1 882. I'J'l Trans. N. Y. Ac. Set. 



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 

 PhiLidelphia 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 tault-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 Hne of 

 fracture. The sulphur in 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 



