418 E. W. SHAAV THE STUDY OF SEDIMENTARY DEPOSITS 



great to harmonize with this inference. At other times we do not know 

 where the material has gone when removed from eroded areas. More 

 often we know of several possible sources for parts of several related 

 clastic deposits. 



In many questions isostasy and gravity anomalies are involved. Can 

 we determine the approximate thickness of light, unconsolidated sedi- 

 mentary deposits through determinations of intensity of gravity? Is the 

 sinking of the great sedimentary basins due to loading alone or in con- 

 siderable part to some other cause? Loading will, no doubt, cause sub- 

 sidence, and subsidence will, no doubt, lead to deposition, but how can 

 either take place without the other as a cause? The process would seem 

 to be self-accelerating, if it could only be started. Does great thickness 

 show orogenic movement near by ? May it not be produced in other ways, 

 as by the filling of a basin, as by shore drift — a basin that is gradually 

 sinking without the accompaniment of mountain-making? 



What are the peculiarities, particularly as to mechanical constitution, 

 of those clastic deposits ordinarily spoken of as chemical and organic, 

 though the material after precipitation has been transported, broken up, 

 and sorted? To what extent were the so-called estuarine deposits laid 

 down in estuaries? 



What are the conditioning causes and mode of development of bedding 

 planes and of joints? What is the exact nature of cementation of sand, 

 and why, except where quartzite develops, does it usually proceed only to 

 a limited extent and then apparently cease ? Why are oil sands less well 

 cemented than other sands? Was the oil present soon enough to check 

 cementation, or did it select uncemented sand because of larger pores, or 

 has it some way of disintegrating sandstones ? What part does capillarity 

 play in the formation of an oil or a gas pool ? 



What are the controlling factors of recrystallization, replacement, the 

 growth of concretions, nodules, and geodes? What are the effects of 

 various pressures in the physical chemistry and geophysics of the sedi- 

 mentary basins ? Why are formations generally so uniform in coarse- 

 ness, and how do coarse materials get far from shore? To what extent 

 must we modify such conclusions as that when a formation becomes finer 

 in grain the direction of increasing fineness coincides with the direction 

 from the old shore or from the source of sediment? 



In conclusion, let it be stated that enough has already been accom- 

 plished through individual initiative to show that valuable economic and 

 other scientific results are to be had through the study of the physical 

 processes involved in the formation of sedimentary deposits, and that 

 organized attack promises to bring about much more rapid progress in 

 the science. 



