TCies — Physical Tests ok Devonian Shales. 



689 



2. The upper and lower surfaces should be preferably ground to true 

 and parallel planes. If this is not done they should be bedded in plaster-of- 

 paris while in the testing machine, which should be allowed to harden ten 

 minutes under the weight of the crushing planes only before the load is 

 applied. 



3. The load should be applied at a uniform rate of increase to the point 

 of rupture. 



4. Not less than an average obtained from five tests on five different 

 bricks shall constitute a standard test. 



It was resolved by the commission that " from the experimental work 

 done so far by the commission, or by others so far as is known to us, in the 

 application of the cross-breaking and crushing tests to paving brick, it is not 

 possible to show any close relationship between the qualities necessary for a 

 good paving material and high structural strength as indicated by either of 

 these tests." 



Extent of New York Shales, together with Tests of Samples from Type 



Localities. 



The shale bearing formations occurring in New York state, beginning 

 with that geologically oldest, are as follows: 



Lower Silurian Hudson river. 



f Medina. 

 Clinton. 

 Niagara. 

 Salina. 

 f Hamilton. 



Devonian , ■{ Portage. 



Chemung. 



Of these formations only the shales of the Salina, Hamilton, Portage 

 and Chemung are at present being utilized. 



Hudson river. This formation is abundantly displayed in the counties 

 of Lewis, Oneida, Montgomery, Schenectady and Columbia. Its tendency is 

 to exhibit siliceous or slaty phases, but in eastern Columbia county it becomes 

 at times argillaceous and at the same time contains considerable iron. 



Medina. The Medina formation at times is shale bearing, as along the 

 (ienesee river, where it is also marly, but the extent of the shaly layers is 

 unimportant, (Hall, Geology of the Fourth District of New York, p. 38.) 

 44 



Upper Silurian -< 



