as Rye, New York, arrived after the last ice age, some 8,000 years ago.
We now know this to be true, but back when the first European setters arrived, most people believed that the entire world wasn’t created until about 6,000 years ago.
Even when I was in college in the 1960s, the idea that the earth’s crust has been floating around in the process known as plate tectonics wasn’t considered to be an indisputable “fact.”
The idea that the earth’s rocks and fossils tell us that the earth was billions of years old wasn’t really considered until some 300 years ago. When people discovered marine creature fossils high up in the Jura Mountains of Europe, for example, they reasoned that these were put there by God’s hand for humans to enjoy.
One early hint that our rocks were much older than the Bible suggests was the study of the formation of stalactites and stalagmites in limestone caves – geological history being made before our very eyes. And then of course there were the volcanoes. And Stonehenge. And dinosaur skeletons. And tar pits.
Geology and evolutionary biology were developing hand in hand during the 19th century.
Nevertheless, while scientists scoured the hills and valleys of Europe and North America for geological clues, most people just made the most of what they found in the ground around them beneath their feet. Or in the outcroppings that were staring them in the face.
Practical human beings from the Stone Age on up figured how to put rocks and minerals to use. They developed highly refined stone masonry skills, and they figured out how to convert clay into all sorts of practical materials.
While they may not have understood the forces that created the different types of rocks, they were able to describe the three obvious types of rocks – igneous, metamorphic, and sedimentary. Each type has particular characteristics that make it suitable or unsuitable for common human uses.
With all the construction and lawn care going on around Rye, you don’t have to look very hard or far to see many examples. Most of Westchester’s bedrock is either metamorphic or sedimentary. Along the western side of the county it’s mostly Gneiss, while on Rye’s side, it’s Schist – both metamorphic.
And, both are very widely used in local building projects – either adding it to level lots and build retaining walls, or removing it through rock chipping to create subterranean basement space.
They’re also used for road building. Back in the 19th century most of the early dirt roads were converted to gravel through the use of metamorphic rock quarried locally where the rock was easily removed from outcroppings.
Westchester also has sedimentary rock – such as limestone or shale. These were also used for construction, but frequently converted to other forms, such as lime or bricks. Shale is formed when clay is compacted by pressure. Both limestone and shale have been highly important sources of information for scientific efforts to understand the earth’s geological history. That’s where the fossils can be found. Limestone was formed when Rye’s area was under water.
Without getting into a complex scientific discussion, geologists say that the current situation has been caused by two major collisions: one between what is now North America and Europe, and the other between North America, Europe, and South America. At one point the land that is now Rye was at the equator!
Currently America and Europe are moving apart – about two inches per year. (No wonder airfares are going up.)
As the plates moved around and “crashed” into one another, mountain chains rose up and then eroded away. Through folding and faulting, rocks that were once horizontal were broken apart and turned vertical.
Westchester County’s river valleys – Blind Brook, Hutchinson, Bronx, and Saw Mill – clearly show how the folding worked as these crashes occurred.
You can also easily see this phenomenon by walking or biking around Rye. Check out the rocks at the Rye Nature Center, Rye Town Park, Playland, or near the corner of Playland Parkway and Midland Avenue. You can see rocks that look like slices of layer cakes turned sideways.
Sedimentary rock from the erosion of ancient mountains turned into metamorphic rock due to extreme pressure from above and heat from the center of the earth.
While many people may find geology boring, because changes normally occur so slowly, that’s certainly not the case for people living in earthquake- or volcano-prone areas.
And, recently, with all the controversy regarding “fracking” to get natural gas from deep below the Marcellus shale, we all need to make ourselves more familiar with what’s going on geologically – right under our backyards.
