50 NEW YORK STATE MUSEUM 



Granite. While rocks of granitic composition have been observed 

 they seem to be so closely connected with the syenite series as to be 

 mapped with them. On Scott's Cobble along the northwestern edge 

 of the sheet this is true. There are, however, in the bed of the East 

 branch in the Grenville area on the northern border, some very nar- 

 row dikes of pink granitic rock which traverse the old Grenville 

 sediments and merely deserve passing mention. There is also a very 

 small exposure of red granite on the east pass of Baxter mountain, 

 where the two branching trap dikes are mapped. The granites do 

 not constitute a sufficiently large member in the local geology to 

 receive a special color on the map. 



Gabbro-syenite of the basic gabbro series. In the summers of 

 1888, 1889 and 1890 the writer was in the field accompanied by V. F. 

 Marsters studying the trap dikes of the Champlain valley and neigh- 

 boring mountains.^ Having read in Prof. Ebenezer Emmons's 

 Report on the Second District, page 215, of the great trap dike at 

 Avalanche lake,^ we made a trip into the mountains to visit it. As the 

 dike lies in a steep-walled gorge between the main mass of Mount 

 Golden on the south and its northern shoulder, sometimes called 

 Avalanche mountain, it impressed the writer as a mass of sheared and 

 dynamically metamorphosed rock in a faulted zone. It was there- 

 fore described as " The great shear zone near Avalanche lake in the 

 Adirondacks," in the American Journal of Science, August 1892, 

 pages 109-14. The contrasted mineralogy of the dike when com- 

 pared with the anorthosite walls was thought to be due to crushing 

 and recrystallization. The decided abundance of garnet, which was 

 considered a metamorphic mineral, and the finely crystalline, granu- 

 lar nature of the rock gave some color to the view. Mineralogically 

 the dike consisted of predominant, irregular and rather fine-grained 

 hypersthene, augite, garnet, hornblende and magnetite, with less 

 abundant plagioclase and orthoclase, all showing crushing. The 

 neighboring walls are coarsely crystalline anorthosite. At this time 

 the writer was familiar with the diabase dikes of the mountains and 

 with the trachytic and rare basaltic rock types in the dikes of the 



^ The results found publication as Bulletin 107, of the U. S. Geological 

 Survey, 1893. 



2 Even earlier mention of the dike is made by W. C. Redfield in " Some 

 Account of Two Visits to the Mountains of Essex Co., N. Y., 1836-37," 

 Amer. Jour, of Science, ist series, 33:301. On one of these expeditions, both 

 of which were undertaken to examine the iron ores of Lake Sanford, James 

 Hall accompanied Mr Redfield. Professor Emmons was with him on the 

 other. Interest in the iron ores was very keen at the time. Professor 

 Emmons describes the dike also in the Second Annual Report, N. Y. State 

 Survey, 1838, p. 225, Atlas, pi. 4. 



