Shaler.] 
584 
[April 16, 
of less value than those secured from strata of more soluble ma- 
terials. It should also be noticed that the negative evidence con- 
cerning saliferous accumulations is of very little value, for the 
reason that deposits of salt are peculiarly liable to destruction by 
the process of solution. Wherever they are exposed to the surface 
the process of removal is likely to be rapid. It is interesting to 
note that whenever a glacial sheet comes in contact with salt de- 
posits, the erosion of the material must be singularly effective. It 
seems to me not improbable that a portion of the area of certain 
lakes may have been excavated in this manner by glacial ice. Even 
where the masses of saline matter remain buried at considerable 
depths below the surface, the passage of rainwater through the 
materials is apt to lead to their removal. The greater part of the 
known salt deposits yield spring waters which are slowly removing 
the material. In this way a large part of the saline matter which 
has once existed in the strata in the form of rock salt has prob- 
ably gone away to the sea. Owing to its less soluble nature, lime 
and perhaps some of the other precipitates which have gone down 
in desiccation basins may remain to attest the existence of arid 
conditions after the rock salt has disappeared. 
The extent to which the ancient saline deposits have been re- 
moved from the rocks may, in certain instances at least, afford val- 
uable evidence as to the position of the given deposits with reference 
to the sea level since the time of their formation. Although this 
matter is apart from the subject of this paper, I venture to give a 
few instances bearing on the point. In northern Florida and the 
neighboring portions of the southern states, the bored wells indi- 
cate that although the beds for nearly a thousand feet below the 
sea level are of marine origin, they have been drained of the salt 
water originally stored in their interstices. It is difficult to account 
for this removal of the waters of construction from the strata ex- 
cept by the supposition that the region has, since its formation, 
been elevated to a considerable height above the sea. We there- 
fore gain from the evidence in this district an important clew as to 
the former height of the continent in this field. It is, however, 
clear that we cannot, save in particular instances, expect to find 
the saline materials removed from strata which have been formed 
beneath the sea and afterwards elevated above its level, for in the 
Palaeozoic rocks of the Mississippi valley, particularly those in the 
region of the upper Ohio, we observe that the marine waters buried 
in the rocks at the time of their construction, are still retained in 
