CHEMICAL SCIENCE. 349 



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 sh'ells are found. In those portions of this body of 

 water where the various salts bear their natural and proper relation to each 

 other, the shells arc very perfect and generally free from erosions. But at, 

 and below, where the refu.sc ashes from an ash cry arc drained or leached into 

 this body of water after every shower, a considerable quantity of saline alkali 

 finds its way into the water, where, in consequence of its specific gravity, 

 it falls to the bottom, and every shell within reach of the influence of this 



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alkaline matter, is more or less eroded, and most of them very much so. 

 But further down, the shells grow more perfect, probably in consequence of 

 the dilution of the alkalies, and their more general diffusion in the whole body 

 of the water, by the influence of the slight current in it. 



It may be thought strange that the presence of saline alkalies in water is 

 urged as the cause of the erosion of shells, but it may be explained in this 

 way. Where two or more alkalies are present in the food of an animal, and 

 only one of them is accessary and proper to enable it to perform its healthy 

 functions, the others may, in part, take the place of the proper substance, and 

 if so, the shell formed under such circumstances would be more or less liable 

 to erosion, in proportion to the solubility of the substituted materials. 



"NVc have now only to inquire respecting a locality producing eroded shells, 

 Is the water so highly charged with lime, that the presence of a more 

 soluble alkali in small quantity can have no material influence in the forma- 

 tion of the shells ? If the answer be yes, then we may reasonably ascribe 



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the eroded character of the shells of such a locality entirely to minute para- 

 sites ; but if there be a preponderance of saline alkalies in the water, they 

 may be reasonably expected to enter into the organization of the shells, and 

 -a very slight abrasion of the epidermis of the shell from any cause, would 

 expose the soluble alkalies to the solvent action of water alone, and the 

 remaining portion of the shell becoming less dense (and "chalky") by a 

 removal of a portion of its substance, would, of course, wear away very 

 rapidly. It is easy to understand why the beaks of bivalves, and the apices 

 of univalves are first attacked by the erosive process. Firstly, the epidermis 

 is thinner at those points : secondly, those portions of the shell formed in early 

 life may be presumed to contain more gelatinous, and less calcarious, matter 

 than the parts formed at or near maturity. I do not know demonstratively 

 that this is the case, but analogy teaches it. 



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