M. I. Goldman — Catahoula Sandstone of Texas. 275 



mechanically disintegrated glacial material ; chemically decom- 

 posed, water-laid material of a modern temperate humid region ; 

 and water-deposited material originating mainly in a modern 

 arid region. 



But the largest part of Mackie's analyses was made on 

 material from the Old Reel of England,* of which the conditions 

 of origin can only be surmised. Yet in spite of that they are 

 I think very significant, for a glance at his diagram shows at 

 once a striking grouping of the results around two extremes. 

 This general appearance is more significant than actual averages 

 since in the absence of definite knowledge of the conditions of 

 origin of the rocks those whose feldspars fall near the median 

 line must be regarded as inconclusive ; but even the averages 

 support the point, giving 72 per cent for the kaolinized end 

 and. 81 per cent for the fresh. What is of special significance, 

 however, is the fact that extremes are characteristic. Indeed 

 I find it hard to conceive of theoretical reasons to account for 

 the presence of appreciable quantities of feldspars of one 

 condition where feldspars of the other condition prevail. 

 That is, if the conditions are those of mechanical disintegration 

 why should some of the feldspars be decomposed? If the 

 answer is that under such conditions only those along joints 

 or fissures would be decomposed, then at once the extent of 

 Assuring of different rocks under the same external conditions 

 becomes a factor opposing the external conditions. Or the 

 effect of a previous condition of climate still retained in the 

 superficial portion of a rock may, as Mackie himself points out, 

 be preserved in the sediments formed under opposite conditions 

 succeeding. Here too w r e have opposing factors capable of 

 producing any degree of mixture in the product. 



These considerations are presented only to draw attention 

 to suggestions of possible complexities in the problem. For 

 the present the indications that the condition of the feldspars 

 tends to one or the other extreme may be accepted. Hence 

 the intermediate condition of the feldspars in the Catahoula 

 sandstone is after all significant ; for if they were originally at 

 one extreme then that extreme could have been only one of 

 predominant freshness and the weathering, as may so easily 

 have happened, took place after deposition of the material. 

 While I do not mean for a moment to suggest a possible 

 glacial origin for the Catahoula sandstone, it should be noted, 

 since this paper aims to be a purely petrographic study, that 

 there are as yet not known, to me at least, any criteria for distin- 

 guishing the effects of glacial from those of arid conditions in 

 producing disintegration or decomposition of feldspars. 



* Loc. cit., diagram facing page 468. 



