30 NEW YORK STATE MUSEUM 



exhibited are one-fourth of a mile southeast of The Flume; on the 

 mountain side one-fourth of a mile northwest of High fall ; a long 

 wide belt one-half to i mile west of Upper Jay; and along the 

 northwestern base of the Sentinel range. In some places there are 

 locally developed, without sharp boundaries, within the Marcy 

 anorthosite masses of rock which are quite certainly to be classed 

 with the Whiteface type and vice versa. Only two such masses are 

 represented on the geologic map, one on the Mt Whiteface trail 

 near Marble mountain, and the other on the mountainside 1% 

 miles east-southeast of Owen pond. 



As already shown, the Marcy and Whiteface types are very 

 closely related in chemical composition, which strongly supports 

 the view that the two are differentiates of the same magma. 

 In the writer's paper^ already referred to evidence is presented 

 in support of the view that the whole body of Adirondack anortho- 

 site is best to be regarded as a direct derivative of a laccolithic mass 

 not much greater across than the area of its present outcrop ; that 

 the anorthosite differentiated practically in situ from an intruded 

 gabbroid magma; that the anorthosite crystallized from the upper 

 or residual portion of the magma during and after the sinking of 

 many of the f emic constituents ; and that the Whiteface anorthosite 

 developed both as an outer and an upper, somewhat more gabbroid, 

 marginal facies of the anorthosite. Gushing^ maintains that the 

 gabbroid (Whiteface) facies developed as an oiUer chilled border 

 of the anorthosite. His argument seems so conclusive that it is 

 unnecessary to repeat it here. But, in this connection, it should be 

 noted that the borders of the anorthosite body have in some dis- 

 tricts, like the Lake Placid and the Schroon Lake quadrangles, been 

 so cut out or cut to pieces by the later syenite-granite intrusions 

 that the full original extent of the anorthosite is not now shown. 



The writer believes further that the chilled gabbroid (Whiteface) 

 border facies also developed as an upper limit which formerly 

 existed as a cover resting directly on the whole great mass of 

 anorthosite rather than merely as an outer Wmit, as Gushing suggests. 

 Thus, the Whiteface anorthosite of the Lake Placid quadrangle does 

 not exist merely as a definite fringe around the outer margin of the 

 Marcy anorthosite. Typical Whiteface anorthosite occurs fully 

 14 or 15 miles within the present border of the anorthosite area, 

 and inclusions in the syenite-granite series outside the general 

 anorthosite area show that the Whiteface anorthosite formerly ' 



^ Geol. Soc. Amer. Bui., 29:399-462, 

 2 Jour. G?ol., 1917, 25:506. 



