698 



Report of the State Geologist. 



per cent, in drying and 5.3 per cent, in burning. The tensile strength of 

 the aii-dried mud per square inch was on the average thirty-four pounds, 

 w ith a maximum of thirty-nine pounds. 



Incipient fusion occurs at 1,900° F., vitrification at 2,050° F., viscosity 

 at 2,200° F. 



The shale burns to a dark red. It is used in the manufacture of paving 

 brick. 



The composition of the clay, from an analysis furnished by the Hornells- 

 ville Brick Company, is as follows : 



Silica 64.45 



Alumina 17.77 



Ferric oxide 7.04 



Lime .58 



Magnesia 1.85 



Potash 2.52 



Soda . . 1.95 



96.16 



Fluxes 13.94 



The method of manufacture followed at these works consists of the usual 

 dry-pan for grinding the shale and wet-pan for tempering it. The molding is 

 done by stiff-mud, side-cut machine, and the green brick are repressed. The 

 burning is in down-draught kilns. 



From the tests cited above it will be seen that the shales used compare 

 very favorably with the requirements of a paving-brick material. Most of 

 them are slightly more siliceous than the average run of paving-brick clays, 

 but this is no serious objection. 



The lean character of many can be overcome by the addition of plastic 

 day, as in the case of the Cairo shale, in which instance the mixture, as 

 already stated, had a tensile strength of one hundred pounds per square inch. 



The amount of fluxes present permits of their vitrifying at comparatively 

 low temperatures. But if necessary their refractoriness could be easily 

 increased by the addition of a certain amount of fire-clay. 



Most of the shale deposits are easily accessible and located in close prox- 

 imity to railroads. 



