514 SHAW: SEDIMENTATION 



its transportation; and the processes which modify strata and 

 their component materials after they are laid down. The term 

 sedimentation should cover these related matters, else another 

 term is needed, for it seems impracticable to isolate these three 

 branches of investigation. 



The interpretation of a layer of sediment may involve the 

 examination of the parent rocks or organisms or solutions from 

 which it was derived and a study of the transporting agents that 

 brought it to its present position. It may be possible occasion- 

 ally to trace ancestry back through several generations of strata . 

 but the numbers of individuals in each preceding generation 

 usually show an increase more rapid than the usual biologic 

 ratio of 2, and one is soon lost in a maze which generally ob- 

 structs attempts to trace Uneage back to the ancestral igneous 

 and metamorphic rocks. 



It is rather curious that although the problems of sedimenta- 

 tion are relatively simple, advances in the science, in the opinion 

 of some, have been of a slow and halting nature. The tempera- 

 tures and pressures involved in processes of sedimentation are 

 of a low order compared with those concerned in the study of 

 igneous rocks. One or more of the processes are everywhere in 

 operation; many of them can be reproduced in large part, some 

 with simple apparatus; and the deposits themselves are fully 

 exposed to view and ready for inspection and sampling. 



Apparently there have been and will continue to be two gen- 

 eral ways of making progress in knowledge of sediments: One 

 is through contributions from geologists in general and paleon- 

 tologists in particular, who gather facts and formulate ideas in the 

 course of their other work. For example, A. C. Veatch observed 

 impressions of upright trees and, with the associated stratifica- 

 tion, interpreted a formation as made up of sand dunes. Ste- 

 phenson suggests that pebbles worn to disc or oval shapes indi- 

 cate wave action on a beach. Ulrich has outUned the general 

 conditions of deposition of various formations. The other 

 method is by special deductive or inductive field, laboratory or 

 closet studies of selected sediment problems. Up to date there 

 have been many contributions to the first class; to the second, 

 few. 



