120 GEOLOGICAL SURVEY OF ALABAMA. 



INDUSTRIAL MATERIALS. 



Among the industrial materials found in this valley, 

 brick clay, porcelain clay, limestone, building rock, fire-proof 

 rook, and glass sand, are the most prominent. 



BRICK CLAY. 



Clay suitable for making building brick exists in many 

 places. On nearly all the low lying or bottom lands a stra- 

 tum of fine yellow clay, 'several feet thick, is found just be- 

 neath the surface. Especially is this the case along all the 

 streams that flow in from the coal measures. These streams 

 have silted down along their course a bed of yellow clay of 

 very fine quality. It is free from chert or gravel, or par- 

 ticles of iron ore, which are hard to eliminate and which are 

 always injurious to the brick, if worked in. 



There are very many beds of clay belonging to the Cam- 

 brian Limestone formation. It is generally yellow, some 

 places in great quantity. This is the ordinary flat woods 

 yellow clay. It is native to that formation, and is found in 

 all of our deep Silurian valleys. In some places it affords a 

 good brick clay, but generally contains fine gravel, pieces of 

 chert, and much iron oxide. These cannot be got rid of, and 

 consequently the bricks made from it are rough and not of , 

 uniform texture or strength. The iron oxide generally con- 

 tains sulphur, and this with the iron results in blistering and 

 rapid decay. Such bricks will not make a smooth, strong, 

 or durable wall. Much of this kind of clay has been used 

 for making brick in the vicinity of Birmingham, and used in 

 building the city. But used only because the market did 

 not afford a better material, at a reasonable cost. Such 

 bricks would not be sold to intelligent builders, if brought 

 into competition with others free from their defects, and of 

 uniform strength and texture. 



