Page:Popular Science Monthly Volume 69.djvu/428

424 its burden of sharp sand driven along with great force, he obtains some conception of the efficiency of the tool. Quartz sand is harder than any of the common minerals in the rocks. Hurled by the rushing water against the sides and bed of the river, it cuts out a path through the rocks as a file does through soft iron.

Volcanic explosions had nothing to do with the making of the canon. If they had, there would be volcanic rock over all the region instead of in isolated patches, and all the topographic forms would be different. The canon is not the result of cracking apart of the earth's crust. If it were, the rock layers would dip away from the cañon; opposite sides would not match; they would lack marks of cutting parallel to the

bedding; their configuration would be independent of alternating hard and soft layers. The extensive cracking and faulting which does exist has been at right angles to the canon and has presented different kinds of rocks for the river to work upon, thus producing variously shaped walls. As the river carves into succeeding strata the crust is weakened and various buttresses sink towards the river.

Thus all signs lead to the conclusion that fire did not make the canon, nor did wind, nor earthquake, but that it was made by the same agent which in an hour carves tiny channels in a garden after a rain storm. That agent was running water, the water of the Colorado as for unnumbered years it has been flowing from snowy Rocky Mountain ridges to the hot sands which border the Gulf of California.