THE NONMETALLIC MINERALS. 287 



As seen by the writer, the veins at the latter place cut sharply across the fibrolitic 

 schist, and though the vein materials adhere closely to the wall rock on either side, 

 without either selvage or slickensides, still the line of demarcation is perfectly sharp. 

 There seems no room for doubt but that the vein material was derived by injection 

 from below, though from their extremely irregular and universally coarsely crystal- 

 line condition we must infer that the condition of the injected magma was more in 

 the nature of solution than fusion, as the word is ordinarily used, and also that the 

 rate of cooling and consequent crystallization was very slow. The feldspars not infre- 

 quently occur in huge crystalline masses several feet in diameter, though sometimes 

 more finely intercrystallized with quartz in the form known as pegmatite. [Specimen 

 No. 62519, U.S.N.M.] The mica is by no means disseminated uniformly throughout 

 the vein, but on the contrary is very sporadic, and the process of mining consists merely 

 in following up the mineral wherever indications as shown in the face of the quarry 

 are sufficiently promising. Most of the mines are in the form of open cuts and trenches, 

 though in a few instances underground cuts have been made for a distance of a hun- 

 dred feet or more. The mica blocks as removed are of a beautifully smoky-brown 

 color, and often show a distinct zonal structure, indicating several periods of growth. 

 The associated feldspar is not in all cases orthoclase, but, as at the Alexandria mines, 

 sometimes a faintly greenish triclinic variety. 



Samples of the New Hampshire micas, with the accompanying 

 gangue and wall rocks, are shown in Specimens Nos. 02515 to (32519 

 and 63028 to 63030, U.S.N.M. 



In Connecticut some mica (muscovite) has been obtained in connec- 

 tion with the work of mining feldspar and quart/ in and about the 

 towns of Haddam, Glastonbury, and Middletown, but the business has 

 never assumed any importance. Mica mines have also been worked 

 in Montgomery County, Maryland. South of the glacial limit mica 

 mining has proven more successful from the reason that the gangue 

 minerals (feldspar and quartz) were in a state of less compact aggre- 

 gation, due to weathering, the feldspar being often reduced to the 

 state of kaolin, and hence readily removed by pick and shovel. The 

 following account of the deposits of North Carolina is given by Prof. 

 W. C. Kerr: 1 



I have stated elsewhere, several years ago, that these veins were wrought on a 

 large scale and for many ages by some ancient peoples, most probably the so-called 

 Mound Builders; although they built no mounds here, and have left no signs of any 

 permanent habitation. They opened and worked a great many veins down to or 

 near water-level; that is, as far as the action of atmospheric chemistry had softened 

 the rock so that it was workable without metal tools, of the use of which no signs are 

 apparent. Many of the largest and most profitable of the mines of the present day are 

 simply the ancient Mound Builders' mines reopened and pushed into the hard unde- 

 com posed granite by powder and steel. Blocks of mica have often been found half 

 imbedded in the face of the vein, with the tool-marks about it, showing the exact 

 limit of the efficiency of those prehistoric mechanical appliances. As to the geolog- 

 ical relations of these veins, they are found in the gneisses and schists of the 

 Archaean horizons. * * * These rocks are of very extensive occurrence in 

 North Carolina, constituting in faot the great body of the rocks throughout the 

 whole length of the State, some 400 miles east and west, being partially covered 



1 Transactions of the American Institute of Mining Engineers, VIII, 1880, p. 457. 



