492 NEW YORK STATE MUSEUM 



The numerous faults are outlined on the map. Their presence is 

 usually indicated by a cliff, but some of the older ones have 

 weathered so as to be recognizable only from a crushed strip. Many 

 of these may have been overlooked in consequence of the dense 

 vegetation and lack of paths or of outlook. 



Shear zones. About three miles west of Graphite are three par- 

 allel gorges with an east-west direction, the largest of which is 

 locally known as the " Ice gorge." These three gorges are estab-' 

 lished along three shear-zones. The nearly perpendicular cliffs of 

 the ice gorge are about 500 feet high, while those of the smaller 

 gorges are about 200. The country rock is a porphyritic gneiss, 

 with large orthoclase phenocrysts in a quartzose ground mass, and 

 containing much biotite. The rock from the sheared zones presents 

 a granulation of constituents with an infiltration of iron oxids. 



Small faults and shear zones are of almost universal occurrence 

 in this region and traverse all types of rock. 



Poliation. This structure is common to all the Precambric 

 rocks, and the general direction of strike is similar. A direction of 

 n. 40 e. is the prevailing one, with low southeast dips. Since the 

 direction of foliation is common to all the rocks, it must have a 

 common origin; since no relation is shown between direction of 

 foliation and any of the intrusives, the structure can not be due to 

 igneous agencies. It appears to result from a thrust from the 

 southeast, while the rocks were still deeply buried. 



A similar and later thrust when they were nearer the surface 

 appears tO' be the cause of the faults. 



Joints. The Precambric rocks are extensively jointed, the joint 

 planes running in all directions. The joints are usually vertical and 

 as a rule only two sets, nearly at right angles tO' each other, are 

 present. Occasionally a third, highly inclined joint is present. 

 Their directions are too inconstant to be reduced to any system. 



PART 4 



Petrography 



It was found difficult to distinguish macroscopically among the 

 basic phases of the three intrusive types — anorthosite, syenite and 

 granite — since with increasing ferro-magnesian minerals they ap- 



