r90 NEW YORK STATE MUSEUM 



retreats. It seems quite probable tliat all the biotite in these 

 rocks lias resulted from the alteration of hornblende during 

 metamorphism, in which case its abundance in this specially 

 mashed and stretched rock is quite what would be expected. 

 There is from 15'^ to 20^^ of quartz in the rock, mainly in leaves 

 and lenses as usual. The rock quite plainly belongs with the acid 

 syenites such as no. 4 and is merely an extra-stretched representa- 

 tive. The original crystals from whose mashing the present 

 augen have been derived were of much larger size than in any 

 other of the red rocks seen. 



The augen gneiss at the east, near the fault (no. 11) is more 

 basic than any of the foregoing, though clearly belonging with 

 them. It contains some ZO^t of dark silicates and not more than 

 10^ of quartz. Augite, bronzite, hornblende, magnetite and 

 garnet are all present, and there are also a few fragments of 

 what appears to be brown hornblende, but the identification is 

 not certain. The garnet is usually idiomorphic, though one or 

 two instances of corrosion rims around magnetite occur. Apatite 

 and zircon are abundant and often of large size. So far as these 

 minerals go, the rock is precisely like the ordinary Adirondack 

 gabbro, except for the zircon. But there is considerable quartz 

 of the usual flattened type, and the feldspar is mainly of the 

 indefinite microperthite or else of a curious and striking micro- 

 graphic sort of intergrowth. There is in addition some little 

 plagioclase, whose extinction angles would indicate a basicity at 

 least that of andesin and som:^ micropegmatite. The quartz and 

 feldspar are therefore quite as in the previous rocks. The meta- 

 morphism, however, has not been so severe. The rock must 

 approach to monzonite in composition. 



The slide of the more basic, blackish syenite (no. 10) is from 

 the rock at the quarry, near the top of the hill and less than -J 

 mile from the fault line. The exposures are excellent here and 

 «how fine grained, thoroughly gneissoid rocks, both the green and 

 black phases being present in quantity and grading into one 

 another. The green rock is identical with the syenite at the 

 village (nos. 1 and 2) except in the lack of feldspar augen and in 

 being a trifle more basic. 



