28 NEW YORK STATE MUSEUM 



as to prevent a more sharply defined expression than this. Much 

 the same conditions are met in the study of similar relationships in 

 Sweden, where the writer in 1910 in connection with the excursions 

 of. the Eleventh International Geological Congress had the oppor- 

 tunity to observe similar phenomena and to discuss their relation- 

 ships with the Swedish geologists. Explanations involving satura- 

 tion with igneous matter, digestion and assimilation alone seem to 

 make possible a reasonable conception of their complex develop- 

 ment. In other areas of the Adirondacks and their borders similar 

 conclusions regarding the complexity of the relations of the Gren- 

 ville with the syenite have been reached. Prof. W. J. Miller 

 describes and maps the " Syenite-Grenville Complex " (Bulletin 126 

 on the Remsen Quadrangle) where the intermingling was too 

 intimate for separation. 



THE PRECAMBRIAN INTRUSIVES 



WITH A CONTRIBUTION BY MAX ROESLER ON THE REACTIONS RIMS 



The anorthosites are far the most abundant of all the rocks in 

 the quadrangle. They are almost entirely made up of plagioclase 

 feldspar, which itself is chiefly within the ranges of labradorite. 

 The rocks were called " hypersthene rock " or " hypersthene " by 

 Prof. Ebenezer Emmons,^ who, however, recognized both the illogi- 

 cal practice of naming a rock after one of its subordinate minerals 

 and also the varying mineralogy. In later years we have applied 

 quite universally to these feldspar rocks the name anorthosite given 

 by Dr T. Sterry Hunt in Canada in 1863. The name implies that the 

 rocks consist essentially or predominantly of plagioclase. Hypers- 

 thene is indeed a rather frequent dark silicate in the masses of 

 labradorite, but we also find with the microscope, hornblende and 

 augite, and we can frequently observe with the eye alone garnet and 

 titaniferous magnetite. The anorthosites have been quite fully 

 described in previous bulletins ^ of the State Museum, as the detailed 

 mapping has proceeded. 



The anorthosites cover practically all but a small part of the 

 Mount Marcy quadrangle. The area of the Grenville rocks and 

 the Syenite series on the north alone extensively interrupt them. 

 There are, however, in addition, some dark dikes of gabbro-syenite, 



1 Report on the Second District, p. 27-30, 1842. 

 ■n W-- ^- S^^J?,'."^' Bulletin on Long Lake Quadrangle, 1907. J. F Kemp 

 iJulletm 138, Elizabethtown and Port Henry Quadrangle p 27-37 



