14 NEW YORK STATE MUSEUM 



ward into the younger strata, where they show features that leave 

 their age unmistakable. 



Doubtless in some cases what now appear to be reversed faults of 

 moderate displacement within the gneisses, or along contacts, are 

 truncated thrusts of large size. This inference is borne out by the 

 presence of large thrusts in the Paleozoics at the north. 



It would appear that not only did distinct normal fault breaks 

 occur as the result of adjustments following the elevation of the 

 Green mountains, but that normal slips occurred along the planes 

 of the earlier thrusts. 



This feature is best shown in the relations now existing between 

 Bald hill and the Mount Honness spur, and in similar ones between 

 Shenandoah mountain and the mass of gneiss at the east of it. In 

 these two instances the Paleozoics have clearly been dropped back 

 between the gneiss spurs with a large throw on the west, marked 

 in one case by the scarp on the east of Bald hill, and in the other by 

 that on the east of Shenandoah mountain. 



The two spurs in each case tended to act as a single block. The 

 normal fault intersects the thrust at an acute angle forming a tri- 

 angular valley narrowing southward. Some backward movement 

 along the thrust plane must have accompanied the slump, Dimin- 

 ishing tension faulting eastward is marked by small scarps on the 

 west of the Honness spur but is not noticeable on the eastern gneiss 

 mass. 



The Hook spur shows these features imperfectly developed. 



PETROGRAPHY 



General. The gneisses show much similarity in their mineralogy. 

 Distinctive characters are furnished by the structure, the preponder- 

 ance of some minerals, or the degree of alteration in the rock. A 

 few composite types may thus be defined. It will be convenient 

 to describe these first, while the variations in many instances may 

 best be indicated in discussing their outcrops. The thin sections 

 may be reviewed as a whole later. Possible ancient surface altera- 

 tions must always be carried in mind. 



Bald hill granite gneiss. This rock is prominently developed 

 within and south of the quadrangle. There is great uniformity in 

 its general color, mineralogy and texture. It shows a few variations, 

 but as a whole is remarkably homogeneous. In outcrops it is com- 

 monly drab colored and granitelike in appearance. The thin sec- 



