FOSSIL SHELLS. 



consisting of jointed and striated cylinders with a thin coaly 

 hark. The other and less common species consist of hollow 

 cylindrical stems spreading out from the hase like a root. 



Fig. 88. Fig. 89. Fig. 90. Fig. 91. Fig. 92. 



Limnea longiscata. 



Planorbis evouphalus. 



Melania. 



175. The character of the waters, according as they may have 

 heen fluviatile and lacustrine or marine, from which the several 

 strata forming the crust of the earth were deposited, is betrayed 



Fig. 93. 



Fig. 94. 



Fig. 95. 



Fig. 96. 



by the nature of the organic remains which these strata severally 

 contain. Thus, if we find shells (figs. 88 to 92) analogous in their 

 character to existing fresh-water shells, it may be inferred that 

 the deposits were fluviatile and lacustrine, or at all events that 

 they were fresh-water deposits. 



If, on the other hand, none but marine shells (figs. 93 to 96) be 

 found in any stratum, it may be inferred that such stratum was 

 submerged by the ocean from which the deposits were made. 



127 



