Trans. N. V. Ac. Sa'. 174 % May 22, 



Rabbit Hole has been derived from a deeply-seated source, and deposited 

 from a vaporous condition, in the cooler and higher rocks in which it is 

 now found. Judging from the silicious material that cements the tufifs^ 

 it is evident that the porous rocks, in which the sulphur is now found, 

 were penetrated by heated waters bearing silica in solution, previous 

 to the deposition of the sulphur. These mines occur in a narrow north 

 and south belt, along a line of ancient faulting which is one of the great 

 structural features of the region. The association of faults, with sul- 

 phur bearing strata of tuff, is here essentially the same as at the Cove 

 Creek mines. At the Rabbit Hole mines, however, no very recent 

 movement of the ancient fault could be determined. This absence of a 

 recent fault-scarp, together with the fact that the mines are now cold 

 and do not give off exhalations of gas or vapor, shows that the solfataric 

 action at this locality has long been extinct. 



At all the localities visited, the sulphur has been derived from sources 

 far beneath the surface, from which it has been expelled by heat, and 

 escaped upwards through fissures that were formed along lines of fault- 

 ing, and has been condensed on the sides of fissures and in the inter- 

 spaces of the cooler rocks near the surface. Whether the deposition of 

 the sulphur took place by direct sublimation, or by the decomposition of 

 sulphuretted hydrogen, has not been determined. The date at which 

 the sulphur was introduced into the rocks, where we now hnd it, is in all 

 cases very recent, and at the Cove Creek mines the action is still in 

 progress. 



Work at the Rabbit Hole mines is now being carried forward by a 

 day-shift of seventeen men, the production of sulphur being about six 

 tons per day. The value of the sulphur produced is about forty-five 

 dollars per ton in San Francisco. The sulphur, after being mined and 

 assorted, is placed in upright cast-iron retorts, having a general resem- 

 blance to the common form of blast furnace, with a capacity of about 

 two and one-half tons. When the retorts are charged, the opening at 

 the top, through which the sulphur bearing rock is introduced, is closed, 

 and superheated steam admitted at the side. The steam pressure is at 

 first about seventy pounds to the square inch ; but, as the sulphur begins 

 to melt, the pressure is allowed to subside to sixty or perhaps fifty 

 pounds. When the sulphur melts, it passes through a grate and is col- 

 lected in a kettle beneath the retort, from which it is allowed to flow, in 

 a very liquid brown stream, into a receiving pan with a capacity of 

 about twelve thousand pounds, where impurities that were previously 

 held in suspension are allowed to settle to the bottom. From the re- 

 ceiving pan, the sulphur is run into molds shaped like the frustum of a 

 cone, each of which has a capacity of from two hundred to two hun- 

 dred and fifty pounds. When allowed to stand a few days after cool- 



