GEOLOGY OF THE PARADOX LAKE QUADRANGLE 495 



The quartz usually constitutes about 40,^ of the rock; feldspar 

 over 50^; the remaining dark silicates being thus small in quantity. 

 Unfortunately the rock was invariably too greatly weathered for an 

 analysis to be accurate, but it is confidently believed that if such an 

 analysis could be made the silica content would be high enough to 

 place the rock without doubt among the sediments. 



The biotite schist which forms bands in this gneiss and in the 

 limestone is found to contain large quantities of quartz. Quartz 

 forms from 20^ to 30,^ of the rock and biotite is present in 

 about the same amount. The remainder of the rock is made up 

 of feldspars (microcline, albite, labradorite and oligoclase all being 

 found, usually one variety predominating and one other being less 

 in amount), garnet, zircon, apatite, and magnetite, in varying 

 proportions. 



The probability concerning this gneiss is that it represents the 

 base of the Grenville series, which has suffered from the meta- 

 morphism common to the region as a whole, and which has experi- 

 enced in addition an excessive amount of recrystallization and 

 squeezing from being nearest to the intrusives. 



Sillimanite gneiss. Thin sections of the rock at Graphite show 

 large garnets embedded in a mass of fibrous sillimanite. The silli- 

 manite crystals show a roughly parallel arrangement. A little 

 quartz is present and accessory zircon, pyrite and graphite. The 

 foot and hanging wall are similar, except that the foot wall contains 

 microperthite in addition tO' the minerals found in the hanging wall. 



The sillimanite gneiss from Bear Pond mountain contains similar 

 shreds of sillimanite. Biotite is present in large quantities, the 

 biotite being younger than the sillimanite. In the prevailing type 

 shreds of biotite and of sillimanite are arranged in parallel groups, 

 the terminal faces of both being lacking. Occasionally a sillimanite 

 crystal is found cutting across the biotite at right angles to its long 

 axis, and in such cases it is the sillimanite that has the perfect boun- 

 dary. Accessory pyrite and rutile are sometimes present. 



Petrography of the igneous rocks 



Of the four types of igneous crystalline rocks found on the Para- 

 dox Lake quadrangle — granite, syenite, anorthosite, and gabbro — 



