188 II. r. CUSHING AUGITE-SVEXITK GMiISS NKAll LOON LAKE 



the rock which constitutes mount Defiance, near Fort Ticonderoga, with 

 these S3^enites, and inspection of his specimens and slides full}' confirms 

 the suggestion. Here also hornblende is more prominent than at Loon 

 lake, but the characteristic augite is also consi)icuous. Allanite occurs 

 here likewise.* 



nia TlJl'l'EU LAKE 



Rocks which are at least in part to be classed with these augite-syenites 

 are excellently exposed along the shores of Big Tupper lake and extend 

 widely to the north and east. They are closely involved with red gra- 

 nitic gneisses wliich equal them in extent and into which they grade. 

 Together with these are other granites, of whose relations nothing can 

 be said, as no contacts have been seen. 



• Relationship to the Anorthosites 



The main interest attaching to the Tupper Lake syenite lies in the 

 evidence it may be expected to furnish concerning the relations of the 

 syenites to the anorthosites. A large area of anorthosite in southern 

 Franklin county, in the heart of which the Saranac lakes lie, is sur- 

 rounded by the Tupper Lake syenite on the south and west. 



It may be said, in the first place, that the syenite cannot differ greatl}' 

 in age from the anorthosite, having been intruded into the Grenville rocks 

 and subsequently metamorphosed under the same conditions as to load, 

 as shown by the character of the metamorphism. Again, their areal dis- 

 tribution indicates consanguinit3\ Further, the identit}' of many of the 

 minerals in them and in the granitic gneisses as well combines to render 

 it strongly probable that all have resulted from a common magma. 



With such ideas in mind, a series of traverses were attempted from 

 one to the other, which were unsatisfactory, owing to a lack of outcrops 

 at the more crucial points. In some cases a blending of one rock into 

 the other seems apparent in the field. The anorthosite becomes much 

 crushed and very gneissoid near the peripheral parts of the mass, the 

 blue labradorite-augen showing constant decrease in number and eventu- 

 ally disappearing entirely. Wiien fresh these crushed rocks are much 

 like the syenite in color and appearance, and Aveather into brown gneisses 

 the exact counterparts of the weathered syenites, so that it is impossible 

 to tell when the passage from one rock to the other is made, but the thin- 

 sections do not wholly bear out the idea of such a blending. Anortho- 

 sites are found which contain both orthoclase and quartz, denoting an 



*J. F. Kemp: Rep. State (ti'oI. N. Y. Isir., pt. i, p. irrl. 



