M. 1. Goldman — Catahoula Sandstone of Texas. 273 



found in known wind-borne material justifies the conclusion 

 that at least part of the material of the Catahoula sandstone 

 had been blown about by the wind. 



Proportion of rounded grains present. — For the interpreta- 

 tion of what may be called the amount of rounding of the 

 sand, Mackie* has established a method and given some results 

 which may be used for comparison. The method, essentially, 

 consists in determining the proportion of rounded to angular 

 grains. The results for quartz grains are :f 



River sand of Spey Mostly angular 



c -, T • ., i Round 33 per cent 



Sea sand, Lossiemouth ■< A , _J , 



( Angular 67 per cent 



r\ it-- rj i ^i ( Round 18 per cent 



Culbin dune sands 1 a i ■ n«T 



L J ( Angular 22 per cent 



^ , , , -. , ( Round 29 per cent 



Catahoula sandstone ■< A \ h-t *. 



I Angular 1\ per cent 



In the proportion of rounded quartz grains present, then, the 

 Catahoula sandstone is much more like Mackie's sea sand than 

 like his seolian sand. 



3. Ratio of Feldspar to Quartz. 



Efforts have been made to find some connection between the 

 relative number of quartz and feldspar grains and the condi- 

 tions of origin of sediments. It has been shown by MackieJ 

 that soft minerals (that is above all feldspar as compared with 

 quartz) tend to be eliminated by abrasion in water transporta- 

 tion. He gives for the average of the sands of four rivers 

 near the sea 18 per cent feldspar, and for beach sand only 10 

 per cent. On the other hand, since wind is a less viscous 

 transporting agent than water, this same process should be still 

 more rapid in wind transportation ; and, in dune sands that 

 have been blown about a long time this is so.§ But as Sherzer 

 notes, this state is not generally reached in desert sand because 

 unlike water-deposited sand it remains in the region in which 

 it forms, and, therefore, constantly receives fresh additions of 

 fragments from the decomposing country rocks. 



While I have determined the ratio of feldspar to quartz only 

 in the "very fine" light portion, it maybe assumed that the 

 ratio in other portions would not be very different. This 



*Mackie, Wm.: Hounding of particles of sand, cited above. 



f In order to make his figures comparable with mine I have converted his 

 factor into percentage values, distributing his subangular grains equally 

 between rounded and angular. 



X Mackie, Wm. : The sands and sandstones of E. Moray, Trans. Geol. Soc. 

 Edinburgh, vii, p. 149, 1896. 



§ Sherzer, loc. cit., p. 640-1. 



