MAINE. 63 
west and thus parallel to the grain. The northeast half of the quarry is much 
broken up by diagonal jointing and faulting, but in the southwest half conditions arc 
more normal, although veining is there more frequent. The difference between fin- 
jointing of the quartzite and the slate results from the difference in their rigidity. 
Their behavior under the same stress must needs have been very dissimilar. The 
quartz veins traversing the slate sometimes contain biotite, chlorite, and a little cal- 
cite. The surface of the formation is glaciated and covered with from 5 to 10 feet of 
glacial clay and pebbles. 
The slate itself is very dark gray, but at the glaciated surface some of the beds 
have in bright sunlight a very slightly purplish hue. The fifth bed from the north 
edge is slightly brownish. To the unaided eye both texture and surface are fine, but 
the latter is almost lusterless. It is slightly carbonaceous or graphitic, and has very 
little magnetite. The sawn edge shows a little pyrite. No effervescence in cold 
dilute hydrochloric acid. It is very sonorous. 
Under the microscope this slate shows a matrix of muscovite (sericite) with a 
brilliant aggregate polarization, but there is considerable irregularity in the size of 
the particles. Quartz fragments measure up to 0.017 by 0.008 mm. Occasional 
quartz lenses measure 0.094 by 0.047 mm. There are to each square millimeter from 
30 to 40 scales of chlorite (interleaved with muscovite, rarely with biotite) measuring 
up to 0.047 by 0.03 mm. and lying transverse to the cleavage; also about ten scales 
of biotite to each square millimeter measuring up to 0.086 by 0.02 mm., lying both 
across and with the cleavage, and longish crystals and lenses of pyrite with their 
long axes parallel to the grain, numbering about fifty to the square millimeter and 
measuring up to 0.075 by 0.028 mm. These crystals are mostly distorted cubes, but 
mingled with them are probably some distorted octahedra of magnetite. Scattered 
throughout is dark-gray carbonaceous or graphitic matter in extremely minute par- 
ticles, to which and to the biotite the slate owes its blae 7 .ness. Finally, a few deli- 
cate rutile prisms, 0.001 mm. long, some specks of hematite, and a few tourmaline 
prisms up to 0.036 by 0.004 mm. No carbonate detected. 
The constituents of this slate, arranged in the order of their decreasing abundance, 
appear to be muscovite (sericite), quartz, chlorite, biotite, pyrite, carbonaceous or 
graphitic matter, magnetite, rutile, and apatite. 
The only available chemical analysis of this slate is that by L. M. Norton, « which 
shows 56.42 per cent of Si0 2 , 24.14 per cent of A1 2 8 , and 0.52 per cent of CaO. This 
small percentage of lime, taken in connection with the occurrence of a little calcite 
in the quartz veins, points to the presence of an insignificant amount of carbonate, 
which the microscope fails to detect. But a little of this lime belongs to the apatite. 
The specific gravity is given by Bailey as 2.851. Tests of the crushing weight and 
strength made at the Massachusetts Institute of Technology show that a cubic inch 
of this slate yields to the pressure of 30,425 pounds when applied at right angles to 
the cleavage, and that a slab, 12 by 6 by 1 inches, supported on knife edges 10 inches 
apart, breaks under a stress of from 3,950 to 4,000 pounds applied at the center with 
a steel rod, five-sixteenths inch in diameter, placed b, tween the slate and the pres- 
sure block. This gives a modulus of rupture of 9,937 pounds per square inch. 
This slate is split to seven thirty-seconds of an inch for roofing. It is also used for 
electric purposes, register borders, blackboards, refrigerator shelves, etc. 
At the quarry of the Maine Slate Company of Monson, 3| miles west-southwest 
of the village, opened in 1903, there are about 30 feet of slate and interbedded 
Iquartzite exposed. The thickest bed of slate measures about 8 feet. In 1904, the 
quarry measured about 100 feet along the strike, 30 feet across it, and 40 feet in 
(depth. The bedding strikes N. 55°-60° E., and dips about 80° SSE., but at the sur- 
face curves over steeply north-northwest. The cleavage strikes about the same, but 
I a See Bailey, W. S., Bull. U. S. Geol. Survey No. 150, 1898, p. 313, aud Twentieth Ann. B^pt., Pt. VI 
i(Cont.), 1899, p. 394. 
