404 T. W. VAUGHAN RESEARCHES ON SEDIMENTATION 



water ; the ratio of wave amplitude to symmetrical ripple-mark ampli- 

 tude; the bathymetric and thermometric ranges of marine organisms. 



This statement regarding modern sediments is not intended to be ex- 

 haustive; its purpose is to indicate what the scope of researches on such 

 deposits should be. The aim of these researches is not only to understand 

 present processes^ it is also to discover and to make available for use 

 criteria to be applied in the interpretation of ancient sediments. 



Ancient Sediments 



Eesearches on ancient sediments should include, besides seeking the 

 general information needed for all sediments, studies of the lateral varia- 

 tions of geologic formations, the causes of cementation, the formation of 

 concretions, the development of secondary stratification planes, replace- 

 ments, vein-fillings, salt domes, etcetera — in fact all diagenetic changes 

 of sedimentary rocks should be studied. The origin of dolomite is an 

 important problem. Among important economic geologic resources that 

 offer fields for further research are deposits or accumulations of coal, oil, 

 gas, phosphate, potash, nitrate of soda, iron ores, manganese, etcetera. 

 Kd attempt should be made to distinguish between researches into prod- 

 ucts of ascertained economic value and researches into products that are 

 not commercially important, because knowledge of both kinds of products 

 is necessary for understanding geologic history. 



From the brief statements that have been made, it is obvious that an 

 adequate knowledge of sediments requires diversity of research in the 

 fields of physical, chemical, physico-chemical, and biologic sciences. 



Inadequacy of some earlier Investigations of Sediments 



Although many valuable researches have been made on sediments, the 

 statement that no sedimentary deposit is adequately understood will 

 probably not be contradicted. The reason of this is that the results of 

 an insufficient number of lines of research have been brought to bear on 

 the problem of the origin of any particular sedimentary formation. The 

 inadequacy of several researches will be briefly considered. 



Certain deposits are practically 100 per cent organic remains, as, for 

 instance, those on the coral reef of Murray Island, Australia. Knowl- 

 edge of the chemical composition of the deposits, of what groups of or- 

 ganisms contributed material to them, and of the proportion contributed 

 by each group of organisms is valuable ; but this information alone is not 

 adequate, for the material has been subjected to sorting by moving water, 



