200 GEOLOGY OF OHIO 



The average results of these four classes are: 



The shales are seen to be distinctly ahead in this table; while they 

 show slightly more loss than fire-brick in rattling, they also show much 

 better vitrification and much better total strength. 



Also, in examining the composition of the bricks holding the ten 

 highest numbers in the general table, there are seen to be thirteen shale 

 bricks, against three fire-clay bricks, showing that the best material of 

 the state is eighty per cent of it made of shale clay. 



2. Side Cut Material vs. End Cut Material : 



Taking nine samples of repressed bricks made on end cut machinery, 

 whether plunger or auger, and comparing them with twelve side, cut re- 

 pressed bricks, the following figures were obtained: 



Showing a distinct advantage in general average for side cut mate- 

 rial; however, the end cut material in this test was made in many differ- 

 ent kinds of machinery and of very different clay. Separating the va- 

 rious kinds more closely the following figures are obtained: 



End cut material, plunger machines ; 



Three samples made in sewer pipe press and then repressed; 



One sample made in Penfield plunger machine and then repressed; 



(a) End Cut Material, Auger Machines. Five samples, all made c n 

 the Penfield automatic cut off, end cut, auger machine, and then repressed. 



