1882. 171 Tiyans.iNs, VEVAG ASCE. 
the rock. Judging by the eye alone, much of the tuff contains trom 
ten to forty percent. of sulphur, while in localities the rock is far richer 
than this. Overplacing the tuff are alluvial cones of gravel, that are in 
some places cemented by sulphur in the same manner as the strata of 
tuff beneath, thus showing that the beds now carrying the sulphur have 
acted simply as condensers for the sulphur, which in every case has 
been derived from a deeper source. 
The third class of sulphur deposits—those in which the sulphur forms 
a lining of crystals on the sides of fissures—are illustrated by the 
Philadelphia and Mammoth mines. At the first of these, situated one 
mile north of Cove Creek, the sulphur occurs in drusy crystals covering 
the sides of small intersecting fissures in trachyte. The rock has here 
been much broken along a line of faulting, which may be traced south- 
ward to the top of the Cove Creek crater. The Mammoth mine is of a 
similar character, but found in dark carboniferous limestone. This 
mine is located on the top of the divide between Cove Creek and Dog 
Valley to the northward. While standing on this pass, the line of 
faulting, on which the Mammoth mine is situated, may easily be traced 
southward to the valley of Cove Creek ; and across the valley it is again 
seen as a bold fault-scarp, with a throw to the westward, ascending the 
side of the volcanic crater that we have already mentioned several 
times. The fault crosses this cone just to the east of the summit, 
and has given the eastern slope of the mountain a steeper inclination 
than is shown by the western side. Northward from the Mammoth 
mine the same line of faulting is continued for many miles, and shows 
a recent scarp all along the eastern border of Dog Valley. The fault- 
scarp that ascends the side of the volcanic cone, and also the recent 
scarp in Dog Valley, are the results of slight and very recent move- 
ments along an ancient line of profound displacement. The volcanic 
mountain southwest of Cove Creek has been built over this old line of 
fracture. The sulphurin the Mammoth mine has been deposited in the 
fissures made by the faulting of the strata, and in the seams and open- 
ings between the layers of limestone. The rock on the borders of 
these fissures, beneath the thin lining of sulphur, has been altered to a 
brown earthy mass, to the depth of about half an inch. The mines, 
like the Philadelphia and Mammoth, that have been opened on lines of 
fracture in solid rock, show but little sulphur, and on the whole cannot 
be considered as giving promise of any large deposit below the surface. 
In these mines also the temperature is high, but not so great as at the 
Cleveland. 
The beds of volcanic tuff, in which the sulphur has been deposited, 
probably rest on harder rock that has been fissured, thus allowing the 
sulphur-bearing vapors to escape upwards, as in the case of 
