908 



E. M. KINDLE CHARACTERISTICS OP MARINE CLASTICS 



materials were brought into the tank. Instead of the beds of pnre white 

 chalk and clean sand afforded by the saline sedimentation^ the fresh-water 

 tank has given drab-colored chalk bands mixed with clay and a band of 

 muddy sand. The wavy contrast between the base of the upper chalk and 

 tlie clay is due to a slight acceleration of the current and the consequent 

 development of vertical currents on one side of the tank during the intro- 

 duction of the chalk. It has no direct relation to the matters here dis- 

 cussed, but illustrates a peculiar type of structure which may result from 

 semivertical or rotating currents which carry sediment into a body of 



Figure 2. — PJwtograph of a Section formed in fresh Water. 



The same materials in tlie tank introduced in the same order and amount as those 

 used in developing the section shown in figure 1. Note the different order of superposi- 

 tion of the sand and clay in the two figures. 



quiet water. These two experiments show that the tendency of marine 

 sedimentation is toward sharply contrasted beds, while fresh water tends 

 to give beds in which different classes of sediment are not sharply segre- 

 gated, and to furnish comparatively slight contrasts in kinds of strata. 

 The application of this principle in discriminating between marine and 

 continental deposits could be wisely made only by giving due considera- 

 tion to various other factors which might enter into the individual prob 

 lem. In general, however, it would appear safe to infer a marine origin 

 for any series of beds in which pure sandstones and shales or limestones 

 were cliaracteristic aiul sharply defined elements. On the other hand, 



