78 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
effervesces slightly with cold dilute hydrochloric acid; is sonorous, and has a scarcely 
perceptible argillaceous odor. 
Under the microscope a specimen taken between "ribbons" shows a matrix of 
muscovite (sericite) with a brilliant aggregate polarization, somewhat obscured by 
carbonate, a texture a little finer than that of "Old Bangor" slate, but carbonate as 
abundant as in that. Not very much quartz in grains measuring up to 0.04 by 0.02 
mm. ; about seventeen scales of chlorite, with interleaved muscovite, to each square 
millimeter, measuring up to 0.07 by 0.03 mm., exceptionally 0.08 by 0.04 mm. ; about 
six hundred spherules of pyrite per square millimeter, measuring up to 0.008 nun.; 
rutile needles very abundant; carbonaceous or graphitic matter in fine particles. 
The chief constituents of this slate, arranged in descending order of abundance, 
appear to be muscovite, carbonate, quartz, pyrite, chlorite, kaolin, rutile, carbonaceous 
matter or graphite, magnetite. 
The product of this quarry is used both for roofing and for mill stock, but not for 
blackboards, as the 9-foot bed is crossed by ribbons. The roofing slates are said to 
show comparatively little discoloration after thirty years' exposure. 
II< iiiihuclt.— The Heimbach quarry about 1£ miles northeast of Slatington, but in 
Northampton County, is now operated by Jay S. Mover & Co. There is a thick bed 
here known as the " Heimbach big bed," which is very dark gray and less bluish 
than " Old Bangor." To the unaided eye it has a tme texture and a somewhat fine 
but almost lusterless cleavage surface. It contains an exceedingly small amount of 
magnetite; effervesces with cold dilute hydrochloric acid, and is sonorous. 
Under the microscope it shows a matrix of muscovite (sericite), with but faint aggre- 
gate polarization owing to the abundance of carbonate, which much exceeds that in 
the "Old Bangor" slate. The cleavage is considerably finer and there is greater 
regularity in the size of particles than in that slate. There are a few chlorite scales 
up to 0.06 by 0.04. Very little quartz is seen, in grains reaching only 0.036 mm. 
Pyrite spherules measure up to 0.012 mm. and number about 116 per square milli- 
meter. Rutile needles are very abundant. The usual carbonaceous matter is seen. 
The constituents of the "Heimbach big bed," arranged in descending order of 
abundance, appear to be muscovite (sericite), carbonate, quartz, pyrite, chlorite, 
rutile, carbonaceous matter, magnetite, but the carbonate is larger in amount than in 
some slates in which its relative position is the same. 
There is also in the same quarry a 6-foot bed, which is quite black, more so than 
any of the Northampton or Lehigh County slates. It has, to the unaided eye, a 
somew r hat fine texture and cleavage surface with a slight luster. It shows pyrite 
on the sawn edge, is quite carbonaceous or graphitic, very slighly magnetitic, effer- 
vesces in cold dilute hydrochloric acid, is sonorous, and has a slight argillaceous odor. 
Under the microscope the "Heimbach black bed" shows a fine matrix of musco- 
vite (sericite), with but faint aggregate polarization owing in part to the very large 
amount of carbonate and carbonaceous matter. The number of quartz fragments is 
relatively small and they measure up to 0.028 mm. There are chlorite scales up to 
0.06 mm. Spherules of pyrite measure up to 0.008 mm., exceptionally 0.017 mm. 
and number about 135 per square millimeter. Rutile needles abound. Rarely a 
scale of hematite is seen. 
The chief constituents of this slate, arranged in descending order of abundance, 
appear to be muscovite (sericite), carbonate, quartz, carbonaceous matter and graph- 
ite(?), pyrite, chlorite, rutile, magnetite, the percentage of carbonate being, however, 
large. 
The principal difference between the Heimbach and "Old Bangor" slate is in the 
larger amount of carbonate, lesser amount of pyrite, and the finer structure of the 
former, judging from the microscopic evidence. 
Pen Argyl. — The Albion quarry at Pen Argyl is regarded as being near the bottom 
of the "soft vein" belt. It measures 650 feet along the strike, 600 feet across it, 
