170 WALKS AND TALKS. 



strata go down under the Tertiary, and probably under the 

 Gulf and a portion of the Atlantic. 



There is no proper chalk in the Cretaceous beds of the 

 United States. In the Gulf States, however, is a buffish soft 

 limestone, called the " Rotten Limestone," slightly resembling 

 chalk. As it disintegrates and mingles with vegetable matter, 

 it forms a very rich, black soil. This underlies the very best 

 cotton lands of Georgia, Alabama, and eastern Mississippi. 

 The lower part of the System contains beds of sand interstrati- 

 fied with clays and shales. These convey rain water down and 

 southward from their belts of outcrop. So when holes are 

 bored from the surface down to these water-bearing sands, sup- 

 plies of water are obtained. Hence it is, that at Selma, 

 Cahaba, and throughout the Cretaceous region, Artesian wells 

 abound. 



The Cretaceous rocks of the Gulf States are rich in fossil 

 remains ; often, in riding along the highway, one's eye is ar- 

 rested by some weathered knoll close by the roadside, thickly 

 overstrewn with teeth and vertebrae of sharks and rays of 

 various extinct species as if one were traveling over a sea- 

 bottom. Here also, are multitudes of small and curious oys- 

 ter shells, and many other sorts of shells. Where the rivers 

 and creeks have cut through the Cretaceous strata we find 

 excellent sections. One of the most famous of these is at 

 Prairie Bluff, on the Black Warrior river, in Greene county, 

 Alabama. Here the "rotten limestone" is at the top; then 

 come beds of sand formed evidently, not far from the ancient 

 shore, which lay on the north, just beyond Selma and a little 

 south of Tuscaloosa. These sands contain bits of wood, and, 

 in one instance, I remember seeing the trunk of a tree project- 

 ing several feet from the cliff toward the river. The wood 

 contained a good amount of iron pyrites, but some of it could 

 still be cut with a knife. Here is one layer of cemented sand 

 completely packed with small oysters. How many of these sa- 

 vory bivalves must have gone to waste in those middle geolo- 

 gic ages ! But I suppose they served as food for other ani- 

 mals whose appetites were as worthy of regard as man's. In 



