CRETACEOUS FORMATION. 87 



they shall be liable to the least possible shrinkage in 

 a high heat. The latter quality is imparted to them 

 by a considerable mixture of either sand or ground 

 fire brick to the fireproof clay, which itself ought to 

 be thoroughly seasoned before, and then well worked 

 up with such additions of the above materials as may 

 be required. In judging of the amount of sand or 

 ground brick to be added, it is to be observed, as a 

 rule, to add as much as may be consistent with the 

 proper firmness of the burnt brick and with conve- 

 nient moulding. The latter process ought to be per- 

 formed, as in the manufacture of pressed brick, when- 

 ever a first-class article is aimed at, for it is only thus 

 that external and internal flaws are entirely avoided. 

 In some localitdes materials may be probably found 

 which require no further admixture — the strpngly sili- 

 ceous varieties of the clay; but whenever sand or 

 burnt clay is added to the mass, care sliould be had 

 that it be free from iron, which would seriously im- 

 pair the fireproof qualities of the clay. None but 

 white sand should be used. For the rest, they may 

 be burnt in kilns like common brick." 



RUSSELL AND MACON COUNTIES. 



Within .the limits of Girard and Phoenix Citj, op- 

 posite Columbus, and in the hills to the west of Gi- 

 rard, are many exposures of the Tuscaloosa strata, 

 aggregating some 200 feet in thickness. These are 

 composed mainly of sands, but there are numerous 

 beds of whitt., gray and purple or mottled clays inter- 

 stratified with the sands. The small stream which 

 fiows through Girard exposes a number of these clay 

 beds, and others are to be seen in the hills to the west 

 of ;the town. The materials for the manufacture of 



