IPo s t e Is t a 327 



down. The transformation of the accumulated,, 

 rounded grains into a crystalline, orderly mass 

 was not accomplished in one geologic epoch but 

 in many. That heat could have played no un- 

 usual part we do certainly know; pressure play- 

 ed a part, because where the topmost laminae of 

 the formation had been laid upon each square 

 foot of sea bottom, at Providence Cove i,ooo- 

 tons rested, a load for a freight train of twenty 

 cars. Time is represented in a series of results 

 otherwise very difhcult to comprehend. If frag- 

 ments be broken, the ring is sharp and clear. 

 The material is so clear of impurities that every 

 piece is attached to its neighbor in the most 

 intimate crystalline contact. 



Much variation in this crystalline condition 

 can be noted. At Providence Cove the rock 

 seems throughly indurated. This is not due 

 alone to the fact that thousands of feet more of 

 sediment was laid upon it than upon the beds at 

 the Station, but in part to a difference in the 

 mineral and chemical composition of the sedi- 

 ment itself. Here is more silica as well as more 

 uniformity in composition. Under a great 



