KEPORT ON THIi GEOLOGY OF NORTH AMERICA. 59 



the Ostrea cretacea and Ostreu panda occur also in the ohlei- 

 cretaceous deposits of Alabama." 



" Georgia. — The ferruginous sand appears to abound near 

 Sandersville in this State, whence 1 have received a number of 

 specimens of the Belemnites americaniis." 



"Alabama. — This State presents a vast deposit of both strata. 

 Mr. Conrad informs us that the counties of Pickens, Bibb, 

 Greene, Perry, Dallas, Marengo, Wilcox, Downes, Montgo- 

 mery, and parts of Clarke, Monroe, and Conecute, are chiefly 

 composed of the older cretaceous strata. In Clarke county the 

 nevper cretaceous rock predominates. 



"One of the localities most prolific of fossils is Prairie Bluff, in 

 Wilcox county. The following diagram will convey an idea of 

 its strata : 



Feet 2. Loam. 



2. Ferruginous sand, generally indurated, with Exogyra and Gryphcea. 

 70. Same deposit, in a friable state, with abundance of Oslreafalcata. 

 River bed. 

 " The older cretaceous rock constitutes the long and perpendi- 

 cular bluff at Demopolis, where it has been ascertained by boring 

 to be at least 500 feet thick. The more elevated blcff at Erie 

 is chiefly composed of the same rock, which is here very friable, 

 and well characterized by fine specimens of Pecten quinque- 

 costattis, as well as abundance oi Exogyra costata. A short di- 

 stance north of Erie, the cretaceous rocks terminate, following 

 the course of the Black Warrior ; and at Tuscaloosa the old red 

 sandstone with bituminous coal forms the bed of that river. 

 The Tombeckbe and most of its tributaries run entirely through 

 a region, the substratum of which is the cretaceous group, al- 

 though it is probable that their sources originate in the carbo- 

 niferous limestone, which may extend into the north-east section 

 of Mississippi. We learn from travellers that the cretaceous 

 rocks chiefly compose the countries of the Chickasaws and 

 Choctaws, and it is highly probable that nearly the whole State 

 of Mississippi is of the same formation. It is worthy of remark 

 that all the prairies of Alabama and Mississippi have a sub- 

 stratum of the older cretaceous rock. The newer cretaceous 

 strata prevail only in the southern portion of Alabama, are 

 never covered with a prairie soil, and have not been observed 

 north of the central parts of Clarke and Monroe counties, 



" NummuUte Limestone. — 'After crossing the Alabama river 

 at Claiborne,' says Mr. Conrad, ' I travelled over a level allu- 

 vial country for two or three miles, when the surface became 

 broken by gravelly hills, covered by a pine forest. Near Suggs- 



