PENNSYLVANIA. 77 
sometimes in a lens of chlorite; some large plates of muscovite and of chlorite inter- 
leaved with muscovite, up to 0.06 mm., and rarely a zircon fragment, 0.03 mm. 
The constituents of this slate, arranged in descending order of abundance, appear 
to be muscovite (sericite), carbonate, quartz, kaolin, pyrite, chlorite, rutile, mag- 
netite, and carbonaceous matter or graphite. 
The final results of Professor Merriman's physical and chemical tests of "Old Ban- 
gor" slate are given here for convenience of reference: Strength (modulus of rupture I, 
9,810 pounds per square inch; toughness (ultimate deflection on supports 22 inches 
apart), 0.312 inch; density (specific gravity), 2.780; softness (amount in grains 
abraded by 50 turns of a small grindstone) , 128; porosity (per cent of water absorbed 
in twenty-four hours), 0.145; corrodibility (per cent of weight lost in sixty-three 
hours in acid solution composed of 98 per cent H 2 0, 1 per cent HC1, 1 per cent S( >.., i. 
0.446. Per cent of lime, 4.38; computed carbonate of lime, 7.82 per cent; computed 
carbonate of magnesia, 5.65 per cent/' 
The product from the large beds is used for roofing, but that from the ribboned 
beds goes into mill stock. 
Quarries* of the North Bangor Slate Company. — The large quarry is about 200 feet 
square and 350 feet deep. The folded beds strike about N. 60° E. and the cleavage 
dips south westward, at an angle of 15°. The total thickness of good slate here, 
measured across the cleavage, is 300 feet. In the smaller quarry the thickest bed 
measures 9 feet, and is reserved for blackboards. 
In a quarry adjacent to the first of these two quarries, operated by Auld & Conger, 
a completely overturned syncline, several hundred feet from northwest to southeast, 
is exposed on the east-northeast wall, with an almost horizontal cleavage. 
The slate from these quarries is very dark gray, and to the unaided eye has a fine 
texture and a very smooth cleavage surface, with but slight luster. It is somewhat 
carbonaceous or graphitic, and contains some magnetite. The sawn edge shows 
pyrite. It effervesces somewhat freely with cold dilute hydrochloric acid; is sonorous, 
and has an argillaceous odor. 
Specimens from the North Bangor Slate Company's quarry show, under the micro- 
scope, a matrix of muscovite (sericite) with a somewhat brilliant aggregate polariza- 
tion and a general uniformity in size of particles. The aggregate polarization is 
partly obscured by the very abundant carbonate. Quartz fragments are not very 
abundant and measure up to 0.04 mm. There are some chlorite scales up to 0.09 mm., 
and about three hundred and sixty spherules of pyrite, measuring-up to 0.01 mm. to 
each square millimeter. Also carbonaceous matter or graphite and very abundant 
rutile needles. 
The constituents, arranged in descending order of abundance, appear to be mus- 
covite (sericite), carbonate, quartz, kaolin, pyrite, chlorite, magnetite, rutile, carbona- 
ceous matter or graphite. In a black-ribboned piece from the same quarries the 
half-inch ribbon shows much carbonaceous matter and many spherules of pyrite. 
The quartz particles and the plates of carbonate are larger in the ribbon than in the 
adjacent slate. The product of this company's quarries is used for blackboards, bil- 
liard tables, fireboards, stationary tubs, well covers, tiles, lathe work, etc. 
East Bangor.— The large quarry of the East Bangor Consolidated Slate Company 
measures 350 feet along the strike and 700 feet across by 130 feet in depth. The beds 
dip 5° NNE. and the cleavage 15° to 20° SSW. The main joints strike north and 
south and undulate in a general vertical direction. The grain strikes N. 50°-00° W. 
Ribbons are frequent, The slate is very dark-bluish gray, and to the unaided eye has 
a fine texture and a somewhat fine but almost lusterless cleavage surface. It is both 
carbonaceous, or graphitic, and magnetitic. The sawn edge shows a little pyrite. It 
a Trans. Am. Soc. Civ. Eng., vol. 27, 1892 (3), p. 342-347. 
