286 ANNUAL OF SCIENTIFIC DISCOVEKY. 



ON THE GROOVING AND POLISHING OF HARD ROCKS AND 

 MINERALS BY DRY SAND. BY W. P. BLAKE, U. S. GEOLOGIST. 



The phenomena about to be described were observed in the pass of San 

 Bernardino (California), in 1853. This pass is one of the principal breaks 

 through the southern prolongation of the Sierra Nevada, and connects the 

 Pacific slope with the broad and low interior plain of the Colorado Desert. 

 It is bounded on each side by high mountains ; the peak of San Bernardino 

 rising on the north to the height of about 8,000 feet, and San Gorgonio on the 

 south to about 7,000 feet. The elevation of the summit level is 2,800 feet 

 above the Pacific, and the width of the gap at that point is about two miles. 

 On the eastern declivity of the pass the side turned toward the desert the 

 granite and associated rocks which form the sharp peak of San G-orgonio, ex- 

 tend down to the valley of the pass in a succession of sharp ridges, which 

 being devoid of soil and vegetation, stand out in bold and rugged outlines 

 against the clear unclouded sky of the desert region. It was on these pro- 

 jecting 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. For a 

 moment it was impossible to realize the cause of all this abrasion performed 

 in a manner so peculiar. The action of glaciers and of drift was thought of in 

 succession, but the appearance of the surface was so entirely different from 

 that of rocks which have been acted on by these agents, that I could not 

 regard them as the cause. "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. When I stooped down 

 and glanced over the surface of the rocks, I saw they were enveloped in an 

 atmosphere of moving sand, which was passing over and accumulating in deep 

 banks and drifts on the lee side of this point. Grains of sand were thus pour- 

 ing over the rocks in countless myriads, under the influence of the powerful 

 current of air which seems to sweep constantly through the pass from the 

 ocean to the interior. "Wherever I turned my eyes on the horizontal tables 

 of rock, or on the vertical faces turned to the wind the effects of the sand 

 were visible ; there was not a point untouched, the grains had engraved their 

 track on every stone. Even quartz was cut away and polished ; garnets and 

 tourmalines were also cut and left with polished surfaces. Masses of limestone 

 looked as if they had been partially dissolved, and resembled specimens of 

 rock salt that had been allowed to deliquesce in moist air. These minerals 

 were unequally abraded, and in the order of their hardness ; the wear upon 

 the feldspar of the granite being the most rapid, and the garnets being affected 

 the least. Whenever a garnet or 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. A portion, however, of the feldspar upon the lee 

 side of the garnets, being protected from the action of the sand by the superior 



