150 



Although T assent to the propositions of Dr. Weinland as being 

 sufficient to explain the subject in some instances, I have not 

 regarded the presence of small worms on shells, nor the presence 

 of carbonic acid in water, as sufficient to account for the great 

 diversity of appearances presented by the same species in diffi^r- 

 ent localities. 



From what information I have been able to obtain in relation 

 to the geological characters of various regions in which shells are 

 found, it appears that those bodies of Avater having large quan- 

 tities of calcareous salts in solution produce shells very little liable 

 to erosion ; while on the contrary, where there is very little lime, 

 and the water holds in solution considerable quantities of saline 

 alkalis and ferruginous salts, the shells are very liable to be 

 eroded. Among the numerous specimens that I have, illustrating 

 the above, are large numbers of shells from streams in Georgia, 

 where the waters abound in saline alkalis. The shells are very 

 generally eroded. I have also shells from other regions where 

 the saliue alkalis are more abundant than lime, and they present 

 the same character. 



I have also shells from Ohio, Illinois, Wisconsin, &c., which 

 are from streams abounding in lime, and an eroded specimen is 

 seldom to be seen among them, except, perhaps, a few aged shells 

 that are evidently worn by long contact with abrading surfaces of 

 other bodies, 



I have also shells from a lake in Herkimer county, N. Y., 

 nearly all of which have perfect beaks, and the few that are eroded 

 are by no means as chalky in their texture as some specimens I 

 have seen from localities deficient in lime. The bottom of the 

 lake, in the instance specified, is a bed of marl. 



But a more satisfactory proof that the freedom of shells from 

 erosion depends on the relative proportions of various salts or 

 alkalis in solution in the water, is presented in a limited body of 

 water under my own immediate inspection. 



Near the village of Mohawk, is a slowly-moving body of water, 

 in which considerable numbers of shells are found. In those por- 

 tions of this body of water where the various salts bear their 

 natural and proper relation to each other, the shells are very 

 perfect, and generally very free from erosions. But at and be- 

 low, where the refuse ashes from an ashery are drained or leached 



