GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 45 



trated in certain zones along which remarkalble deformational effects 

 are recorded. Some of the most elaborate transformations take the 

 form of shearing, granulation and recrystallization (see plate 40) ; 

 and where the conditions are not so favorable for this minute struc- 

 tural effect, crush zones are developed with completely recemented 

 crush-breccias. Such products have been secured from the Storm 

 King granite, indicating deformation of this formation under rather 

 deep-seated conditions. 



All stages of dynamic disturbance are recorded in these rocks, 

 from strain of the constituent minerals observable only in the 

 microscope to completely mashed material. Recent experience in 

 connection with certain engineering projects indicates that these 

 strain effects are accumulated to great intensity along certain belts 

 and that at considerable depth beneath the surface, in deep shafts 

 and tunnels, these overstrained zones develop the peculiar " popping 

 rock." This seems to be the result of the disturbed equilibrium pro- 

 duced by removing part of the original support of the rock in these 

 excavations. In such places new slabs break off along lines quite 

 independent of the other structural lines of the rock and in the 

 most pronounced cases add much to the danger and difficulty of 

 deep underground working. (See discussion of Hudson River 

 crossing in the chapter on engineering geology). 



The zones which have shown excessively strained conditions at 

 depth are prdbably represented at the surface by the close-set parallel 

 joints or sheeted structure that is repeatedly observed in all the 

 massive rocks. A region where the most substantial rocks have 

 such a condition irregularly distributed can hardly be considered to 

 have reached any very high degree of stability. It is either 

 accumulating additional strained condition, which may ultimately 

 overcome the strength of the rock and require readjustment, or else 

 it is a remarkably well-preserved residue of much older dynamic 

 impressions still held in the most massive rocks. Molecular read- 

 justment is doubtless going on, but the normal resistance to such 

 reorganization in the most massive rocks may account for all this 

 lagging of deformation. 



Formational groups of larger petrographic significance 



The more important rock classes representative of the great variety 

 which actually occurs are the following: 



a Sedimentary and organic rocks (little metamorphosed) 

 b Sedimentary and organic rocks (much metamorphosed) 



