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14 REPORT OF STATE MINERALOGIST. ;

trict, one from Pittsburg Landing to Somersville, and one from Antioch
to Stewartville. The old buildings and railroads are now dismantled
and little remains to indicate the extent of former operations. There
are three main veins which have been mined in the principal properties,
the uppermost or Clark vein, next the Little vein, and the Black Dia-
mond or lowest. The stratigraphic distance between the Clark and
Black Diamond veins varies from 300 to 400 feet. The Clark vein has
a thickness of 2£ to 4 feet, being nearly all clean coal with a good firm
roof and floor of sandstone. The Little vein is thinner and more irregu-
lar, but reaches a width of two feet of good clean coal in places. The
Black Diamond vein is much thicker, running from eight to eighteen
feet in thickness, but there are many partings of slate and bone, which
would have to be separated if the entire vein is mined. Clay gouge

occurs along the walls, and on account of its character there is consid-
erable swelling and movement, which add to the difficulty and cost of
mining this vein.
Considerable literature has been published on the early coal mining
operations in Contra Costa County. The beds have been described
particularly by Goodyear 1 , and Smith 2 , as well as by others. The
principal references are given in the bibliography herewith.

Southport Land and Commercial Company, 573-576 Mills Building,
San Francisco; E. S. McCurdy, manager. This company owns several
sections of land in the Mt. Diablo field, including the Black Diamond
coal mine. For the past year several men have been steadily employed,
cleaning out, retimbering and otherwise opening up the old Clayton
tunnel. At the time of visit they were in about 1200 feet. The Clay-
ton entry is run south as a crosscut, cutting all three veins. When the
Black Diamond vein is reached the gangway turns east and follows

the vein. As far as opened up on this level, the workings were dry
and most of the timbers in an excellent state of preservation, though

showing evidence of movement and crushing in places. The company
is reticent as to its plans, but stated that many of the mine maps and
records were destroved in the San Francisco fire and that the work
being clone is of an exploratory nature to determine the location of old
workings and shafts that will afford good ventilation. Air is supplied
by a blower at present and a mule is used for tramming.
Modern methods of utilizing coals of this class lead to the belief that
commercial production may again result from the work.

Bibl: State Mineralogist's Reports IV, pp. 14, 267; VI, p. 116;
VII, pp. 117-146; VIII, p. 160; IX, p. 323; X, p. 165; XI, p.
191 ; XII, pp. 43, 64 ; XIII, p. 51 XVII, p. 53 ; U. S. Geol. Sur-
;
vey 22nd Annual Report, Part III, p. 500; Bull. 285-f ; Min.

Resources 1883, p. 20 ; IT. S. Bur. of Mines Bull. 22, pp. 53, 395
Mineral Resources West of the Rocky Mountains by R. W. Ray-

mond, 1874, pp. 39-42; Geol. Survey of California, Vol. II, pp.
3-34 ; Coal Mines of the Western Coast of the United States by
W. A. Goodyear, San Francisco, 1877.

1 Goodyear, W. A., The Coal Mines of the Western Coast of the United States,
1877; State Mineralogist's Report VII, pp. 117-146.
2 Smith George Otis, U. S. Geol. Survey 22nd Annual Report, Part III, p. 500.