462 E. B. Andrews—New and interesting Coal Plants. 
Clay has not been pierced, good grounds (presence of included 
syenite and absence of included propylite) exist for believing 
that the hanging wall is syenite :—that although the east coun- 
try syenite has been pierced in a number of places, both verti- 
eally and horizontally, to a depth of several hundred feet, no 
other formation has been reached, nor any indication that the 
limits of this have been approached; on the contrary, this east- 
ern syenite is apparently as solid as Mount Davidson itself:— 
that wherever the relations between the walls of the fissure have 
been most completely exposed, the occurrence of syenite on the 
— wall is accompanied by a very decided increase in the angle 
of dip. 
The last point is most clearly shown in the Ophir, where on 
the 1700 feet level the walls are almost exactly perpendicular, 
as shown by the very complete prospecting on that level. 
The Gold Hill mines seem nowhere to have reached the sy- 
enite, as was to be expected, since from the conformation of the 
country, the syenite, if it underlies the porphyry in Gold Hill 
as well asin Virginia, will probably be met with only at a much 
greater depth. 
To establish the exact line of the passage of the vein from the 
propylite into the syenite, would of course require a specially 
authorized examination of the mines; since a-majority of points 
in which the east wall has been struck are hidden from view, 
either by the closure of drifts no longer essential to the working 
of the mines, or by timbering in the shafts, ete. 
Many important deductions might be based upon a change 12 
the conditions of the Comstock lode, which must be fraught with 
exceedingly imporiant consequences to the greatest mining 1D 
terest of the Pacific coast; but I prefer to confine myself to sub- 
mitting the fact of this remarkable, and at this time most unex: 
pected, alteration in the character of the vein. 
Berkley, California, October, 1875. 
Art. LVIL—Notice of New and Interesting Coal Planis; by 
KE. B. ANDREWS. 
[Read at the Detroit Meeting of the American Association. ] 
_ Two or three years ago, I noticed in a ditch by the roadside 
in the western part of Perry county, Ohio, a thin layer of bitu 
minous shale. Its stratigraphical position is near the base of ne 
Ohio Coal-measures, perhaps thirty feet above the Maxvil if 
limestone, the Ohio equivalent and representative of the Ches- 
_ ter limestone of Illinois. A few strokes of the hammer et 
vealed a fragment of a coal plant entirely new to me. This lee — 
to subsequent visits to the locality and the discovery of a large 
