28 NEW YORK STATE MUSEUM 



quadrangle, where the writer has had the privilege of seeing the 

 critical exposures.^ The syenites are essentially the same kind of 

 rock in both localities and in default of positive evidence which 

 may appear at any time within the present area, this relationship 

 is assumed. 



The anorthosites were called by Professor Ebenezer Emmons in 

 his extremely valuable Report on the Second District, ** h}'pers- 

 thene " or '" labradorite rock/' but inasmuch as the hypersthene is 

 very subordinate and as neither of these is a good rock name, the 

 term first employed by Dr T. Sterry Hunt in Canada, is here pre- 

 ferred, as it is generally by geologists today. 



The anorthosites vary from almost pure aggregates of plagio- 

 clase crystals through variations caused by increasing amounts of 

 a pyroxenic component. The commonest of the pyroxenes are 

 hypersthene and green augite, the latter on the whole being perhaps 

 more abundant than the former. ^lore or less titaniferous mag- 

 netite also appears. The rocks are normally \ery coarsely crystal- 

 line. In the central portion of the great masses, feldspar cr}'stals, 

 apparently not connected with peginatite veins may sometimes be 

 seen as large as a man's hand. Cr\-stals two or three inches across 

 are not uncommon. Well cr\-stallized and uncrushed specimens are 

 rare. The entire area has been subjected to such severe pressure 

 and granulation that the outer borders of the crystals are almost 

 always crushed to a finely granular and whitish mass. Within this 

 rim the bluish nuclei of the plagioclases remain. \Mien shearing 

 and dragging has been added the nuclei yield augen-gneisses of the 

 most typical and instructive kinds. The crushing may go so far 

 as to destroy all nuclei and leave a whitish or greenish pulp of 

 secondar}- products. This is closely akin to saussurite. When 

 weathering is added the rocks are often extremely white on ex- 

 posed surfaces, appearing almost as if whitewashed. 



The plagioclase crystals sometimes assume elongated forms and 

 suggest a coarse diabasic texture when there is sufficient of the 

 dark silicates to bring this out. Rarely the plagioclase exhibits the 

 characteristic irridescence of certain labradorites. It has not been 

 noted in this quadrangle but in the ]Mt ^Marcy group it is not un- 

 common in the beds of brooks, where either from pebbles, by 

 chance properly cut, or from the smooth bed rock the irridescence 

 flashes out to the obser\'er. 



1 Gushing, H. P. Geology of the Long Lake Quadrangle. X. Y. State 

 Miis. Bui. 115. 1907. p. 481. 



