FUTUKE OP THE SCIENCE OP LITHOGENESIS 743 



tain Tertiary deposits as liuviatile in origin. Penck had previously made 

 suggestions along those same lines from studies carried on during a visii 

 to western America. Since then most of our sedimentsi have been sub- 

 jected to a certain extent to lithogenetic analysis, though we are far from 

 being agreed on all the interpretations which have been offered. 



Microscopic Study of the Sedimentakies 



The microscopic study of our sediments has hardly begun, nor have 

 chemical and physical analyses adequate to the requirements of the prob 

 lem been made of more than a few of our elastics. Neither is the strati - 

 graphic relationship of our chemical deposits better known, while our an - 

 cient reef rocks and otber organic deposits have received hardly more than 

 passing notice, though this does not apply to the coals and other related 

 deposits. Perhaps if we stratigraphers insisted on a more refined classi- 

 fication of our sediments, instead of being satisfied with conglomerates, 

 sandstones, shales, limestones, and some minor types, we would make 

 more rapid progress; for it is my belief tliat ])recision in classification 

 leads to precision in thought, and so is of vast value as a mental dis- 

 cipline. It might not be amis^ to insist that a firm fouiKhiticjji in the 

 classification of our rocks is a needful j^reliminaiT to the building of n 

 permanent superstructure, and to urge that we get together and follow the 

 lead of the pyro-petrographers. 



The Future of the Science of Lithogbnesis 



In the future, the study of lithogenesis must go hand in hand with the 

 study of paleogeography. Neither science can progress without the other, 

 and each is dependent on the other to a degree often too little recognized. 

 For its proper prosecution, the study of the genesis of a given sedimen- 

 tary rock requires not only the chemical, microscopic, lithologic, and 

 paleontological in\'estigation of the mass itself, but its field relations can 

 not be neglected. Moreover, it must be obvious that the history of a de- 

 posit can seldom be fully ascertained from the study of a. limited area, or 

 even of the entire area of its occurrence. The characteristics and distri- 

 butions of the formations representing it elsewhere must be taken more 

 account of in the future than they have been in the past. As an illustra- 

 tion, there may be cited the genesis of the Siluric salts of North America, 

 which can only be understood when the Siluric formations of the greater 

 part of the North American continent are understood. In like manner, 

 the lithogenesis of the Mauch Chunk shale and that of the Pottsville con- 

 LVI — Bull. Geol. Soc. Am., Vol. 28, 1916 



