The anticlinal of the Park Range of the Rocky Mountains was cleft down the axis, and the eastern half depressed 10,000 feet. And Mr. J. P. Lesley gives an account of a fault in the Appalachians of not less than 20,000 feet, bringing the upper Devonian strata on the one side opposite to the lowest Cambrian on the other.[[45]]
A fault with a vertical displacement of 20,000 feet was found in the Uinta Mountains.[[46]]
In the Aqui range of mountains, Utah, there is a fault determined by Mr. S. F. Emmons to be at least 10,000 feet.[[47]]
The Grand Cañon of Colorado, in some places 4,000, 5,000, and 6,000 feet in depth, is cut, says Professor A. Winchell, in a plateau which has itself been lowered by erosion to the extent of 10,000 feet; and this plateau occupies an area of 13,000 to 15,000 square miles.[[48]]
The Grand “Wash Fault,” Colorado, has a downthrow to the west of 6,000 feet. The “Hurricane Fault,” close to it, has displaced the strata to the extent of over 12,000 feet.[[49]]
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.