. Elements of geology : a text-book for colleges and for the general reader. Geology. DENUDATION, OR GENERAL EROSION. 275 any extent greater. The accompanying section across Middle Tennes- see shows a vertical erosion of 1,200 to 2,400 feet, over the whole valley of Middle Tennessee, which is sixty miles across and one hun- dred miles long. In most cases the removed matter is not so easily estimated as in those mentioned. The strata in mountain-chains are ^^^?^^ Fig. 251.—Section through Portions of England. usually folded in a very complex way, and then denuded. But the ideal restoration of t
. Elements of geology : a text-book for colleges and for the general reader. Geology. DENUDATION, OR GENERAL EROSION. 275 any extent greater. The accompanying section across Middle Tennes- see shows a vertical erosion of 1,200 to 2,400 feet, over the whole valley of Middle Tennessee, which is sixty miles across and one hun- dred miles long. In most cases the removed matter is not so easily estimated as in those mentioned. The strata in mountain-chains are ^^^?^^ Fig. 251.—Section through Portions of England. usually folded in a very complex way, and then denuded. But the ideal restoration of these may be effected, and the amount of erosion approximately estimated. Figs. 250 and 251 are sections across the mountainous parts of England, as restored by Prof. Eamsay. Average Erosion.—By these methods Prof. Ramsay estimates the denudations over many portions of England to be not less than 10,000 to 11,000 feet in thickness.* Over the whole Appalachian region the denudation has probably been enormous, in some places 8,000 to 20,000 feet. Over the whole region of the high Sierra Eange, as we have shown,f erosion has removed the whole of the Jurassic and Triassic slates, and bitten deep into the underlying granite. The thickness of these slates is not known, but it must be many thousand feet. In the Uintah Mountain region, according to Powell, over an area of 2,000 square miles, an average thickness of three and a half miles has been. Fig. 252.—Uintah Mountains—Upper Part restored, showing Fault : Lower Part showing the Present Condition as produced by Erosion rafter Powell). taken away (Pig. 252), the extreme thickness removed being nearly five miles. From the Wahsatch have been removed 32,000 feet, or * Geological Observer, p. 819. f American Journal of Science and Arts, vol. v, p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may n
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
