M. 1. Goldman — Catahoula Sandstone of Texas. 271 



except that its maximum is in a finer size, and that it contains 

 clay. The reason for the similarities is evident enough — both 

 types are the product of continuous strong wave action. And 

 this leads to a summary statement of the most essential conclu- 

 sion from the diagrams presented. Wind and strong wave 

 action are both capable of producing marked sizing of sands. 

 The Catahoula sandstone, therefore, is the product of one or 

 both of these agencies. To say with assurance that one of the 

 two was alone or predominant does not appear possible. But 

 Mohr's analysis of a weathered beach sand draws attention to 

 a factor which may help in the interpretation. There we see 

 that as the result of weathering the amount of the maximum 

 is decreased and its disintegrated constituents are added to the 

 finer sizes, a process which very probably accounts for the 

 large portion of material next finer than the maximum in 

 the Catahoula sandstone.* Furthermore, the relatively large 

 amount of material in the size next coarser than the maximum 

 makes the Catahoula sandstone resemble more nearly an 

 geolian sand, so that in the decision between beach and seolian 

 conditions the weight of evidence from the sizing of the mate- 

 rial is slightly in favor of the seolian. 



2. Rounding. 



General character. — For the interpretation of the form of 

 grains, as for the topic just considered, the absence of abun- 

 dant quantitative data justifies one in giving some weight to 

 general impressions, and the rounding of these grains is strik- 

 ing, not, that is, so much in the proportion of rounded grains 

 as in the degree of rounding of some of them which, in cases 

 even in the "extra fine" sand, are almost perfect spheres. 

 There are, however, some quantitative data for comparison. 

 The most important of these are for the lower limit of 

 rounding. 



The lower limit of rounding, that is the diameter of the small- 

 est grain that will be rounded under given conditions, is a defi- 

 nite physical factor depending on the specific gravity of the 

 grain (in this case quartz), on its hardness, on the viscosity of 

 the medium (in this case water or air), and possibly on surface 

 tension and adhesion. Observational data on the lowest limit 

 of rounding in aqueous and seolian deposits are scant and incon- 

 clusive. Daubreef has concluded that since grains of quartz 

 less than 0*l nmi will float in water very slightly X agitated no 



* By using Udden's method of determining the proportion of different 

 sizes (by counting under the microscope) and then by counting only the 

 quartz grains, the original sizing of the sand could be determined, but time 

 was lacking for that. 



f Daubree, Geologie Experimental, 1879, p. 256, par. 2. 



\ Italics are mine. 



