30 NEW YORK STATE MUSEUM 



tance of lo or 20 feet. Closer inspection shows that the light and 

 dark bands, usually alternating, with thicknesses of from less than 

 a millimeter to several centimeters are really not very sharply sep- 

 arated, but are connected by tiny interlocking crystals. The main 

 bulk of the rock is fine grained, but scattered through it there are 

 many light-red garnets from less than a millimeter to 5 millimeters 

 in diameter, these garnets constituting 10 to 15 per cent of the rock. 

 The nearly white bands are aplitic grano-syenite, and the light to 

 dark-gray bands represent old dark gneiss (presumably Grenville) 

 more or less highly injected and possibly somewhat digested by 

 aplitic granite. The dark bands are highly biotitic, and most of the 

 rounded garnets are irregularly scattered through them. The bands 

 of white aplite contain very few garnets. A thin section cut across 

 the banded structure of the typical rock shows the following min- 

 erals by volume percentages: plagioclase (oligoclase to andesine), 

 40; quartz, 38; garnet, lo^^ ; biotite, 10; magnetite, 1% ; and a little 

 zircon and apatite. Within the bands of the section the minerals 

 are rather irregularly arranged, even the biotite laths. 



Another outcrop showing rock much like that last described 

 occurs by the river road 2 miles southwest of Conklingville. It is 

 a ledge 150 feet wide across the strike. The rock is very distinctly 

 straight banded, some of the white aplitic bands being i to 2 inches 

 wide with scattering garnets. The dark bands of highly injected 

 old gneiss are rich in biotite and garnet. Both the white and dark 

 rocks are highly foliated with the dark facies predominant. A thin 

 section of this rock cut across the bands shows the following volume 

 percentages of minerals : quartz, 30 ; microperthite, 30 ; plagioclase 

 (oligoclase to andesine), 18; microcline, 12; biotite, 5; garnet, 3; 

 magnetite, i ; muscovite, y^ ; and a little hematite, apatite and zir- 

 con. The section is very highly foliated in thin bands, with notable 

 concentration of certain minerals in definite bands. One difference 

 from the previously described mixed rock is that this ledge con- 

 tains a good many bands of greenish gray rather richly biotitic rock 

 without garnets. These bands, usually several inches wide and par- 

 allel to the foliation, are decidedly syenitic or dioritic in appear- 

 ance, and they are notably less foliated than the associated light and 

 dark garnetiferous rocks. An old dark gneiss (presumably Gren- 

 ville) has in this case also been more or less cut and injected by an 

 aplitic facies of the syenite-granite magma. Very similar mixed 

 rock occurs in good exposures along the road across the area north 

 of Hunt lake, but there the igneous bands predominate. Good 

 exposures of somewhat similar rock also occur west of south of 



