BRICK OLA78. 185 



of paving brick, partly because many of them contain 

 about the right quantity and kind of fluxing impurities, 

 and also because, owing to the fineness of grain, they vit- 

 trify more evenly and thoroughly. 



Paving brick are at times made from fireclay, and the 

 results obtained are excellent, but still shale is the favored 

 mateiial. 



Except for comparing brick made from the same 

 deposit, the color is absolutely no indication of the quality 

 of a paving brick. 



The important properties which a paving brick should 

 show are low absorption (under 2 per cent.) and resistance 

 to abrasion. Crushing strength is of little importance 

 provided it exceeds say 8,000 pounds per square inch. 



The brick clays described below come from several 

 geological formations. The Graves' shales, Nos. 107 and 

 108 ; the Coaldale shale aud the Pearce Mill shale, No. 3, 

 are Carboniferous shales. The Dixie clay and No. 128 

 and 129 of Mr. Stevens, are from the Poleozoic limestones, 

 while the rest, No. 110 from Shirley's Mill, No. 122 from 

 Chalk Bluff, Elmore Co.; No. 126 of Mr. Stevens, from 

 Woodstock ; No. A, from Tusealoosa Co., are from the 

 Tuscaloosa formation of the Sower Cretaceous. 



(Nos. 107 and 108.) 

 BRICK-SHALES. 



W. H. GRAVES, BIRMINGHAM, JEFFERSON CO. 



Associated with the coal on the property of Mr. W. H. 

 Graves are two beds of shale, viz: a yellow, sandy shale, 

 and a gray one containing much less grit. Both of these 

 were tested physically and the results of these tests are 

 given below. The yellow shale contains a high per cent- 



