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 Gobi, in Asia, and similar causes 

 are enlarging the desert of Sahara, in Africa ; where fl'oods of sand 

 are carried upon the wings of the wind, until countries and cities are 

 overwhelmed and lost beneath its accumulating mountains. 



In 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 bkifl:s 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 

 uninterrujDted state. 



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 occupy this region have con- 

 tributed to their farther and more speedy destruction. 



INFLUENCE OF CANE BRAKES, &C. 



If we are aslced 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 



