642 W. H. SHERZER RECOGNITION OF TYPES OF SAND GRAINS 



degrees; Eaulin, 28 to 32 degrees, and Hagen, 26.5 to 31.5 degrees. 

 Angles reported as high as 50 to 60 degrees he regards as simply eye 

 estimates. In the case of the lee slopes of the dunes of the Oregon coast 

 Diller reported angles of 40 degrees.^^ In the case of dimes, the angle 

 of the lee slope may he reduced hy rain or other causes. Owing to these 

 high angles of rest and the varying velocity and direction of the winds, 

 steep cross-hedding and irregular stratification are common and charac- 

 teristic.^^ In a recent discussion of this suhject, Barrell gives the fol- 

 lowing needed help to distinguish geolian from aqueous deposits: "The 

 characteristic features of such dune sands, separating them from fluvial 

 or littoral deposits, consist consequently in the homogeneous nature, 

 the development of ^millet seed' texture, and the presence in striking de- 

 gree of cross-hedding which may reach great thicknesses. The cross- 

 hedded strata are abruptly truncated above but flatten out and become 

 tangent to the general stratification at the bottom."^^ 



Eippling may occur in geolian sands, as in those of aqueous origin, but 

 according to Goodchild, in the case of the former the coarser granules 

 occupy the crests of the ripples, whereas in the latter they are found in 

 the troughs. ^^ Coarse gravelly deposits, interbedded with seolian strata 

 and believed to be of torrential origin, have been described by Walther 

 and Goodchild. Owing to the general absence of material capable of 

 forming a cement, an geolian bed would be expected to form a very inco- 

 herent type of sandrock unless the granules were bound together by for- 

 eign material secondarily introduced, such as silica, alumina, calcium or 

 magnesium carbonate, iron oxide, carbonaceous matter, etcetera. Fos- 

 sils would scarcely be expected, but, if present, should be of the land 

 type, and introduced during a more or less stagnant condition of the 

 sand giving rise to the deposit. 



^olian sands may be subjected to the previously described agencies, 

 and new subt3rpes thus originated. Glacio-geolian sand would result from 

 the passage of a glacier over a consolidated ^olian sandstone, detaching 

 and crushing the granules as described for the glacio-aqueous subtype. 

 Residuo-geolian sand would result when such a bed is exposed for a suffi- 

 cient time to the agencies of weathering, the quartz granules being iso- 

 lated by the solution of the cementing material and the decomposable 



^ Seventeenth Annual Report of the TJ. S. Geological Survey, part 1, 1896, p. 450. 



31 See Walther : "Die Denudation in der Wiiste," p. 172. 



S3 Barrell : Relations between climate and terrestrial deposits. Studies for students. 

 Journal of Geology, vol. xvi, 1908, p. 282. 



33 Goodchild : Desert conditions in Britain. Edinburgh Geological Society, vol. vil, 

 1896, p. 212. A very satisfying discussion of rippling and dune formation has been 

 given us by Cornish in the Geographical Journal, vol. \x, 1897, p. 278. See also Cham- 

 berlin and Salisbury : Geology, vol. i chapter ii, p. 20. 



