906 E. M. KINDLE CHARACTERISTICS OF MARINE CLASTICS 



sists chiefl}^ in the presence of 2 to 3 per cent of salt in marine waters 

 and its nearly complete absence from continental waters which are not 

 land-locked. 



The outstanding- biological fact connected with the contrast in composi- 

 tion between marine and fi-esh waters is tlie amazing fertility of the sea 

 in life and the relative poverty of fresh waters. 



The fecundity of tlie sea, as illustrated by a mussel bed with "a popu- 

 lation of 16,000 mollusca to every square foot,"^ is nowhere paralleled 

 or approached in fresh waters. The salinity of marine waters results, as 

 is well known, in a complete difference in the kind as well as the quan- 

 tity of life characterizing marine and continental waters. So sharp is 

 the biologic contrast that where fossils are preserved in the rocks no fur- 

 ther criteria, as a rule, are needed to distinguish marine from continental 

 deposits. In both marine and non-marine formations, however, fossils 

 are often absent or so rare as not to be available in interpreting the geo- 

 logical history. Tt is therefore most desirable that we should endeavor 

 to understand and interpret the physical record where the biologieal 

 record fails us. 



The very fact that salt and fresh waters yield such strikingly different 

 forms of life at once suggests the probability of commensurate differences 

 in the physical characters of the rocks formed in fresh and saline waters. 

 Tt may be easily demonstrated experimentally that many kinds of sedi- 

 ment behave very differently in these two kinds of waters. 



Eelative Rates of Deposition in saline and in feesh Water 



The surprisingly different rates at which sedimentation proceeds in 

 fresh and salt water is a fact of importance in seeking for the distinctive 

 features which may be expected to characterize marine rocks. This dif- 

 ference may be easily demonstrated by introducing an aqueous mixture 

 of any fine clay into each of two beakers containing respectively saline 

 and fresh water. The sediment introduced into the salt water will reach 

 the bottom in a few minutes, leaving the water above it clear. In the 

 fresh water much of the sediment will remain in suspension for an in- 

 definite period and the water may be turbid for weeks or months. Ac- 

 cording to Professor Brewer,* even several years may not suffice to com- 

 plete the sedimentation in the case of some kinds of sediments. 



In order to study the differences which mark the processes of sedi- 

 mentation in fresh and saline waters, two sets of experiments were car- 



3 James .Tolinstone : Conditions of Ufe in the sea, 1908, pp. 176-177. 

 ■* VS^illiam H. Brewer : On the subsidence of particles in liquids. Memoirs Nat. Acad. 

 Sci., vol. ii, pp. 163-175, 1884. 



