It is plain, from the folding of their constituent sedimentary rocks, that high mountain ranges represent local concentrations of mass, which, in every case, must act as a load imposed upon the earth’s crust in the region of the uplift. This added load may be supported in one of two possible ways. If the crust be strong enough, it may support the load by virtue of rigidity; if it be not strong enough, the range must be supported by flotation of its relatively light superficial rocks in the heavier rocks below. If the rigidity of the crust were adequate to support the load without depression—i.e., if the concentration of mass were limited to upward protrusion—then the added mass of the range would affect measurements of the force of gravity, so that the excess mass could be easily detected and positively proved to exist. The force of gravity . . .