74 
SLATE DEPOSITS AND INDUSTRY OE UNITED STATES. 
Bright-greenish slate. — The reddish slate is usually interbedded and exceptionally 
passes along the strike into a light bluish-green slate, brighter in color than the 
"unfading green" Cambrian slates of Vermont. Its color is peculiarly bright by 
lamplight; its texture and surface are similar to those of the "red," and the surface 
is also sometimes speckled with minute lenses. It is magnetitic, effervesces very 
slightly with cold dilute hydrochloric acid, is sonorous and is said to be unfading. 
Under the microscope shows a matrix of muscovite (sericite) with a more brilliant 
aggregate polarization than that of the red slates, which may be due to the absence 
of the hematite, but the coarseness of the particles does not indicate a superior fissil- 
ity. There are quartz grains up to 0.084 by 0.056 mm., chlorite scales up to 0.043 
mm., some carbonate rhombs from 0.002 to 0.056 mm., and lenses measuring up to 
0.385 by 0. 128 mm. , that consist either of rhodoch rosite or chalcedonic quartz inclosing 
very minute carbonate rhombs and chlorite scales. Sections parallel to the cleavage 
show these lenses with a more roundish outline. There are also particles of pyrite, 
tourmaline prisms, rutile needles, and grains of zircon. 
The chief constituents of this slate, arranged in descending order of abundance, 
appear to be muscovite (sericite), quartz, chlorite, carbonate, magnetite, rutile. 
Its color is due to the abundance of chlorite. 
Bright-greenish roofing slate. — The following analysis (specimen 0=D. XIV, '95, 
397c), by Dr. W. F. Hillebrand, is of a bright-greenish speckled slate from the 
National Red Slate Company's quarry, 1 mile north of Raceville, in Granville, Wash- 
ington County, N. Y. 
Analysis of bright-greenish slate from New York. 
Si0 2 (silica) 67. 89 
Ti0 2 (titanium dioxide) 49 
A1 2 3 (alumina) 11. 03 
Fe 2 3 (ferric oxide) 1. 47 
FeO (ferrous oxide) 3. 81 
MnO ( manganous oxide ) 16 
NiO (nickelous oxide) Trace? 
CoO (cobaltous oxide) Trace? 
CaO (lime) 1. 43 
BaO (baryta) 04 
MgO (magnesia) 4. 57 
K 2 (potassa) 2. 82 
Na 2 (soda) 
Li 2 0(lithia) 
H 2 (water below 110° C. ) 
H 2 (water above 110° C.) 
P 2 5 (phosphoric oxide) 
.77 
Trace. 
.36 
3.21 
.10 
C0 2 (carbon dioxide) 1. 89 
FeS 2 (pyrite) 04 
S0 3 (sulphuric oxide) Trace. 
C ( carbon ) None. 
Total 100.08 
S (sulphur, total) 022 
Specific gravity =2. 7171. 
The relatively high percentage of magnesia is attributed to the abundance of both 
dolomite and chlorite. 
The results of Professor Merriman's recent tests of the bright-greenish slates 
quarried by the Mathews Consolidated Slate Company are given on page 123. 
Black slate. — Black roofing slate of Ordovician age was quarried many years ago, in 
a small way, 3 miles south of Hoosick Fails, near Hoosick, and also, at a later time, 
2 miles south of Stephentown, near Lebanon Springs, in Rensselaer County, N. Y., 
but did not prove to be of economic importance at either locality. a 
The principal features of New York slates as brought out in the above descriptions 
will be found in tabular form opposite page 124. 
a PI. CI and fig. 26, Thirteenth Ann. Rept. U. S. Geol. Survey, show the structure at the Lebanon 
Springs quarry. 
