GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK I7. 



asunder, and these small seams of ore had been forced up from the 

 main mass below" (p. 559). "The phenomena of the mmes in 

 many places on this vein (the Phillips vein) induce the idea of 

 igneous injection, connected with a powerful upheaving force. The 

 feldspar is often pearly, wrinkled, and with bent laminae. The 

 appearance of hyalite, a mineral usually associated with volcanic 

 and trap rocks; the apparent injection in veins among the seams 

 and crevices of the rock; the appearance of softening of the gneiss 

 and bending of its layers like flowing slag, seem to point to an igne- 

 ous origin of this vein" (p. 564). 



Such statements show an extraordinary grasp of the processes 

 which formed the Highland rocks, and it would be difficult even 

 with the newer phraseology, after nearly 80 years of development 

 of geologic science to describe the salient features better or to paint 

 the minor structural peculiarities as well. 



Mather's description of the larger structural features of the 

 Highlands also is worthy of note. 



" The Highlands in Rockland and Orange are a continuation of 

 those of Putnam and Westchester counties, and are similar in general 

 aspect, in the kinds of rocks, and in their mineral products. The 

 rocks consist of gneiss, and hornblendic gneiss, syenite, granite, 

 limestone, hornblende, serpentine, augite and trappean rocks. The 

 strata dip to the southeast at angles from fifty to ninety degrees, 

 but there are localities where the strike and dip are transverse to 

 the general directions. The strata are intersected by seams trans- 

 verse to the direction of the strata, and nearly perpendicular to the 

 line of bearing, and at intervals of one hundred to ten thousand 

 yards. Dislocations and vertical and lateral heaves have occurred 

 along many of these lines of fracture. The outcropping edges of 

 the strata are not parallel to the line of bearing, but like the ridges, 

 slope gradually down to the northeast; while on the southwest, 

 steep escarpments range along the lines of faults. Many of these 

 faults are upon an enormous scale, and render the tracing of narrow 

 beds of rock of economical value a matter of no small difficulty. 

 There are no continuous ridges of mountains of more than a 

 few miles in length, in consequence of the interrup^^ions caused by 

 dislocations and lateral heaves of masses of the strata. The hills of 

 similar rocks succeed each other in echelon lines, which seem to 

 have been caused by lateral heaves along the lines of fault. In 

 consequence of this, neither the line of outcrop nor the line of 

 bearing is parallel to the general direction of the Highlands, but 



