BRICK CLAYS. 187 



■ The gray shale burns to a denser, harder body than 

 the yellow, and does not blister as easily in burning ow- 

 ing to its lower per centage of iron. 



PAVING BRICKS SHALE, 



COALDALE, ALA. 



A yellowish red, soft shale, with considerable grit. No 

 mica or pyrite noticeable. 



Ground to 30 mesh and mixed with 22 per cent, of 

 water it gave a kan paste, which shrunk 4 per cent, in 

 drying and 5.5 per cent, in burning, giving a total shrink- 

 age of 9.5 per cent. 



The tensile strength of the air dried briquettes was on 

 the average of 25- pounds per square inch with a maxi- 

 mum of 35 pounds. 



Incipient fusion occurs at 1900° F., vitrifioation at 

 2000° F., and viscosity at 2150° F. 



The shale burns to a red body and makes a good red 

 brick. It is also used for paving brick. 



(No. 33.) 

 RED SHALE, 



PEARCE's mills, MARION CO. 



There is an an extensive outcrop of partially weathered 

 Carboniferous shale along the private road of Mr. Pearce 

 just before reaching the millls. It is a red, rather fine 

 grained material, and contains a small amount of mica. 

 Its soft character renders the mining of it an easy 

 matter. When ground the shale gives a moderately 

 plastic ma£s whosfi plasticity could no doubt be in reased 

 by weathering. Forty per cent, of watt r were required to 

 work it up, and the bricklets made from this material had 

 an air shrinkage of 4 per cent. When burned to 2000° 



