The existence of mountain ranges in western America formed by the tilting or relative uplifting of great blocks of the earth’s crust, acting as comparatively rigid masses, with subordinate or no flexing or folding of the strata, was first pointed out by G. K. Gilbert in 1873.* He presented and discussed a number of sections and descriptions of ranges in Utah and eastern Nevada, showing the futility of any folding and denudation hypothesis, and the applicability of the notion of origin by faulting. As the ranges of the Great basin form a rather distinct geographical system, and as the faulted block structure was supposed to be the prevailing type, Gilbert discussed it as the structure of the Basin Range system. Not long afterward, Powell, † in outlining the different types of mountain origin, described the formation of mountains by the tilting of faulted blocks as the “Basin Range type.” . . .