44 NEW YORK STATE MUSEUM 



affinities of the rock are rather with the anorthosites than with the 

 basic gabbros. 



The relations of this rock to the other eruptives and the sedimen- 

 taries have been nowhere shown as the exposures were so Hmited 

 that no conclusion could be drawn. The rock is one admirably 

 adapted to give pronounced hornblendic gneiss under shearing and 

 stretching and it may have been the original of some of the puzzling 

 gneisses occasionally seen in the region. Under metamorphism the 

 augite would pass into hornblende and the relations of it to the 

 feldspar are exactly those which would yield interleaved lenses 

 when crushed and drawn out. 



Syenite series , 



The syenitic series has been one of comparatively late recognition 

 in Adirondack geology. The rocks were first identified as eruptives 

 on the western side of the Archean area by C. H. Smyth.^ Soon 

 thereafter the significant exposures found by H. P. Gushing in the 

 railway cut near Loon Lake station on the northern side demon- 

 strated their intrusive relations with the Grenville.^ 



The writer has also noted briefly the occurrence of green gneisses 

 in Ticonderoga which were suspected of being eruptive/ but it 

 was only after an instructive trip with Professor Gushing to the 

 Loon Lake occurrence that the identity of these rocks was demon- 

 strated. At times they look much like anorthosites especially in 

 their crushed and gneissoid phases, and again they have been 

 classed with the supposed ancient gneisses. The series embraces 

 variations from the typical composition of syenite but the minerals 

 with minor additions are the same and there are intermediate 

 phases. As components of the Adirondack area the syenites do not 

 yield in importance, even to the anorthosites, and their recognition 

 has served to remove a vast amount of hitherto puzzling rocks from 

 the noncommittal designation " gneiss." 



In typical and least altered form the syenite is a dark green 

 massive rock, of moderate coarseness of grain. Its components 



1 Smyth, C. H. jr. Crystalline Limestones and Associated Rocks of the 

 Northwestern Adirondack Region. Geol. Soc. Am. Bui. 6. 1895. p. 271- 

 83. Report on the Crystalline Rocks of the Western Adirondack Region. 

 N. Y. State Geol. 17th An. Rep't, p. 472. 



2 Augite-syenite Gneiss near Loon Lake, N. Y. Geol. Soc. Am. Bui. 10. 

 1899. P- i77~92. Geology of the Northern Adirondack Region. N. Y. 

 State Mus. Bui. 95. 1905. p. 312; Bui. 115. 1907. p. 512. 



3 Preliminary Report on the Geology of Essex County. N. Y. State Geol. 

 An. Rep't for 1893. 1894. p. 452. 



