60 
SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
Use of slate in Portland cement manufacture. — Slate is merely a form of shale in which 
a fine, even, and parallel cleavage has been developed by pressure. In composition, 
therefore, it will vary exactly as do shales, and, so far as composition alone is con- 
cerned, slate would not be worthy of more attention, as a Portland cement material, 
than any other shale. 
Commercial considerations in connection with the slate industry, however, make 
slate a very important possible source of cement material. Good rooting slate is 
relatively scarce and commands a good price when found. In the preparation of 
roofing slate for the market so much material is lost during sawing, splitting, etc., 
that only about 10 to 25 per cent of the amount quarried is salable as slate. The 
remaining 75 to 90 per cent is of no service to the slate miner. It is sent to the dump 
heap, and is a continual source of trouble and expense. This very material, how- 
ever, as can be seen from the analyses quoted below, is often admirably adapted for 
use in connection with limestone in a Portland cement mixture. As it is a waste 
product, it could be obtained very cheaply by the cement manufacturer. 
Only one American Portland cement plant is at present using roofing slate as one 
of its raw materials, and this plant is of recent construction. It is that of the South- 
ern States Portland Cement Company, and is located about half a mile east of Rock- 
mart, Ga. The Portland cement manufactured here is made from a mixture of pure 
limestone and slate, both of which materials occur in the immediate vicinity of the 
plant. 
East of the town the surface rock is the "Chickamauga limestone," which here 
contains beds of pure nonmagnesian limestone, which have been quarried at several 
points in the vicinity and burned into lime. 
The cement company purchased the property of the old Georgia slate Company, 
about half a mile southwest of Rockmart, and carried on extensive operations with 
the diamond drill. The intention was to quarry the slate, sell as slate the portions 
best suited for that use, and utilize the scrap and w r aste in the manufacture of cement. 
The quarries from which the limestone is obtained are located half a mile east of 
town, near the mill. 
Analyses of slate used for Portland cement, Rockmart, Ga. 
Silica (Si0 2 ) 57.40 
Alumina ( AloO-j) 
Iron oxide (FeO) 
Lime (CaO) 
Magnesia (MgO) 
1. 
2. 
57.40 
58. 20 
'23. G5 
18.83 
1. 15 
5.78 
3.23 
4.35 
3.23 
3.51 
Alkalis (K 2 0, Na 2 0) (a) 3.20 
Sulphur (S) I (a) .49 
Carbon (C) | («) .82 
Carbon dioxide (CO.) !l , J .60 
Water I G ' 8 ° I 4.07 
a Not determined. 
1. J. F. Davis, analyst. Privately communicated. 
2. Slocum and Vandeventer, analysts, Eighteenth Ann. Rept. U. S. Geol. Survey, pt. 5. 
MAINE. 
By T. Nelson Dale. 
The slate region of Maine lies about in the center of the State, in the southern 
part of Piscataquis County, south and southeast of Moosehead Lake and east and 
west of Sebec Lake, in the towns of Monson, Blanchard, and Brown ville. (See map, 
fig. 4. ) Commercial slate occurs also in the town of Forks, Somerset County. 
Geological relations. — The slate occurs in a belt consisting largely of slaty rocks, 
represented by Prof. Charles H. Hitchcock as from 15 to 20 miles wide, and extend- 
