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Part I Geological Setting One of the most aesthetically appealing aspects of the Highlands is the rocks: big, bold, substantial rocks—from the occasional sheer rock cliff with a skirt of tumbled talus at its base to the stray glacial “erratic” boulder the size of a small house. As we learn in chapter 1, the Highlands are composed of billion-year-old bedrock that formed the roots of the ancient Grenville Mountains. Over the eons, the Highlands rose and fell only to rise again, and the bedrock subsequently folded and transformed under the tremendous pressures of colliding continental plates. The native bedrock metamorphosed into various forms of gneiss, a crystalline rock that is highly resistant to weathering and erosion. The shearing forces of the colliding plates also faulted and fractured the bedrock, creating conduits for mineral-rich fluids that cooled to form veins rich in iron. These deposits of iron served as the impetus for much of the early industrial development of the Highlands, playing a vital role in the rise of the United States as an industrial powerhouse in the nineteenth century. Tens of thousands of years earlier, during what is known as the Wisconsin (or Wisconsinan) glacial episode, a continental-scale ice sheet bulldozed southward across the Highlands, stopping in New Jersey. The resulting terminal moraine forms a boundary separating the northern glaciated and the southern unglaciated Highlands. Chapter 2 recounts how, north of the moraine, glaciers sculpted the landscape, gouging valleys while scraping ridgetops bare. In the glacially gouged low spots, water pooled to form lakes and ponds. The moving ice and meltwater transported, sifted, and deposited sand and gravel in beds tens of feet thick in some Highlands valleys. The resulting valley-fill aquifers serve as a big sponge, holding millions of gallons of potable water (a vital resource, as we learn later in part II, for Highlands residents). Along with geology and topography, a location’s soils are a major determinant of possible human use of the land. Chapter 3 discusses the many factors that determine a location’s soil, attributes of the soil, and how these characteristics vary across the Highlands landscape. On the glacially scoured uplands, the soils are often shallow and rocky; generally unsuitable for agriculture, such areas remain or have returned to forest. In low spots on the landscape, fine-grained clays have been deposited, forming an impervious layer that impedes the downward infiltration of water. Under these conditions, the higher water tables and waterlogged soils promote wetlands vegetation. South of the moraine, the valleys are broader, and the soils, often formed from calcareous limestone, are deeper and mellower, making for rich farmland. The diversity of the Highlands forest and wetland ecosystems that are the subject of part III is a reflection of the interplay between the bedrock geology, topography, glacial history, and soils. 8 Geological Setting ...

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