64 J. B. Woodworth — Post-Glacial 



Stone for the first time recognized the agency of wind-driven 

 sand in carving rock surfaces. His studies were carried on in 

 the State of Maine, where, he states, " in numerous places, 

 both in Bethel and elsewhere near the mountains, I found 

 bowlders and even small stones which are now being sand- 

 carved by the wind as plainly and incontestably as in Colo- 

 rado." 



The competency of blown- sand to came rock surfaces. — 

 There can be no question that sands driven by the wind have 

 the power to cut away the surface of rocks on which they 

 impinge. The observations of Blake in San Bernardino Pass, 

 of Gilbert in the Great Basin, of Blanford and Oldway in 

 India, and of numerous observers in the desert regions of the 

 Sahara, the Sinai peninsula, and less arid tracts, point conclu- 

 sively to the view that by means of this subtle agency the 

 hardest rocks are reduced to detritus and receive a form pecu- 

 liar to the manner of erosion. 



Prestwich, in his Geology (vol. i, page 145 , says : " On a land 

 freshly emerged from the sea, both rain and wind had necessarily 

 an infinitely greater effect than now, when it is covered with soil 

 and vegetation. Soft and incoherent strata were then subject to 

 rapid wear by surface waters, and loose materials to easy removal 

 by strong winds, as sands now are on the coast, or on bare tracts 

 inland by the like cause. In the same way volcanic ashes, Dia- 

 tomacese, and seeds are transported for hundreds of miles, and so 

 dispersed over wide areas. Sand, when carried by winds over 

 rocks, is known to wear them smooth, and even to line their sur- 

 face with scratches and furrows. In some cases, hard rocks, such 

 as granite, quartz, and limestone, have been polished, and quartz- 

 ite pebbles worn into symmetrical forms by this means. This 

 occurs in countries where certain winds prevail at different times 

 of the year, so that different sides of the pebbles are alternately 

 exposed to the wind-action. In this manner regular pyramidal- 

 shaped pebbles have been fashioned in New Zealand and Egypt." 



This quotation sets forth in brief the class of effects which 

 are sparingly observed in the district to which this paper re- 

 lates. The explanation of the pyramidal-shaped pebbles given 

 by Prestwich differs somewhat from that advanced by Walther, 

 whose account of his observations and the history of opinion 

 in Germany is so good that I venture to quote from his valu- 

 able monograph.* 



Alex. Winchell : Geological Studies, p. 284; 1886. N. H. Winchell : Geology and. 

 Nat. Hist. Survey of Minn , i, p. 541. R. D. Salisbury, Annual Rep't, X. J. Geol. 

 Survey, for 1892, p. 155. 



* Die Denudation in der Wiiste und ihre geologische Bedeutung. Abhand- 

 lungen der math.-physisch. Classe der Komgl. Sach. Gesell. der Wissenschaften. 

 Band, xvi, No. iii, 1891, pp. 445-448. 



The following are some of the foreign papers relating to the formation of 

 carved pebbles : 



