38 GEOLOGICAL REPORT. [168 



manufacture of fire-brick differs from that of ordinary brick only 

 in this, that it requires more care, both in working the clay and in 

 moulding the brick. Beyond their fire-proof quality, it is 

 demanded of fire-brick that their shape shall be perfect, their mass 

 uniform, and without flaivs in the interior ; also, that they shall be 

 liable to the. least possible shrinkage in a high heat. 



The latter quality is imparted to them by a considerable admix- 

 ture of either sand, or ground fire-brick, to the fire-proof clay, 

 which itself ought to be thoroughly seasoned beforehand, 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 

 convenient moulding. The latter process ought to be performed as 

 in the manufacture of pressed brick, whenever a first class article is 

 aimed at ; for it is only thus that internal and external flaws are 

 entirely avoided. In some localities materials may probably be 

 found which require no further admixture — the strongly siliceous 

 varieties of the clay ; but whenever sand or burnt clay is added to 

 the mass, care should be had that it be free from iron, which would 

 seriously impair the fire-proof qualities of the clay. None but 

 white sand ought to be used. — For the rest, they may be burnt in 

 kilns, like common brick. 



Similar white clays are mentioned by Prof. Wailes as occurring 

 at White Cliffs, Adams county, and near Woodville, Wilkinson 

 county. Of the extent of these deposits, I am not informed. 



68. Cream colored, or yellowish, and gray pipeclays, which assume 

 a faint reddish or pink tint in burning, are perhaps the most 

 common in the Orange Sand formation, especially in the northern 

 part of the State, where it overlies the lignitic strata. 



Most of the clays of the latter formation assume similar tints when burnt 

 though as a general thing they are less refractory — in consequence, probably, 

 of their containing larger amounts of lime and magnesia. The latter substances 

 are copiously contained in the waters issuing from the strata of the formation, 

 last mentioned, while their quantity is extremely minute in those emanating 

 from the Orange Sand strata ; which are themselves as remarkable tor the 

 almost entire absence of these ingredients, as for the universal prevalence of iron. 

 It would seem that the processes ot oxidation and lixiviation which have 

 characterized the Orange Sand, would readily account for the transformation of 

 the dark colored, carbonaceous and magnesian clays of the lignitic strata, int« 



