﻿36 NEW YORK STATE MUSEUM 



and Rossie, just east of our map, has been noted here, but with 

 that exception there is a strong resemblance in the material. 



Igneous rocks. Gneissic granites (Laurentian) . There are two 

 extensive (bathylithic) masses of granite gneiss in the district, 

 both of which are only in part within the mapped area. The 

 western end of what we have called the " Antwerp bathylith " 

 is exposed on the Theresa quadrangle, disappearing westward 

 under a Paleozoic cover. The Alexandria bathylith, on the main- 

 land and islands of the Alexandria quadrangle, seems of smaller 

 size but also disappears under a Paleozoic cover, both eastward 

 and westward, and passes across into Canada as well. There are 

 in addition numerous smaller masses. It is highly probable 

 that all are connected underground, and represent the upper 

 portions of a great,- underground mass of granite, underlying all 

 of the Grenville of the district, except where cut away by the 

 later intrusions. 



That this granite came to its present resting place after the 

 Grenville was deposited was pointed out by Smyth 10 years ago, 

 and is shown clearly in a host of exposures.. Dikes without 

 number run out from the granite masses into the Grenville rocks, 

 the granite is everywhere full of included fragments of the Gren- 

 ville, and along the contacts between the two sets of rocks, the 

 Grenville rocks have plainly been modified by the contact action 

 of the intrusive. 



The general rock is a quite acid, red granite, composed chiefly 

 of feldspars (microperthite, microcline and oligoclase) and 

 quartz, with small amounts of mica (both biotite and muscovite) 

 and magnetite, and with zircon, titanite and apatite as acces- 

 sories. Such rock does not appear especially gneissoid, though 

 usually of rather fine and even grain, but in thin section it 

 invariably shows much crushing, and a considerable amount of 

 recrystallization. The rock is everywhere cut by its own aplite, 

 pegmatite and quartz dikes, some of which are much coarser 

 grained, as usual. Many of the granite dikes which penetrate 

 the Grenville, especially the limestones, are coarser grained, and 

 less mashed than the general rock. 



In a minor way the rock of the bathyliths is quite variable, 

 and that in two main ways, one apparently representing original 

 variations in the rock, and one owing to relative abundance of 

 inclusions and the effect of the granite on them. The rock varies 

 from one which is almost wholly constituted of feldspars and 

 quartz, to one which contains several per cent of mica, which 



