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



igneous rock as the principal source of its minerals, though 

 there is enough microcline to indicate some contribution from 

 metamorphic rocks. Somewhat more trustworthy evidence in 

 the same direction is furnished by the zircons, which are of the 

 igneous as against the metamorphic type.* 



But even if this reconstruction of the source rock were more 

 trustworthy it still would not give assurance that there had 

 been ferromagnesian minerals originally present and eliminated 

 by the conditions under which the sandstone was formed, for 

 if the rock had been, for example, a granite it might yet have 

 been of the alaskitic type and so have contained no appreciable 

 amounts of hornblende or consequently of the ferruginous 

 weathering products epidote and chlorite. Thus the evidence 

 afforded by the heavy minerals for arid conditions is only con- 

 tributory and not by itself conclusive. 



Here more than in any other part of this investigation is 

 brought out the importance of founding the petrographic 

 study of any sedimentary rock on study of its field relations 

 and of the petrography of the rocks, crystalline and sedimen- 

 tary, with which it is associated. The ways in which this 

 might throw light on the particular sedimentary rock under 

 investigation are too many to be enumerated ; but to mention 

 only one point it is evident that if we knew something about 

 the rocks from which the material of the Catahoula sandstone 

 might have been derived it would be possible to reach much 

 more definite conclusions concerning the conditions to which 

 those materials had been subjected in the process of its forma- 

 tion. 



This completes the conclusions drawn from the mechanical 

 and microscopic analysis of the Catahoula sandstone. There 

 remain to be considered the macroscopic characters of the 

 rocks, and of these may be taken up first its open texture. 



7. P aching of the sand. 



On this subject there is but little that can be said. Quan- 

 titative observations have not been made on it because those 

 on modern sands with which it might be compared are for 

 the present so inadequate. Very recently Monsenf has been 

 investigating this question of the relation of pore space to 

 the type of sedimentation. His conclusions, which are not 

 always quite clear, seem to be that deeper-water marine sands 

 are closely packed, as are also those of fresh water ; near shore 

 littoral marine deposits are more loosely packed, while dune 



* Chrustschoff, K. von : Beitrag zur Kenntnis der Zirkone in Gesteinen, 

 Tsch. Min. Petr. Mitth., vii, pp. 423-442, 1886. 



fMonsen, Astrid: Tiber die Packung tertiarer. . . . Sande, etc. (Prelimin- 

 ary paper) Centrblatt Min., etc., 1913, No. 8, pp. 242-245. 



