THE NONMETALLIC MINERALS. 293 



area south of the Ottawa River the Lauren tian is concealed by the mantle of Cambro- 

 Silurian rocks belonging to the Ottawa River basin, but it may be said that the geo- 

 logic conditions and the stratigraphic sequence in the area south of the Ottawa and 

 in the rear of Kingston are the same as those found in the mineral-bearing belts 

 north of the Ottawa, and that the most favorable conditions under which the deposits 

 of mica and apatite may be looked for w r here traces of igneous agency are visible in 

 the presence of dikes of pyroxene and quartz feldspar, though it should be stated 

 that the mere occurrence of these in the gneiss does not warrant the presence of 

 either of these minerals. 



The India mica mines occur in coarse intrusive pegmatitic-granite 

 dikes, cutting what is known as the "newer gneiss" of Singrauli. At 

 Inikurti the crystals (of mica) are as much as 10 feet in diameter. 

 Sheets 4 or 5 feet across have been obtained free from adventitious 

 inclusions which would spoil their commercial value. 1 



Black mica (biotite, lepidomelane, etc.,) is a much more common 

 and widely distributed variety than the white, but unlike the latter is 

 found not so much in veins as an original constituent disseminated in 

 small flakes throughout the mass of eruptive and metamorphosed 

 sedimentary rocks. The small sizes of the sheets, their color, and 

 lack of transparency render the material as a rule of little value. In 

 Renfrew County, Canada, the mineral occurs in large cleavable masses, 

 which yield beautiful smoky-black and greenish sheets sufficiently 

 elastic for industrial purposes (Specimens Nos. 62735, 62709, U.S.N.M.). 



Lepidolite. This variety of mica is much more rare than any of 

 the others described. While in a few instances it has been reported as 

 accompanying rnuscovite in certain granites, as those of Elba and 

 Schaistausk, its common form of occurrence is in the coarse pegmatitic 

 veins already described, where it is associated with muscovite, tourma- 

 lines, and other minerals of similar habit. As a rule it is readily distin- 

 guished from other micas by its beautiful peach-blossom red color, 

 though sometimes colorless and to be distinguished only by the lithia 

 reaction. 2 The folia are thicker than those of muscovite and of small 

 size, the usual form being that of a scaly granular aggregate. At Au- 

 burn, Maine, it is found both in this form (Specimen No. 61079, 

 U.S.N.M.) and forming a border a half inch, more or less, in width 

 about the muscovite folia (Specimen No. 13810, U.S.N.M.). The 

 more noted localities in the United States are Auburn, Androscoggin 

 County; Hebron, Paris, Rumford (Specimen No. 63003, U.S.N.M.), 

 and Norway, Oxford County, Maine, where it is associated with beau- 

 tiful red and green tourmalines and other interesting minerals; Ches- 

 terfield, Massachusetts; Iladdam, Connecticut (Specimen No. 53540, 

 U.S.N.M.), and near San Diego, California (Specimen No. 62593, 

 U.S.N.M.). The most noted foreign locality is Zinnwald, Saxony, 



Geology of India, 2d ed., 1893, p. 34. 



2 The pulverized mineral when moistened with hydrochloric acid and held on a 

 wire in the flame of a lamp imparts to the flame a brilliant lithia red color. 



