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these more advanced stages are usually found in the case of 

 inclusions away from the near vicinity of the border. 



We have not, up to the present time, definitely classed any 

 of the granites of northern New York as of Laurentian age. Just 

 across the border in Canada however, where the rocks are identi- 

 cal, this term is definitely applied to the granite gneiss of the 

 bathyliths which invaded the Grenville series from beneath, 

 broke it up into disconnected belts and patches and destroyed 

 all trace of its floor. The absolute identity of the rocks and their 

 relations, leads us to apply the name here to the granite gneiss 

 bodies with much confidence in the wisdom and propriety of the 

 correlation. Whether these Laurentian granites are recognizable, 

 however, over any considerable part of the Adirondack 

 region, in distinction from granites of later date, is a much less 

 certain matter, though we believe it to be the case. It is thought 

 for example that what we have called the Saranac gneiss in 

 Clinton county, and the Long Lake gneiss of that quadrangle, 

 are in all probability of Laurentian age. 



Theresa syenite. This comparatively small intrusive mass lies 

 to the southward of Theresa, in a valley floored by Precambric 

 rocks, but walled in by Potsdam on all sides It is somewhat 

 less than 2 miles in length and with a breadth of less than half a 

 mile, so far as the exposures go; at the south it may have greater 

 breadth underneath the Potsdam. 



The general rock is of medium coarseness and granitic texture, 

 though always with evidence of mashing and granulation, and 

 of gray to greenish color. Most of it is chiefly made up of feld- 

 spars. It resembles in high degree the common greenish, augite 

 syenite of the Adirondack region, is unhesitatingly classed with 

 that, and is the only representative of that rock type within the 

 mapped area. Like it, this rock is quite variable, becoming red 

 and granitic looking on the one hand, and more basic with 

 increase of black minerals on the other. Near the border some 

 varieties become feebly porphyritic. 



Microperthitic feldspar is always the chief constituent of the 

 rock. Some oligoclase is always present. Quartz varies from 

 some 15$ in the more granitic, red varieties, down to complete 

 absence. Augite is the most prominent black mineral in the 

 ordinary rock, with biotite usually and hornblende sometimes 

 sparingly present; magnetite, apatite, titanite and zircon are the 

 chief accessories, the apatite usually quite prominent, another 

 feature which the rock has in common with the general Adiron- 



