PART II— SLATE DEPOSITS OF THE UNITED STATES, 
ARIZONA. 
By T. Nelson Dale. 
A specimen of roofing slate recently received from Arizona by Dr. David T. Day, of 
the division of mineral resources of the United States Geological Survey, came from 
a deposit about 6j miles north of Phoenix, which is said to measure from 800 to 1,000 
feet in width and about 5,000 feet in length. Its examination has yielded the fol- 
lowing results: 
It is bluish gray with a lustrous surface, marked by two sets of minute wrinkles 
that lie at right angles to each other, a coarser set numbering from 25 to 40 per inch 
and a finer one numbering many more. The slate breaks along the finer set much 
more readily than along the coarser set. It has a marked argillaceous odor, shows 
considerable pyrite on the sawn edge, contains but little magnetite, does not effer- 
vesce in cold dilute hydrochloric acid, is sonorous, and has a fair grade of fissility. 
Under the microscope this slate shows a matrix « consisting of muscovite (sericite) 
with a brilliant aggregate polarization. a Cleavage and bedding foliations are par- 
allel, but are crossed by two incipient slip-cleavages (see p. 24 and Pis. VI, XI, .1), 
the plications of which have not resulted in fractures, but which give the slate a 
somewhat schistose structure. The finer of these slip-cleavages has from 100 to 150 
plications to the inch. There is considerable quartz, which appears to be mostly sec- 
ondary. The conspicuous feature, however, is the great abundance of lenses and 
particles of pyrite and hematite. In the cross sections these measure from 0.0043 to 
0.043 millimeters in length by from 0.002 to 0.008 millimeters in width and number 
about 800 per square millimeter. & In parallel section they have irregular angular- 
roundish outlines. 
There are also large plates of muscovite, a few crystals of tourmaline, a few lenses 
or decomposed crystals of (?) up to 0.0425 by 0.025 to 0.075 millimeters and consid- 
erable rutile in very minute prisms. No carbonate detected. 
The constituents of this slate, arranged in descending order of abundance, appear 
to be muscovite (sericite), quartz, pyrite, hematite, kaolin, magnetite, rutile, and 
tourmaline. 
If properly cut with reference to the direction of weakness this may prove a serv- 
iceable slate, but false cleavage is generally objectionable. In this case the false 
cleavages are, however, only incipient. 
ARKANSAS. 
By Edwin C. Eckel. 
LOCATION AND CHARACTER OF DEPOSITS. 
Location — The slate deposits of Arkansas are included in an area of Ordovician 
rocks in the west-central portion of the State. This area is about 100 miles in its 
igreatest dimension from east to west, and varies from 12 to 20 miles in breadth from 
north to south. The towns of Little Rock, Benton, Malvern, Hot Springs, and Mena 
1a For definitions of technical terms see Glossary, pp. 146-147. 
b The square millimeter referred to comprises the thickness of the thin section. 
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