42 NEW YORK STATE MUSEUM 



15 per cent albite, 44 per cent quartz, i per cent magnetite, and a 

 little zircon. The rock is moderately gneissoid and variable in 

 grain from medium to coarse. Possibly it is an acidic off-shoot 

 from the neighboring syenite. 



On the southern side of the top of Catamount mountain, a num- 

 ber of small nonfoliated aplite dikes lie parallel to the foliation of 

 the coarse granite. Whether these are younger or older than the 

 neighboring gabbro-dlorite dikes was not definitely determined, but 

 the aplites are probably the older. 



At number 17, i mile west of East Kilns, a fine aplite dike 3 

 feet wide cuts a big ledge of coarse granite. A thin section shows 

 the following mineral percentages : Microperthite, 58 ; microcline, 

 I ; albite, 5 ; quartz, 35 ; biotite, i ; and very little garnet, apatite 

 and zircon. The rock is not gneissoid. The fact that the contact 

 against the granite is not very sharp strongly suggests that the 

 aplite was intruded while the granite was still fairly hot. 



At dike locality no. 18 several small aplite dikes cut granite. 



Granite-pegmatite dikes. Nos. 5, 6, 7, 8, 10, 13, 14 and 16, indi- 

 cated on the geologic map, are pegmatite dikes of the usual sort. 

 They are nonfoliated and cut the Grenville, anorthosite, and syenite- 

 granite series. No. 8 lies in contact with a diabase dike, and these 

 two clearly cut syenite. No. 16 is a pegmatite dike 3 feet wide 

 very sharply cutting across the foliation of one of the gabbro- 

 diorite dikes below described. Within the Lake Placid quadrangle 

 no pegmatite was observed cutting the gabbro stocks (below 

 described), but in various portions of the Adirondacks dikes of 

 such have been found to be intrusive into the gabbro. It is quite 

 possible that these pegmatite dikes are not all of the same age, but 

 all are. doubtless younger than the syenite-granite series, most of 

 them probably representing a late stage in the intrusion and cooling 

 of the syenite-granite magma. 



Syenite-pegmatite dikes. A much more unusual type of pegma- 

 tite dike was noted at several localities, namely, near Franklin Falls 

 (d'ke no. 19) ; i]/^ miles south of Wilmington (dike no. 20) ; and 

 I mile southwest of Haselton (dike no. 21). These are very coarse- 

 grained rocks consisting chiefly of irregular masses of microperthite 

 and black hornblende (or pyroxene) up to several inches across. 

 No quartz occurs. Dike no. 19 is 2 feet wide, cuts Whiteface anor- 

 thosite, and contains masses of magnetite i or 2 inches across. The 

 contact against the country rock is not sharp. At no. 20 a number 

 of pegmatite dikes from i to several feet wide cut ]\Iarcy anor- 

 thosite usually without sharp contacts. 



