COMPARATIVE CHARACTERISTICS OF SLATES. 
125 
Pounds 
Maximum fiber stress per square inch 7, 671 
Shearing test per square inch 2, 192 
Ultimate compressive strength per square inch L9, 510 
Coefficient of expansion, 0.000005. 
The relative commercial value of several slates is an index of their physical char- 
acteristics. Mathews, in 1898, gave these prices for slates II by 7 inches, t lire- 
sixteenths thick, per square: Peach Bottom; $4.85; Northampton County, Pa., $3.50; 
Lehigh County, Pa., $3.40-$3.95; Maine (No. 1), $6.40; Arvonia, Va., $3.60; unfad- 
ing green, Vermont, $4.50; red, New York, $11. « 
The following prices per square for slates, No. 1 quality, L6 by 8 inches, I. o. 1)., 
were obtained by Doctor Day from producers for January, L905: Peach Bottom, 
$6.35; Monson, Me., $7.20; red, New York, $11; Bangor, Pa., $5.75; Albion, Pa., 
$5; Pen Argyl, Pa., $4.75; Chapman, Pa., hard vein, $5.25; Slatington, Pa., $4.50 to 
$5; unfading green, Vermont, $4.50 to $5.25; sea green, Vermont, $3.50; Virginia, 
$5 to $5.50. 
In accordance with the scheme of classification of slates given on page 6, most of 
the slates whose characteristics are given on the preceding table are here arranged 
systematically: 
(A) Clay-slates (Fading) Marti nsburg, \V. Va 
(a) Carbonaceous 
(Fading) * 
graphitic 
Lehigh and Northampton counties. Pa. 
Benson, Vt. 
}) Mica-slates < 
(Unfad- 
ing) 
(blackish). 
(b) Chloritic (greenish) . "Sea green," Vermont. 
(c) Hemati tic and Chloritic (purplish). Purplish of Paw- 
let and Poultney, Vt, 
Peach Bottom, Pa. and Md. 
(a) Graphitic or Arvonia, Va. 
carbonace- Northfield, Vt. 
ous (black-) Brownville, Monson, Me. 
ish). North Blanchard, Me. 
West Monson, Me. 
(b) H ematiti c (Granville, Hampton, N. Y.; Polk 
(reddish). I County, Ark. 
(c) Chloritic (greenish). " Unfading green," Vermont. 
(d) Hemati tic 
and chlo- Purplish of Fair Haven, Vt 
ritic (pur- 1 Thurston, Md 
plish). 
STATISTICS OF PRODUCTION, IMPORTS, AND EXPORTS. 
By A. T. Coons. 
PRODUCTION. 
Although slate has been known and quarried in this country, more or less, since 
1750, when we find records of its use in Massachusetts, Maryland, and Pennsylvania, 
and since about 1850 in New York, Vermont, Georgia, California, Virginia, and other 
States, no statistics of production for the entire United States are obtainable for any 
year preceding 1879. 
For the years 1879, 1881, 1882, and 1883 the production is largely estimated. The 
statistics for 1880 are taken from the Tenth Census and are very accurate. The 
figures from 1884 to 1888 are fairly reliable, and from 1889, when the figures are those 
p Maryland Geol. Survey, vol. 2, p. 240. 
