Page:Popular Science Monthly Volume 8.djvu/314

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THE POPULAR SCIENCE MONTHLY.

THE SAND-BLAST.
By W. S. WARD.

PROF. WILLIAM P. BLAKE, in a communication "On the Grooving and Polishing of Hard Rocks and Minerals by Dry-Sand," which appeared in the American Journal of Science and Arts, September, 1855, describes the phenomena observed by him in 1838, in the Pass of San Bernardino, California, as follows: "On the eastern declivities of the pass, the side turned toward the desert, the granite and associate rocks which form the sharp peak San Gorgonio extend down the valley of the pass in a succession of sharp ridges, which, being devoid of soil and of vegetation, stand out in bold and rugged outlines against the clear, unclouded sky of that desert-region. It was on these projecting spurs of San Gorgonio that the phenomena of grooving were seen; the whole surface of the granite over broad spaces was cut into long and perfectly parallel grooves and little furrows, and every portion of it was beautifully smoothed, and, though very uneven, had a fine polish." While contemplating these curious effects, the solution of the problem was presented. The wind was blowing very hard, and carried with it numerous little grains of sand. A closer examination disclosed the fact that the whole of the polished surface was enveloped in an atmosphere of moving sand, and it was through the grinding and rubbing of these minute but numberless quartz-atoms that the rough surfaces of these rocks had been made smooth, and the natural grooves deepened and polished. "Even quartz," he observed, "was cut away and polished; garnets and tourmaline were also cut and left with polished surfaces. . . . Whenever a garnet or a lump of quartz was imbedded in compact feldspar and favorably presented to the action of the sand, the feldspar was cut away around the hard mineral, which was thus left standing in relief above the general surface."

The traveler whose good fortune it is to visit our Western wonderland, will note among the many fingers in his guide-book one pointing in the direction of the now famous Monument Park. Entering a narrow valley bordered by mountain-walls, he will find himself gazing in wonderment at the rounded stone columns, rising about him in groups or singly, to a height ranging from ten to forty feet, and in many instances surmounted with grotesque cap-like coverings, that rest balanced upon the frail pinnacles of the rock-columns. An inquiry as to the causes of their existence, standing as they do in isolation on the surface of the valley lowlands, will elicit the reply that they were made by the wearing away of the surrounding rocks by sand, which, whirling about in water or air eddies, acted like chisels of the turner's lathe. Where the depressions were deepest there the