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NEW YORK STATE MUSEUM 



described, which cast some light on the nature of the Grenville rocks. 

 Others have, however, been noted which are anomalous. On the 

 trail to the summit of the Gothics, inclusions were found by the 

 writer as early as 1898 both at the summit and about 200 yards 

 below it. In 191 5 they were discovered still more abundantly by 

 H. L. Ailing. The one on the summit was about a foot in diameter 

 and appeared to be a mass of gray gneiss, roughly rhomboidal in 

 shape. Under the microscope al:)Out three-fifths of the slide is 

 plagioclase, with the extinctions of labradorite and often micro- 



Fig. 5 Detail of dark, gneissic inclusions in anorthosite, Roaring brook, 



Giant trail 



perthitic. The two-fifths of dark silicates are chiefly hypersthene. 

 •Brown hornblende is subordinate and red garnet occasional. Mag- 

 netite is common. The grain is fine, ranging from 0.1-0.2 mm in 

 diameter. The mineralogy reminds one of the dark rock which 

 appears in the Avalanche lake dike and in at least one other exposure, 



