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served great numbers of Unios, of species very fami- 
liar to me, scattered over the cultivated fields, often 
atthedistance of amile 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 
of Rangia cyrenoicles, 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 
