DEFLATION IN DRY VALLEY 61 



the rock flour down the slopes, but it is to be remembered that when the 

 mud has dried out, wind is free to undo much of the work accomplished 

 by water. Our observations did not suggest the presence of a larg( 

 amount of detritus in process of slow transportation by wash. 



The character and size of the residual blocks, the vertical distance 

 through which the Dakota fragments have descended — about 1,000 feet — 

 the scattering of debris so evenly alike over valley floor and intervening 

 ridges, seem to me to harmonize with the view that wind has been the 

 dominant agency in the removal of the sediments below the Dakota level, 

 and may be throughout the work in the same degree that its power is 

 evidently far more efiicacious than that of water at the present time. 



That water has played an important part in the topographic history in 

 producing an initial drainage system of canyons penetrating below the 

 Dakota level is perhaps suggested by the sharp canyons at the head of 

 Dry valley, "Canon Pintado" of Newberry, Cold Spring canyon, and two 

 others, unnamed, which are shown on the Hay den map. Whether or not 

 one postulates a system of such canyons originating under more humid 

 climatic conditions than those of today, wind action alone would seem 

 competent to remove the rock waste of the ridges between gorges and at 

 the same time leave behind the blocks which have been described. 



I was not familiar with the details of Walther's^^ elaborate discussions 

 of denudation in desert areas when the visit to Dry valley was made. 

 The facts observed forced me to the independent conclusion above pre- 

 sented; but the student of Walther's treatise will see much in what has 

 been narrated confirming the views of the German geologist as to the 

 great part played by the wind in the erosion of desert provinces. Especial 

 interest attaches to such confirmation in this case, since Walther has ex- 

 pressed the belief that deflation has been a very important process in the 

 sculpturing of many vast amphitheaters of the Grand canyon above the 

 Esplanade." His view was based iipon general considerations and per- 

 sonal impressions and lacks the support of detailed facts of observation. 



Application to Plateau Province 



The observations here recorded were made during a hurried journey, 

 when attention was particularly directed to problems quite different from 

 those of denudation. Important evidence bearing on the siibject of this 

 paper may have been overlooked, and hence too broad generalization must 

 be avoided ; but it is well known that the Vermilion Cliff and White Cliff 



" J. Walther : Das Gesetz der Wiistenbildunsr. 



" Johannes Walther : Die nordamerikanischen Wiisten. Verhandl. Gessellschaft fUr 

 Erdkunde zu Berlin, band xix, 1892, p. 52. 



VII — Bull. Geol. Soc. Am., Vol. 10, 1007 



