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



chemical conditions of weathering ; the scarcity of ferro- 

 magnesian minerals to insolation in an arid region ; and the 

 predominance of the two resistant minerals magnetite and 

 zircon to strong mechanical wear such as, under the circum- 

 stances, is most likely to have resulted from aeolian action. In 

 the seeming porosity of the rock there was some support for 

 the assumption of subaerial deposition. The interpretation of 

 absence of lamination was uncertain, but it seemed likely to be 

 due to rapid deposition such as might be caused by wind or by 

 emptying of a strong current into a quiet body of water. The 

 arrangement of fossils is of two types, one indicating subaerial 

 burial in blown sand, the other also probably burial by wind but 

 in a quiet body of water. It was shown that clay galls in general 

 are produced in regions of loose sand, arid or at least without 

 vegetation, and where there is occasional flooding or washing 

 by rain. Their concentration with the masses of flat leaves is 

 taken to confirm the assumption that the water was quiet and 

 that the burial was by wind-blown material, though it may also 

 indicate that these bodies of water were intermittent or variable 

 in their extension. 



In this paper I trust I have made it clear that I do not, 

 under present conditions of knowledge, consider any one of 

 the lines of evidence discussed as in itself decisive, and that it 

 is only in so far as they combine to point to certain conclusions 

 that any weight is to be ascribed to these conclusions. 



But it must be borne in mind, as brought out by Sorby,* 

 that when obtained in this way most of the evidence derived 

 from the constituents of a sedimentarj^ rock is inconclusive 

 because there is a distinction to be made between the history 

 of the material composing a sedimentary rock and the history 

 of the rock itself. Thus of all the lines of analytic and micro- 

 scopic evidence above the only ones that might not merely 

 survive from an older sedimentary rock are freshness of the 

 feldspars and the ratio of feldspar to quartz. As for the 

 macroscopic characters while they are primary and inherent it 

 should be noted that they throw no light on one of the most 

 fundamental problems, that is whether the Catahoula sand- 

 stone was deposited under an arid climate. For while they 

 indicate wind deposition it is very important not to confuse 

 seolian conditions, that is dune formation, with arid conditions. 

 From scarcity of vegetation in both cases they do have certain 

 characters in common, but dunes can and do exist in the most 

 varied climatic regions, and, therefore, their occurrence throws 

 no light in itself on the important problem of prevalent cli- 

 mate. But these considerations of doubt only help to bring 

 out what is one of the principal conclusions from this paper. 



* Sorby, H. C. : On the structure and origin of non-calc. stratified rocks. 

 Qt. Jr. Geol. Soc, xxxvi, p. 58, 1880. 



