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



of extreme weatherings and the same criterion may be used to distinguish 

 volcanic from what ma}^ be termed residno-volcanic sand. The passage 

 of snch volcanic sand into residno-volcanic material has been described 

 by Shaler in his paper previously cited, "Origin and nature of soils" 

 (page 239). In the case of a residual sand subjected to but slight 

 aqneons action of stream or wave, not enough to materially change the 

 form of grannie nor completely remove the coating of iron oxide, we 

 have a subtype of sand which may be termed conveniently aqueo-residual 

 and which may be found to comprise the body of numerous beds of sand- 

 stone and arkose. This explanation is assigned to the formation of the 

 Newark system (Jura-Trias) of the Appalachian region by Eussell, in 

 the bulletin previously referred to (I^o. 52, page 44-46), and its color 

 accounted for. This author believed the red color to have resulted 

 directly from the weathering under warm, moist conditions (pages 27 

 and 30). Barrell has shown that there is reason for thinking that with 

 sufficient time only a moderate heat is required, and that the red color 

 may be developed in subaerial deposits under conditions of aridity.^^ 



Aqueous Sand Types 



For convenience of study, sands which owe their characteristics to the 

 action of moving water may be divided into river and beach sands, but 

 under the microscope they appear essentially alike and are not to be dis- 

 tinguished from one another. In the case of minerals of the same or 

 very similar specific gravity, quite complete assorting may often be noted. 

 The most complete effect of this nature may be obtained, as recently 

 pointed out by Sorby,^* to a bottom current in comparatively shallow 

 water. To use his own language, "more or less perfect similarity in the 

 size of the grains usually indicates a sorting of the material by a current 

 at the very bottom of comparatively shallow water ; whereas great irregu- 

 larity in the size indicates that the material was deposited from much 

 deeper water, in which there was little current at the bottom, though a 

 good deal of current higher up.'^ 



Under such favorable conditions the assorting power of water exceeds 

 that of any of the previously discussed agencies, being approached only 

 by the volcanic and exceeded only by the seolian. Similarity in size pre- 

 supposes that the granules possess approximately the same structure and 



13 Climate and terrestrial deposits. Studies for students. Journal of Geology, vol. 

 xvi, 1908, pp. 285 to 287. 



1* Sorby : On the application of quantitative methods to the study of the structure 

 and history of rocks. Quarterly Journal of the Geological Society of London, vol. Ixiv, 

 1908, p. 185. 



