84 
SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
GEOLOGICAL RELATIONS OF SLATE. 
In view of the origin and structure of the marine sedimentary slates it is evident 
that such slate deposits are to be looked for along the borders of or in proximity to 
granitic land masses where the dominant pressure has come mainly from one direc- 
tion and where it has not been sufficiently intense to result in extreme metamor- 
phism. The Maine slate belt lies not far south of a granitic area. Two of the 
Vermont slate belts lie but a few miles west of the Green Mountain granitic axis 
and two others east of it. In eastern Pennsylvania, West Virginia, and Maryland 
the slates lie not far northwest of a granitic area, and the Virginia slate lies not 
many miles southeast of one. 
From the facts brought out in considering the structure of slate it is also evident 
that slate belts generally bear evidence of more than one crustal movement. Along 
the entire Appalachians, where at least two major mountain-making movements 
occurred — the Ordovician and the Carboniferous — and where the slates are mostly 
of Cambrian or Ordovician age, they must needs show the effect of at least one 
disturbance of the slaty cleavage. 
Where, as in western Vermont and eastern New York, slates of two geological 
periods occur in proximity, and where one is even superposed on another, the ques- 
tion of their mutual relations becomes of economic and scientific importance. « 
There was here a crustal movement at the close of Lower Cambrian time which 
resulted in the cleavage of the Lower Cambrian sediments and their emergence. 
They were afterwards, in places submerged and received Ordovician deposits, which, 
at the close of Ordovician time, were folded and also received a slaty cleavage. 
Moreover, the folds of both periods are overturned. 
CHEMISTRY OF SLATE. 
CHEMICAL COMPOSITION. 
Comparatively few complete chemical analyses of roofing slates have found their 
way into scientific literature. Several of the rare elements are usually omitted. FeO 
and Fe 2 3 are not distinguished, nor CaO and C0 2 , so that several of the percentages 
are more or less misleading. Fourteen selected analyses, all but one from European 
sources, are here given for reference: 
Selected analyses of roofing slates. 
I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
VIII. 
IX. 
X. 
XL 
XII. 
XIII. 
XIV. 
Si0 2 (silica) 
58.30 
61.57 
65.63 
61.43 
67.56 
59.35 
55. 880 
55.06 
60.68 
60.17 
56.71 
56.92 
57. 23 
63.06 
Ti0 2 (titanium di- 
.23 
1.31 
.94 
.73 
1.00 
L.270 
.59 
1.15 
.70 
.90 
.89 
.73 
A1 2 3 (alumina) 
21.89 
19.22 
20. 20 
19.10 
12.23 
13.56 
21.849 
22.55 
21.20 
18.89 
14.43 
16.41 
20.43 
18.03 
Fe 2 3 (ferric oxide) 
7.05 
6.63 
2. 72 
4.81 
2.87 
1.10 
1.97 
5. 68 
6.17 
1.98 
.53 
1.33 
2.24 
FeO (ferrous oxide) 
2. 57 
1.20 
• .85 
3.12 
6.99 
4.75 
9.033 
5.96 
.46 
.95 
3.65 
3.52 
5.64 
4.07 
CaO (lime) 
.39 
.22 
.19 
.31 
.27 
5.20 
.155 
1.30 
1.71 
1.75 
3.83 
2.94 
1.54 
.81 
BaO (baryta) 
.04 
.04 
.03 
.02 
MgO (magnesia) . . . 
1.09 
2.00 
1.54 
2.29 
3.03 
3.60 
1.495 
2.92 
.88 
1.85 
3.47 
3.14 
2.49 
2.21 
KoO (potassa) 
2.45 
3.63 
3.81 
3.24 
1.76 
1.77 
3.640 
3.82 
3.64 
2.76 
2. 61 
3.27 
2.39 
3.07 
Na 2 (soda) 
1.18 
.93 
.71 
.83 
1.28 
1.48 
.460 
2.17 
2.09 
1.39 
2.59 
1.47 
3.97 
1.51 
C0 2 (carbon diox- 
ide) 
4.45 
1.04 
3.71 
.77 
2.68 
1.54 
C (carbon) 
3.11 
1.794 
.07 
aSee Am. Jour 
Sci., 
4th s 
er., v 
Dl. 17 
1904, 
p. 185 
, and 
Bull. 1 
I. S. G 
sol. Su 
rvey, 
No. 2 
12, 190 
