316 NEW YORK STATE MUSEUM 



quartz diminishes, but it does not disappear, and the plagioclase 

 remains acid, albite to oligoclase, instead of the labradorite of 

 the gabbros. The affiliations of the rock therefore remain with 

 the syenite, and it does not become a true gabbro. Chemical 

 investigation brings out the same features, as will be later 

 shown. 



Of equal interest is the passage of this syenite into a red 

 gneiss. In one direction the passage is into a finely granular red 

 gneiss, which Smyth states to differs from the main rock only in 

 a more complete granulation of the constituents, the formation of 

 a little hematite, which causes the color change to red, and an 

 increase in the amount of quartz. In another direction the tran- 

 sition is into a coarser red gneiss which contains a conspicuous 

 amount of hornblende. 



Besides these important evidences of great variation in the 

 syenite mass, the Diana area is noteworthy in yet another respect. 

 It borders a long belt of (jrenville rocks for several miles; and 

 Smyth has presented in great detail the perfectly clear evidence 

 that it cuts the Grenville rocks intrusively, since it contains 

 abundant inclusions of them, and since it cuts them out along 

 the strike.^ These relations are here shown in greater perfection 

 than in any other locality so far described in the Adirondack 

 region, and seem to the writer to show not only that the syenite 

 is younger than the Grenville rocks, but also that it is considerably 

 3'ounger. The less severe metamorphism which it has suffered, as 

 evinced by the considerable extent to which it retains original 

 textures which definitely show its igneous character, when com- 

 pared with the completely crushed and recrystallized condition of 

 the Grenville sediments and associated igneous gneisses, as well as 

 with much of the Saranac gneiss, would seem to demonstrate 

 this clearly, and to show that, so far as age is concerned, their 

 condition of metamorphism would require their classification with 

 the anorthosites, rather than with the Grenville and Dannemora 

 rocks. 



Other syenite areas. So far as the Adirondack region has been 

 studied, these syenites seem to be more abundant and important 

 rocks in Franklin county than elsewhere, though it is possible 



^17th An. Rep't State Geol. p.474-81. 



