20 NEW YORK STATE MUSEUM 



feldspar and a large proportion of quartz and the dark colored 

 minerals. Thus a specimen from along the railroad 2^ miles 

 north of Lyons Falls contains 75^ of microperthite; 2ofo of 

 quartz; 5^ of magnetite, biotite and hornblende, together with 

 a little zircon. Another from % of a mile southwest of Goulds 

 Mill contains 65^, in about equal amounts, of microcline, micro- 

 perthite and plagioclase (oligoclase to labradorite) ; 2^fo of 

 quartz; and lofo of biotite and magnetite. North of Lyons Falls, 

 along the railroad, similar rocks often carry 30 to 40^^ of quartz 

 with sometimes a little anorthoclase and they greatly resemble 

 the granitic syenite. 



2 Grenville facies. Small exposures often show very pure 

 Grenville as for example at the river dam }^ mile north of Port 

 Leyden. A thin section from here shows 80^ quartz; lofo silli- 

 manite; 8^ magnetite and 2fo biotite, together with a little zircon. 

 Again, a typical pyroxene, quartz gneiss is associated with syen- 

 itic rocks i^ miles above the mouth of Miller brook. A Grenville 

 facies carrying garnets occurs in the vicinity of the paper mill at 

 Lyons Falls. 



3 Garnetiferous gneisses with a general igneous appearance are 

 very common. Such a rock 2 miles east of Port Leyden shows 65,^ 

 of microcline and microperthite; 20;^ of quartz; 5^ of hornblende 

 and biotite and lo'/c of augite, magnetite, garnet and zircon. 

 A similar t3^pe much richer in garnet and almost free from dark 

 minerals occurs in the river bed at Port Leyden. Another type 

 from 2^ miles east-southeast of Greig shows 65;^ of plagioclase 

 (oligoclase to labradorite) ; 30^ of quartz and 5^ of biotite, gar- 

 net, magnetite and zircon. The origin of these gneisses is doubt- 

 ful but they may have been formed by a thorough mixing of 

 Grenville masses with the molten syenite. The garnets in these 

 rocks are frequently an inch or more across. 



4 A very gneissoid, rather dark rock, which is fairly common, 

 is rich in plagioclase, quartz and biotite. An example from ^ 

 mile south of Lyons Falls contains 45^ of plagioclase (oligoclase 

 to andesin) ; 40^ of quartz ; 10^ of biotite ; 2^ of hornblende and 

 3^ of magnetite, zircon and pyrite. 



5 A very gneissoid, dark rock from i^ miles east of Port 

 Leyden contains 50;^ of microcline and plagioclase (oligoclase 

 to labradorite) ; 20^ of quartz and lofo each of green augite, biotite, 

 magnetite and a very little garnet. 



6 A type of dark, quartzless, gabbroic rock such as that at 

 Lyons Falls dam contains 55^ of plagioclase (oligoclase to labrador- 



