M. I. Goldman — Catahoula Sandstone of Texas. 277 



Sabban in his paper, cited above, on the dunes of the Meck- 

 lenburg heath, and Retgers in a paper on the dunes of Holland,* 

 both give determinations of the proportions of heavy minerals 

 present ; but as these are for the entire sand or for portions that 

 are not comparable with mine they too are not directly compara- 

 ble. However, the high proportion in Retgers' average for the 

 whole sand (5 per cent) and even the figure for Sabban's entire 

 sand (average estimated over 1 per cent) show that in these 

 dunes the proportion is much higher than in the Sahara sands, 

 while the figures given by Sabban for some of his individual 

 portions suggest a very marked similarity with the Catahoula 

 sandstone. f Theoretical considerations alone suggest the more 

 perfect separation of light and heavy minerals in aeolian sands 

 for the same reason that they are more perfectly sized, i. e. on 

 account of the much lower viscosity and density of air as com- 

 pared with water. However, in the absence of comparative 

 data on this point I do not want to overemphasize it since 

 there is an evident difference between desert and stream 

 deposits, as pointed out by Sherzer and already noted above in 

 the discussion of the percentage of feldspars present, in that 

 the stream of water carries its material continuously in one 

 direction and thus can leave the heavy material behind, while 

 winds do not have this fixed direction and tend more to blow 

 material about in the area in which it originated, so that there 

 is less space for a horizontal separation. Another factor 

 working toward a low percentage of heavy minerals in aeolian 

 sands will be presented under the next heading (Species of 

 heavy minerals, etc.). 



To sum up, it may be said that theory, as well as comparative 

 data about the percentage of heavy minerals present, suggest 

 aeolian action as a factor in the formation of the Catahoula 

 sandstone, while among the aeolian sands with which it can be 

 compared its greatest affinity is with dune sands. 



6. The species of heavy minerals present and their ratios to 



each other. 



Though I have not attempted to determine quantitatively 

 the proportion of individual heavy minerals present, certain 

 facts of their abundance are so pronounced as to permit of easy 

 generalization. Magnetite makes up doubtless over half the 

 sample and zircon most of the rest. It seems as though the 

 predominance of these two minerals is so pronounced that it 

 must have some significance independent of the composition 



* Retgers, J. W. : tlber die mineralogische und chemische Zusammensetz- 

 img der Diinensande Hollands, etc. Neues Jahrb. Min., 1895, i, p. 27. 



f For additional references on the minerals in aeolian sands see Free, loc. 

 cit., p. 68 footnote g. 



