24 CRETACEOUS GROUP 
white and friable, and so much resembles chalk that it is 
not surprising that it should have been mistaken for the 
real chalk of commerce, from which it differs in possess- 
ing a coarser and more granulated structure, and in con- 
taining a considerable proportion of argillaceous earth.’ 
MISSISSIPPI. 
This state has an extensive marl tract in the Chickasaw 
fields, near the borders of Tennessee. The charac- 
teristic fossils have been sent to me by my friend Mr. 
Brewster. In the Choctaw country similar fossils are 
also very abundant. 
TENNESSEE. 
The south western portion of Tennessee represents a 
continuation of the tract just mentioned, which takes a 
westerly direction across the Mississippi river at the 
Chickasaw Bluffs. 
LOUISIANA. 
Dr. Pitcher, in a recent letter, describes an extensive 
deposit of Ferruginous sand between Alexandria and Na- 
chitoches. Judge Bry has also noticed it near the town- 
ship of Wachita, on the Wachitta river, where it is re- 
cognized by Belemnites, Ammonites and Gryphza. 
ARKANSAS. 
Mr. Nuttall long ago found fossils of this formation on — 
the calcareous platform of Red river, above and below the 
a vel 
