﻿106 NEW YORK STATE MUSEUM 



Quality and condition of rock 



The rock of Storm King mountain and of Breakneck ridge at the 

 Hudson river crossing is a very hard granite with a gneissoid 

 structure of variable prominence. The color varies from, grayish 

 to light reddish and the structure is always coarse passing into 

 pegmatite fades that occur as stringers or irregular veinlets. The 

 grayish facies is of slightly finer grain and more gneissoid. Those 

 portions that have been sheared are still darker. There are many 

 joints at the surface running at various angles and an occasional 

 slickensided surface. The mass is cut by several dikes of more 

 basic rock (diorite) of widths varying from a few inches to 8 feet. 

 These dikes are somewhat more closely jointed than the granite 

 and consequently a little more readily attacked by the weather. But 

 where protected they are equally substantial for underground work. 



The chief variation from this condition is where crushing or 

 shearing has induced metamorphic changes. Wherever bed rock 

 has been reached at this point and to such depths as workings have 

 penetrated the rock is of this type. 



The work includes (a) four inclined drill holes from the river 

 margin — two starting from the surface and two from chambers 

 set off from shafts at a starting depth of about 200 feet, (b) several 

 vertical holes in the river itself, and (c) two large working shafts 

 20 x 20, one on either side of the river. 



These give all the data 1 known as to the condition at depth. From 

 them it is apparent that crushing and shearing have been prominent. 

 Many splendid specimens of crush breccia are thrown on the shaft 

 dump. But its present condition at the depth involved is sound and 

 durable. The fractures are rehealed. There has been a recombina- 

 tion of constituents giving a new matrix of complex silicates among 

 which epidote is the most characteristic, while simple decay is of 

 little consequence. For strength and permanence the conditions 

 could not well be improved. There is no reason to apprehend any 

 change for the worse for the reason that the same tendencies must 

 prevail at that depth throughout. It would appear therefore that 

 faulting movements, or the existence of a fault zone of importance 

 can not become a serious obstruction, because of the tendency to 



1 Since this paragraph was written four inclined diamond drill borings 

 have been made from chambers at depths of about 200 feet in the shafts. 

 These have now penetrated the whole distance beneath the Hudson with 

 very satisfactory results. 



