50 Miscellaneous Geological Topics 
mould ; beneath that we find a stratum of deep red clay, very hard 
and tenaceous, of about four feet in depth, and abounding in alumina, 
iron and lime. The next, or substratum is that which extends to 
the sand ; it is of a pale yellow color, contains-less alumina and a_ 
very little iron, and abounds in comminuted.arenaceous quartz. By 
attrition in water it has been rendered as fine as the sand of Arabia, 
which is now extending the limits of Cobi, in Asia, and similar causes 
are enlarging the desert of Sahara, in Africa; where floods of sand 
. are carried upon the wings of the wind, until-countries and cities are 
overwhelmed and lost beneath its accumulating mountains. — - 
Jn this stratum, the snail shells are regularly distributed throughout 
this-region, and are found in every foot untill you reach the sand. 
Upon examination of the bluffs made by the inroads of the Missis-- 
sippi, we uniformly find the shells thus deposited. Now as these 
snails must have been buried by the gentle alluvion of the higher 
land and as the present bluffs formerly receded by a gentle declivity 
for ten miles into the rear, until they ended in a plain,—where would 
they find a limit? Is it not evident that they did once extend by a 
gradual depression, until they were lost or gently died away? ‘There 
is but one species of snail found buried here, and they exist at this 
time very extensively ; and can be found under the bark and in the 
cavities of rotten wood. ‘There is another species of snail, whose 
shell we have never been able to detect beneath the surface of the 
earth; they are rarely to be found, for they delight in perpetual 
shade. They must have appeared in this country at a late period: 
they are already extinct, unless where the forest has continued in an 
uninterrupted state. 2 2 
~ We have already remarked, that neither species of the snail is to 
be found in the first stratum of clay, nor are they to be seen in the 
_vegetable mould. It is in the range of these strata, the mould and 
’ first clay stratum, making a depth generally of five feet, that the air 
has exerted its influence in decomposing the shells, converting them 
into lime, and the vegetable roots which oceupy this region have con- 
tributed to their farther and more speedy destruction. 2 
INFLUENCE OF CANE BRAKES, cc. - 
If we are asked why the shells are decomposed in this and not in 
the substratum, we answer that we are about to enter upon another 
epoch in our local history :—The visitation of cane (Arundo Missis- 
sippi.) As soon as this vegetable got possession and became matted 
wes 
