. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 164 THE PEINCIPLES INVOLVED IN EOCK-WEATHEEINa. begins anew without a moment's intercession, and continues until the entire mass disappears, — becomes itself converted into loose sand drifted by the wind and an agent for destruc- tion. Professor W. P- Blake was the first, I believe, to call pub- lic attention to this phe- nomenon, having observed it while in the Pass of San Bernardino (Cali- fornia) in 1853. G. K. Gilbert has also published some interesting facts as noted by himself while geologist of the Wheeler Expedition w
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 164 THE PEINCIPLES INVOLVED IN EOCK-WEATHEEINa. begins anew without a moment's intercession, and continues until the entire mass disappears, — becomes itself converted into loose sand drifted by the wind and an agent for destruc- tion. Professor W. P- Blake was the first, I believe, to call pub- lic attention to this phe- nomenon, having observed it while in the Pass of San Bernardino (Cali- fornia) in 1853. G. K. Gilbert has also published some interesting facts as noted by himself while geologist of the Wheeler Expedition west of the 100th meridian, in 1878.^ In acting on the hard rocks, the sand cuts so _ _ slowly as at times to pro- '^r^^^'^^'^J-.^^^^^^rft^ cluce only grooved or fan- PiG. 16.—Eock undermined by wind-blown tastically carved surfaces, sand. often with a very high polish. The geologists of the 40th Parallel Survey in 1878 de- scribed like interesting phenomena as observed on the western faces of conglomerate boulders exposed to the sand blast of the desert regions of Nevada. The surface of the otherwise light- colored rock was found to have assumed a dark lead-gray hue and a polish equal to that of glass, while the sand had drilled irregular holes and grooves, often three-fourths of an inch deep and not more than an eighth of an inch in diameter, through pebbles and matrix alike. Professors W. M. Davis,- G. II. Stone,^ and J. B. Wood- ward^ have described pebbles occurring in the glacial deposits ^ It should be noted that the '' sand-blast carving'' described by Gilbert in this report is not due wholly to the action of wind-blown sand. The rock is fine calcareous shale. Through the solvent action of meteoric water the calcareous cement is removed, the fine, argillaceous interstitial material mechanically eroded, while the more resisting granules of quartz sand stand in relief, giving rise to elevated points and ridges. sProc. Boston Soe. of Natural History, Vol. XXVI, 1893, p.
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