In the Valley of East Tennessee, Appalachian Mountains, it has been shown by Mr. J. P. Lesley that as much as 35,000 feet of rock have been removed by denudation. But this being from an anticlinal arch, it does not, of course, afford any measure of the extent of the denudation of the surrounding country. Major J. W. Powell, Director of the U.S. Geol. Survey, found that under a similar condition as much as three and a half miles of strata have been removed by denudation from the top of anticlinal beds in the Uinta Mountains.[50] Probably the most enormous displacement of strata which has yet been found is that of the “Wahsatch Fault,” Utah. This fault is about 100 miles in length, crossing the fortieth parallel of latitude from north to south, with a downthrow to the west of not less than 40,000 feet. So clear is the evidence regarding this fault that Mr. Clarence King says “that there can be no doubt of the quantitative correctness of my reading of this tremendous dislocation.”[51] There are other modes than the foregoing by means of which geologists are enabled to measure the thickness of strata which may have been removed in places off the present surface of the country. Into the details of these I need not here enter; but I may give a few examples of the enormous extent to which the country, in some places, has been found to have been lowered by denudation. Dr. A. Geikie has shown[52] that the Pentlands must at one time have been covered with Carboniferous rocks, upwards of a mile in thickness, which have all been removed by denudation. In the Bristol coal-fields, between the river Avon and the Mendips, Sir Andrew C. Ramsay has shown[53] that about 9,000 feet of Carboniferous strata have been removed by denudation from the present surface. Between Bendrick Rock and Garth Hill, South Glamorganshire, a mass of Carboniferous and Old Red Sandstone, of upwards of 9,000 feet, has been removed. At the Vale of Towy, Caermarthenshire, about 6,000 feet of Silurian and 5,000 feet of Old Red Sandstone—in all about 11,000 vertical feet—have been swept away. Between Llandovery and Aberaeron a mass of about 12,000 vertical feet of the Silurian series has been removed by denudation. Between Ebwy and the Forest of Dean, a distance of upwards of 20 miles, a thickness of rock varying from 5,000 to 10,000 feet has been abstracted.