274 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



least be shown that they possess a certain degree of uniformity ; for, though 

 there may be gradual changes from point to point in a mass which has been 

 reduced to a pasty state by imperfect fusion and which has been extruded 

 through vents, a certain degree of homogeneity, more easily appreciated 

 than described, is inevitable. This is entirely lacking in the rocks at Knox- 

 ville, which often change from one structure to another in the most capri- 

 cious manner and wliich frequently pass over into little altered, clastic rocks. 

 Though there are single specimens and blocks of rock which might be sup- 

 posed eruptive, the greater part of the rocks are not comparable with gneiss 

 or with any eruptive rock and are manifestly closely allied to sandstones and 

 slates such as no one would think of considering eruptive. As has already 

 been remarked, no case of interbedded Pre-Tertiary eruptives has been met 

 with in the investigations described in this volume nor any instance in which 

 the serpentine is eruptive or traceable to the alteration of an eruptive rock. 



These rocks not crystalline precipitates — Tlic suppositiou that the grauular aud ser- 

 pentinoid rocks, though sedimentary in their origin, were originally depos- 

 ited in approximately their present condition also requires careful consider- 

 ation, particularly, as this appears from the published evidence to be the 

 most probable explanation of the genesis of some similar rocks in other 

 parts of the world. Were this the case at Knoxville, two possibilities would 

 present themselves : Either the conditions necessary to the deposition of the 

 crystalline rocks must have been general, in which case the ordinary sedi- 

 mentary strata of the district are of a different age, or, on the other hand, it 

 might be that the ordinary sediments and the crystalline rocks are of the 

 same age and that local influences produced the differences in lithological 

 character. 



The granular and serpentinoid rocks of the Knoxville district are of 

 the same age as the ordinary soft, fossiliferous sandstones and shales, and 

 this is shown independently by the structure of the country and by the 

 transitions between the two classes. The structure can be particularly well 

 studied in the neighborhood of the Reed mine, on the north branch of 

 Davis Creek. To the nortliwest of the mine lies an area of unaltered rocks 

 carrj'ing Aitcella ami otiier fossils; another and larger area, also carrying 

 AnrcUa, extends in a southwesterly direction from a point about one thou- 



