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Human History and Geologic History
Geology imposes on we humans vastly more than most of us acknowledge, or realize. Oh, we realize that some places are good for farming, and others not, and some places have important resources, and other not. And we know that mountains make travel difficult, unless you are in a car on an interstate highway.
An entire book could be written on how the geology of the Mid-Atlantic has influenced the people living here, and occasionally in the geologic history we will run a tangent to mention examples, but let us look at the influence of topography on European migratory patterns in Colonial times.
For people with only their own feet, or horses, or wagons, a rugged mountain is a formidable barrier. A few adventurous individual may explore it, but significant migration and settlement is something else. And even for those adventurers, native American trails were still the best and easiest ways to get to distant places. After all, the local tribes had been living and exploring this land for thousands of years before Europeans got here.
Nonetheless, all Europeans arrived by ship, dumped on the eastern sea board, scattered up and down hundreds of miles of coast, and so any migration had to begin there. But what is more, different nationalities, with different backgrounds, goals and interests tended to come to different parts.
This is simplistic, but immigrants from Great Britain tended to head for New England, and Virginia and south. Those places were dominated by British influence. The Dutch early on populated New York and environs. And large numbers of Germans landed in Philadelphia and quickly headed inland to southeastern Pennsylvania.
At first most inland migration was facilitated by navigatable rivers, but even this is geologically fortuitous. Over the past several thousand years sea level has been rising, and the shoreline inundating the land. These conditions favor the development of barrier islands, and estuaries, and drowned river valleys that make good safe ports. If our ancestors had rather tried to migrate when sea level was dropping rather than rising, and sea level fluctuates up and down all the time, there would have been precious few good ports, and settlement would have been much different. And considering that humans have been around for several million years, a few thousand years difference in human history is not that much. Perhaps part of human expansion and exploration became possible at a certain point in history because geologic conditions favored shoreline development that created good ports.
Nonetheless, in Virginia, most of the eastern seaboard (coastal plain province) was settled by the British and they established farms and plantations in the good soils on the flat topography of the coastal plain. The abundant estuaries made good inland water ways for transportation, and made the shipment of goods in and out relatively easy for the time. You may or many not have noticed, but virtually all the surviving colonial plantation mansions in the coastal plain have their fronts facing the river since the river was the best and most natural "highway" of the times.
But population pressure led to migration inland, but as soon as they crossed out of coastal plain into the piedmont conditions changed dramatically. The basement rocks (felsic igneous and high grade metamorphic for the most part) do not make fertile soils, and there was only poverty for anyone trying to make a fortune there.
And with few exceptions this was true all the way over to the Blue Ridge province, and some parts of the Triassic basins.
Now the Grenville basement rocks of the Blue Ridge province are as bad as the piedmont basement rocks when it comes to soil formation, but scattered there and there are exposures mafic igneous rocks, and these do make excellent soils. The best examples are the Cambrian Catoctin lava flows, and the Triassic intrusives in the rift graben of the Atlantic opening.
And by luck, or deeper knowledge, the people who settled on these lands became wealthy. For example, Jefferson's Monticello, and ?????? Ash Lawn are positioned on such rocks. And you may or may not have noticed driving across the western piedmont and eastern Blue Ridge province (but not Skyline Drive) that most of the time you drive through land that only supports forest, and whatever homes are these from the past (early this century and before) are small and unimpressive. But, occasionally you open out into lush open fields, with healthy stands of crops, and well maintained fences, and dotted along the side of the road huge, beautiful mansions, often these days backed by horse barns and paddocks with well bread thoroughbreds.
And then, almost as quickly you pass out into poor farms that never made it. If you superpose these patterns over a geologic map you would see almost exact correlation with the underlying rocks.
But as the British colonists approached the Blue Ridge mountains they were brought up short. The topography is just too rugged to easily migrate over. The same was not true for the Scotch-Irish settlers. Perhaps it was because the ruggedness of the land with its craggy outcrops reminded them of home, or perhaps it was because they just felt too crowded on the flat lands, or perhaps their long difficult history with the English at home made them leery of living to close to them. One way or another, they found the mountains to their liking and so spread not only up and down the Blue Ridge mountains, but also into the rugged valley and ridge mountains to the far west.
But the Shenandoah valley, and the Great Valley of Maryland and its continuation into Pennsylvania was different. These broad valleys, traversed by long, linear, largely navigatable rivers (at least in high water) and underlain by carbonate rocks that also make excellent soils, were a natural highway, with few significant barriers.
And to the Germans settling in the Lancaster, Pennsylvania area of Pennsylvania these limestone soils almost certainly reminded them of similar soils at home. So as their population expanded they naturally followed these soils southwestward through Maryland and into Virginia, all in the Valley and Ridge province.
The point of this brief history is to point out that human history does not take place in an environmental vacuum. In innumerable ways from large scale migratory patterns, to why two farms next to each other fare so differently, geology dominates and controls how we live and what we can do.
We cannot treat the earth like a black box, remaining ignorant of its demands and constraints. And in many ways our Colonial ancestors understood much more than we do. Oh, of course, they do not have the geological technical knowledge we have, which really did not begin to develop until the 19th century, but they were closer to and more directly dependent on the lay of the land, and its resources, than the average citizen is today. You do see much more walking across the countryside than traveling at 70 mph on the interstate.
But the evidence of geology's influence exists everywhere, even if we do not overtly recognize it. And it can be as simple as wondering why Germanic sire names dominate one place, and English sire names another. Or, why certain architectures show up some places, but not others. After all, Colonial Williamsburg architecture does not show up west of the Blue Ridge.
And coastal plain or piedmont type mansions do not cross the Blue Ridge either. And the one great exception shows the subtlety of what is going on. Belle Grove is located south of Winchester in the Valley and Ridge. It is built in the grand style of English mansions far to the east. Why? Well, in fact, that point is almost directly west of the one place the Blue Ridge mountains are low and not a formidable barrier. And it is on good limestone soils. It was the easiest place for high British culture to penetrate to the west.
The argument here is not that we should know all the ways geology influences us, past and present, but to be aware that it does. And not be surprised when the earth does not allow us to do things we in our hubris and ignorance wish to force it to do.
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