634 PETROLOGICAL ABSTRACTS AND REVIEWS 



an intruded gabbroid magma, developing a chilled gabbroid border fades and 

 an upper zone of anorthosite from a magma which was to a very considerable 

 degree at least, actually molten. The anorthosite-gabbro and gabbro associ- 

 ated with the anorthosite represent local differentiates. Syenite and granite 

 are not differentiates from the anorthosite, although transition rocks (Keene 

 gneiss) were produced locally by magmatic assimilation of stiU hot, but not 

 molten, anorthosite by the syenite or granite magma. 



Miller, William J. " Geology of the Schroon Lake Quadrangle," 

 Bull. 21^, 214, N. Y. State Mus., 1918 (1919). Pp. 102, map i, 

 pis. 14, figs. 9. 



The Schroon Lake quadrangle represents an area of about 215 square miles 

 in the central eastern portion of the Adirondack mountain region. The oldest 

 rocks are those of the Grenville series which were intruded by a relatively stifiE 

 gabbroid magma which differentiated and formed the anorthosite. The intru- 

 sion of the anorthosite lifted the Grenville strata but also engulfed fragments of 

 it. Following this came the intrusion of the syenite-granite series which par- 

 tially domed, partially broke and tUled, the Grenville. The metamorphism of 

 the Grenville took place probably before or during the period of igneous 

 activity. During the succeeding period of uplift there was great erosion and 

 some igneous activity indicated by the intrusion of certain diabase dikes. In 

 late Cambrian time a gradual submergence took place with deposition of sand- 

 stones and dolomites. A long period of erosion from Ordovician to late in the 

 Mesozoic reduced the land to a peneplain rising to moderate heights above the 

 general level, and this was followed by uplift and active erosion, which con- 

 tinues to the present time. During the Ice Age the entire area was covered by 

 the ice sheet. Toward its close there was a subsidence of several hundred feet 

 below the present level, and finally a diJBferential uplift with greater elevation 

 at the north. 



Miller, William J. '^ Banded Structures of the Adirondack 

 Syenite- Granite Series," Science, XL VIII (1918), 560-63. 

 Both assimilation and differentiation contributed to the banding. 



Miller, William J. ''Silexite: A New Rock Name," Science, 



XLIX (1919), 149. 



The name silexite is proposed for any body of pure or nearly pure silica of 

 igneous or aqueo-igneous origin which occurs as a dike, segregation mass, or 

 inclusion within or without its parent rock. (See also "Pegmatite, Silexite, 

 and ApUte of Northern New York," Jour. Geol., XXVII [1919], 28-54.) 



