14 NEW YORK STATE MUSEUM 



than feldspar rise to 12 per cent, and the rock should be classed 

 with the anorthosite-gabbro phase of the great anorthosite area. 



The rock is light gray, moderately gneissoid, and usually highly 

 granulated except for occasional large (i inch), dark blue labrador- 

 ite crystals svhich remain as ungranulated cores. As Gushing 

 states,^ the lighter colored granulated feldspar has plainly originated 

 from the crushing of the large dark blue feldspars. 



This mass of anorthosite is farther separated from the great area 

 in Essex and Franklin counties than any other so far discovered, 

 the small area at Rand Hill in Clinton county being the next most 

 distant. According to Gushing- the anorthosite is younger than, 

 and intrusive into, the Grenville but older than the syenite. 



Syenite 



An exceedingly variable series of rocks is comprised under the 

 term syenite as here considered. From a normal or typical mod- 

 erately quartzose syenite, the variation is to a granitic syenite on one 

 hand and through to almost gabbro on the other. For the sake of 

 convenience the normal syenite will be discussed first and then the 

 basic and acidic phases, though it must be clearly understood that 

 these variations of the syenite mass are in no sense sharply separable. 



Normal syenite. What is regarded as normal syenite occupies 

 fully one-third of the area of the quadrangle or about 75 square 

 miles. It is the most extensive rock of the region. It is almost 

 invariably moderately quartzose, the average amount of quartz 

 being 10 to 15 per cent. When the quartz content runs higher than 

 20 per cent the rock is no longer regarded as normal syenite. ]\Iore 

 or less plagioclase (5 to 25 per cent), generally oligoclase to andesine, 

 is also always present. When quartz is absent and the lime-bearing 

 feldspars exceed the alkali feldspars, the rock is classed with the 

 basic phases of the great syenite mass. Microperthite is rarely 

 absent and ranges in amount from 10 to 16 per cent. From 10 to 

 25 per cent of orthoclase generally occurs. From 8 to 20 per cent 

 of pale green augite with good cleavage occurs in two-thirds of the 

 slides examined. Hypersthene was noted in but one slide. Horn- 

 blende (deep green to yellowish green) is almost always present in 

 amounts up to 15 per cent. Small percentages of magnetite, zoisite, 

 and zircon never fail. Small amounts of garnet and apatite occa- 

 sionally appear. One slide shows a few grains of epidote. These 



IN. Y. State Mus. Bui. 95, p. 305. 

 2N. Y. State Mus. Bui. 115, p. 480-81. 



