Page:Popular Science Monthly Volume 7.djvu/409

Rh. Let the lines H-H-H, H, represent the limit of the continuation of these beds. In the shaft G these beds also are exposed above those seen in shaft F.

The altitude of the rocks above the line of observation (A, B) is exaggerated about five times. If they were reduced to one-fifth, the proportion between the rocks seen in the various escarpments of these mountains, and those carried away below the broken lines, would be properly represented.



By sinking a shaft, only a little surface along the edge of the strata could be seen; but on the sides of the fold they are exposed for many miles, and often the top or bottom is cleared off for a great space, revealing even the ripple-marks of the ancient sea, or rounded impressions of rain-drops which fell in that elder time; or the sands have buried shells and bones of ancient animals, and they are still encased in the rock; and even impressions of leaves that were buried in the mud can yet be seen in such a fine state of preservation that you can trace their delicate veins.

In speaking of the great upheaval of rocks from which the Uinta Mountains are carved, I have spoken of wrinkling and folding, as if the rocks were always flexed; but these displacements are sometimes attended with fractures, on one side of which the rocks are upheaved, or thrown down on the other. Such displacements are called faults. Faults like these are seen in many places in the Uinta Mountains; one great one, on the north side, the throw of which is nearly 20,000 feet, and many others are found of lesser magnitude.

In speaking of elevation and depression by faulting or folding, it must be understood that reference is made to a change of altitude in