THE PLEISTOCENE OR GLACIAL PERIOD. 



475 



tions of rock at many points (Fig. 557), and its depositional work 

 by the dunes, which are not rare. The erosive work of the wind is 

 of far greater importance than is commonly appreciated by those 

 unfamiliar with arid regions. Loess apparently of eolian origin, some- 

 times with volcanic dust interstratified, is wide-spread in some parts 

 of eastern Washington and northeastern Oregon. 1 



Fig. 557. — Illustrating wind-carving. Palmetto Mountains, Cal. 

 (Turner, U. S. Geol. Surv.) 



Deposition from solution. — About many springs, as in the Yellow- 

 stone Park, deposits of siliceous sinter and calcareous tufa are now 

 making (Figs. 214-218, Vol. I), and more considerable deposits of the 

 latter material antedate the present by some considerable interval 

 of time. Many of these deposits probably fall within the limits of 

 the Pleistocene period. Their distribution seems to indicate that the 

 sites of deposition have become successively lower and lower, as the 

 valleys have been deepened, the springs taking advantage of suc- 

 cessively lower avenues of escape. Tufaceous deposits of the same 

 type are known at various other points in the western mountains. 



1 Salisbury, Jour, of Geol., Vol. IX, p. 730. 



