15 



served great numbers of Unios, of species very fami- 

 liar to me, scattered over the cultivated fields, often 

 at the distance of a mile or more from the Tennessee 

 river, and not nearer to any other stream. It is 

 usually supposed by the country people that they 

 were left in such situations by the Indians, who col- 

 lected them for the luxury afforded by the animal 

 inhabitants; but they appear to be alluvial deposites, 

 the result of ancient inundations, as the land on which 

 they occur has not been overflowed since that por- 

 tion of our country was first cultivated by a civilized 

 people. Similar deposites of fresh water shells are 

 extensively distributed on river lands in Georgia, 

 and they appear to me analogous to those vast beds 

 o^ Rangia cyrenoides, on which the city of Mobile is 

 built, and which exist on all the alluvial coast of the 

 Gulf of Mexico, between Pensacola and Franklin 

 in Louisiana. 



In the southern rivers, great numbers of the 

 Naiades are annually destroyed by the rapid subsi- 

 dence of the waters, which leaves them exposed to an 

 ardent sun. When they have travelled some dis- 

 tance and fail to reach the water, they burrow deep 

 into the moist gravel, and soon perish if the river 

 should not speedily rise. They are also exposed to 

 the attacks of herons and crows, which devour great 

 numbers of them. Hogs, I have been informed, also 



