348 ANNUAL OF SCIENTIFIC DISCOVERY. 



It is generally believed and stated in the books, that the corrosion of the 

 shells of fresh-water clams, which is observed upon the beak, and which fre- 

 qucntly extends over the whole surface of the shell, as in Unio complanatus, 

 Anodonta implicata, and Lampsilis radiata, for instance, is effected by the 

 dissolving properties of fresh water when impregnated with carbonic acid. 

 It is supposed that the carbonate of lime is converted into the bicarbonate, 

 and in this state dissolved by the Avater. This process may sometimes take 

 place, but it docs not seem to be the commencement of the corrosion. In 

 all the specimens of Anodonta implicata which he had collected at Fresh 

 Pond (about sixty), he found little holes, or channels, from one to three 

 lines in length, piercing the epidermis, and presenting sharp edges, such as 

 would not have been likely to result from a chemical process. Moreover, ho 

 found in many of these holes small worms, and therefore he was inclined to 

 suppose that they commence the process of corrosion in the shell ; that they 

 perforate the epidermis, and after the removal of this, the chemical process 

 above alluded to may take place. How far the same supposition may prove 

 true with regard to sea-shells he was not prepared to say. 



At a subsequent meeting of the Society, during the past year, a communi- 

 cation on the same subject, suggested by the remarks of Dr. "Wcinland, was 

 presented by Dr. James Lewis, of Mohawk, N. J. In this communication 

 Dr. L. says : 



Although I 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 suffi- 

 cient to account for the great diversity of appearances presented by the same 

 species in different localities. 



From what information I have been able to obtain in relation to the geolo- 

 gical characters of various regions in which shells are found, it appears that 

 those bodies of water having large quantities 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 quanti- 

 ties of saline, alkalies, and ferruginous Baits, 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 alkalies. The shells arc very generally eroded. I have 

 also shells from other regions where the saline alkalies are more abundant 

 than lime, and they present the same character. 



I have also shells from Ohio, Illinois, Wisconsin, etc., which arc from 

 streams abounding in lime, and an eroded specimen is seldom to be seen 

 among them, except, perhaps, a few aged shells that arc evidently worn be- 

 long contact with abrading surfaces of other bodies. 



I have also shells from a lake in Herkimcr countv, N. Y., nearly all cf 



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which have perfect beaks, and the few that arc 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 n bed of marl. 

 But more satisfactory proof that the freedom of shells from erosion de- 

 pends on the relative proportions of various salts or alkalies in solution in 



