SHAw: sedime;ntation 515 



Notwithstanding the fact that advances have been made, there 

 is as yet no adequate systematic classification that is generally 

 acceptable. There is not even a satisfactory nomenclature. 



There are many features of sedimentary deposits that are not 

 understood and are passed unexplained. Concretions, clay balls, 

 mud pebbles, quicksand, singing sand and a large number of 

 less common nameless features are famihar but not thoroughly 

 understood. There are also, for example, extremely interesting 

 problems concerning the development of beaches, the conditions 

 that control the amount of wave erosion which a subsiding land 

 undergoes, and so on. One may assume that wave erosion is 

 most vigorous at the seaward end of a peninsula that is bordered 

 by deep water. Yet the offshore slopes both at the south end 

 of the Florida peninsula and off the mouths of the Mississippi 

 are above average, whereas wave erosion is below the average. 

 At the mouths of the Mississippi the average offshore slope is 

 about 60 feet to the mile, yet houses built on piles whose tops 

 are 4 to 6 feet above sea level are reasonably safe even in a West 

 Indian hurricane. 



Progress in deciphering the processes of sedimentation is 

 difficult ; the quantity of data and number of working hypotheses 

 to be borne in mind are legion. Lack of progress has been due 

 not only to neglect and oversight but to inherent difficulties. 

 A review of a piece of work in sedimentation is likely to call 

 forth the remark, "Fundamental problems are still unsolved." 

 Too much must not be expected from little expenditure of energy. 

 It is equally true that coordination of effort is necessary for the 

 best results. 



We must admit that we can see only dimly the conditions under 

 which many of our most familiar formations were laid down. 

 We cannot yet write the equation for the reaction which in Na- 

 ture's laboratory produced the St. Peter sandstone. We can, 

 of course, write: a supply of sufficiently coarse-grained material 

 exposed at the surface -f suitable agents operating in the right 

 direction for its transportation + land of suitable surface con- 

 figuration and altitude + disposal by some means of aU other 

 freight carried by these agents -|- wind or some other work to 



