124 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
The given results, with the exception of those for softness, may be compared with the results for 
Bangor, Pen Argyl, Lehigh, and Peach Bottom slates, given in my papers published in Transactions 
of American Society of Civil Engineers for September, 1892, and December, 1894, and in Stone for July, 
1898. The results above given for softness are comparable with each other, but can not be compared 
with those in the papers cited; this is due to the circumstance that the former grindstone has been 
destroyed by fire and that the one selected to replace it has a much smaller abrading capacity. 
Mansfield Merriman. 
South Bethlehem, Pa., July 2i, 1905. 
COMPARATIVE CHARACTERISTICS OF SLATES. 
The following table shows the principal mineralogical, chemical, and physical 
characteristics of 38 kinds of slate described by the writer in this bulletin as far as 
these manifestly bear upon their economic value. These slates are from Arkansas, 
California, Maine, Maryland, New York, Pennsylvania, Vermont, Virginia, and West 
Virginia. For full particulars and for scientific details the descriptions should be 
consulted, by reference t<> the pages given in the first column. The columns headed 
"strength" and "toughness" refer to the tests by Merriman, whose methods of 
experimentation are described on page 47. Microscopic texture refers primarily to 
the matrix or body of the slate. By "crystalline" is meant that the matrix consists 
of interlacing and overlapping scales and fibers of muscovite and is, therefore, a mica- 
slate or technically a pliyllite-slate, although it may inclose unaltered particles of sedi- 
mentary origin. Such a slate should have, other things being equal, greater elasticity 
(toughness) and strength than one in which there is no such texture, or in which it is 
only incipient. The fineness or coarseness of this crystalline texture probably has a 
bearing upon the strength and toughness of the slate, but physical data are not suf- 
ficient to show this. The coarse-textured Peach Bottom slates, which really approach 
a mica schist, are the strongest of the twelve kinds of American slates tested, but they 
are less flexible than all the other kinds tested. In the grade of fissility 1 signifies 
a perfect slaty cleavage, 4 a very imperfect one. The column of chief mineral con- 
stituents includes only the four or five principal ones seen under the microscope, or 
w Ik >se presence has been otherwise determined, and these are given in the descending 
order of their probable abundance. 
To these comparative data should be added the results of a few tests not easily 
tabulated. 
M»rriman's later corrosion tests showing the following percentages of loss in weight 
after immersion in acid solution for 360 hours: Pennsylvania slates, 1.68 to 2.76; 
Peach Bottom, 1.11 to 1.29; red of New York and Vermont, 0.25. During this test 
the Pennsylvania slates become a grayish white, some of the Peach Bottom slates 
change but slightly, others are almost unaffected; the red slates likewise remain 
almost unaffected. a 
E. H. S. Bailey's tests of porosity give these indices of porosity: "Hard Vein" 
Pennsylvania Chapman, 0.11-0.14; Daniels quarry, 0.14; Belfast quarry, 0.25; red 
of New York and Vermont, 0.21. & 
J. F. Williams's tests of the compression of columns of slate 10 inches long by an 
inch in section with the cleavage vertical, show that the purplish of the unfading 
green series of Vermont stands 20,000 pounds; the unfading green, 16,020 pounds, 
and the red of New York and Vermont, 17,730 pounds. c 
The following results of various tests of Maine (Monson) slate made at the United 
States Arsenal at Watertown, Mass., were republished from the War Department 
reports in the Twentieth Annual Report of the United States Geological Survey, 
Part VI (continued), 1899, p. 395: 
a Trans. Am. Soc. Civ. Eng., vol. 32, p. 538. 
b Loc. cit., p. 542. 
"Loc. cit., p. 132 (see Bibliography, p. 145 of this bulletin). 
