NEW YORK. 
71 
Granville and Jamesville. Overlying the Lower Cambrian, in isolated lenticular 
synelinal areas or in long, ramifying masses of complex structure, art; Ordovician 
(Hudson) grits and black, red, and green shales; and these red and green shales 
pass here and there into roofing slates. a 
While the Lower Cambrian greenish and purplish slates are at present quarried 
almost exclusively on the Vermont side of the boundary, the red and green slates 
attain their best development on the New York side, particularly in the towns of 
Granville, Whitehall, and Hampton. The structural relations of the two slate- 
bearing formations on the New York side are shown in sections I, II, VII of PI. 
XXII, and are explained in detail on page 100. 
As to mode of occurrence, these red and green slates seem at several points to 
replace the Hudson grit along the strike. Certainly these slates occur in as close 
proximity to the Cambrian slates as does the grit. Black graptolite shale sometimes 
crops out very near to and probably underlies the red slate. Beds of red and green 
slate alternate vertically, and replace one another along the strike, and also pass 
into shales of the same colors. The thickness exposed at the quarries reaches 50 
and 75 feet, mostly red, with about 25 feet of green overlying, but, subtracting that 
which is too hard or too soft or badly veined, there are sometimes but 10 feet, rarely 
more than 25 feet, of good red slate exposed at any one quarry, although it some- 
times reaches 42 feet. Owing to the character of the folds and their pitch, as well 
as the merging of the colors along the strike, it is not easy to ascertain the total 
thickness of the red and green. A few feet or inches of dark red or purple some- 
times occur in the red. Beds of greenish quartzite, sometimes calcareous, and bor- 
dered by a purple slate, the whole "ribbon" measuring an inch or two in thick- 
ness, are not uncommon (see PL II, A). Also beds one-half inch thick of rhodo- 
chrosite (manganese carbonate) with crystalline calcite. 
An analysis of this (Specimen D. XIV, '95, 201d), made by Mr. George Steiger, 
yielded the following: 
Analysis of rliodochrosite bed. 
A1 2 3 
Fe 2 3 
FeO 
MnO 
NiO and CoO 
CaO 
0.68 
.14 
1.13 
32.22 
.10 
3.81 
MgO 
co 2 
Insoluble matter, including all sil- 
ica from dissolve* I silicates 
Total 
2.61 
25.06 
32.75 
98.50 
Under the microscope thin sections of this bed show, with polarized light, a fine- 
grained bluish-brown matrix identical in color and texture with that of the small 
lenses in the red slate and with some of the lenses in the green slate; also large areas 
of calcite and some quartz. 
There are also quartz veins in both red and green, sometimes crystallized, and in 
the red light-green spots with or without a purple rim. Both red and green slates 
are frequently speckled with lenses (see p. 11). The bedding planes are often cov- 
ered with glistening annelid trails and with possible impressions of algre. Thin films 
of barite and calcite occur on the joint planes. 
The location of the more important red slate quarries in the towns of Granville and 
Hampton are shown on PL XX. The structure at two of the quarries is shown dia- 
gram mati call y in figs. H of PL XXIII and £7 of PL XXIV, and the compass courses 
at the more important quarries, with reference numbers to their location on the map, 
JPL XX, are given below, but Nos. 33, 39, 41 lie west of the area mapped; 33 is 3| 
miles north-northeast of Middle Granville, in Granville township; 41 is 2f miles 
a See map forming PI. XIII in Nineteenth Ann. Rept. U. S. Geol. Survey, pt. 3; also the Economic 
iOlosrv and structure section sheets of the forthcoming Mettawee and Fort Ticonderoga lolios. 
