xviir BRIEF OUTLINE OF RESULTS. 



primeval rock is exposed iu California. Tbe lavas burst through the granite, and the conclusion is 

 reached that they cannot possibly consist of remelted sediments. 



The historical and structural geology of the quicksilver belt is discussed in Chapter V. It is 

 shown that the metamorphosed rocks pass over into early Cretaceous beds containing a very charac- 

 teristic fossil of the genus AuceUa. Soon after the era in which this mollusk lived — the Neocomian — 

 occurred the great upheaval which iuduced the metamorphism. The next strata iu point of age com- 

 prise a hitherto undetected group of the middle Cretaceous called the Wallala beds. They were laid 

 down uncouformably on the already metamorphosed Neocomian. At the very end of the Cretaceous 

 the Chico series were deposited for the most part on the metamorphic rocks and uncouformably with 

 them. Following the Chico are the T^jon beds, whic]^ are here regarded as Eocene; but there was 

 continuity of life and of sedimentation from the Chico to the Tejon, or from the Cretaceous to the Ter- 

 tiary — a state of thiugs detected nowhere else in the northern hemisphere. Upon the T^jon lie the 

 Miocene rocks with no notable nonconformity. The close of the Miocene was marked by an impor- 

 tant upheaval, which was recognized by earlier observers. The volcanic period seems to have begun 

 ue.arly at this time. The end of the Pliocene was also marked by disturbances, aud most of the asper- 

 ites seem to have been erupted at this epoch. The ore deposits stand in close relation to the volcanic 

 phenomena and are probably nearly or quite all Post-Pliocene. 



The gold belt of California contains JHce??a-bearing beds in Mariposa aud Tuolumne Counties. 

 This shell is of the same species as that iu the Coast Ganges, and the first known upheaval of these 

 mountains was contemporaneous with an important addition to the Sierra Nevada. A description of 

 various forms of AuceUa from different portions of the world, by Dr. C. A. White, with plates, forms an 

 appendix to this chapter. 



Descriptive chapters follow dealing with the various districts of which detailed surveys were made. 

 Each of these districts afJ'ords special facilities for the study of some special topic. The Clear Lake 

 region contains fresh-water Pliocene beds, and in it the age of the andesites can be determined. It 

 also contains remarkable areas of volcanic glass. At Sulphur Bank ciuuabar is being precipitated from 

 heated waters largely by the action of ammonia. At Knoxville, besides the ore deposits, there are 

 admirable opportunities for determining the age of the metamorphic rocks and for studying the process 

 of alteration. At New Idria the nonconformity between the metamorphic rocks and the Chico and the 

 continuity between the Chico and T^jon appear. The New Almaden mine is particularly well adapted 

 for the study of the structure of the ore deposits. At Steamboat Springs cinnabar is being deposited 

 without the complications iutroduced by the prescuce of ammonia. 



In Chapter XII the Great Western, Great Eastern, and Napa Consolidated mines are described, aud 

 in the next chapter more or less informatiou is given concerning each of over fifty minor deposits on 

 the Pacific slope. Some of these have been productive mines, while others are mere prospects or possess 

 only a geological interest. 



A general discussion of the deposits described follows, including the enumeration of the gangue 

 minerals, the microscopical character of ores, etc. It appears that the cinnabar has been deposited 

 solely in i)re-existiug openings, and never by substitution for rock. The fissure systems, which are 

 always present, are very irregular, and deposits cannot be conveniently classified according to existing 

 systems. A new descriptive term, " chambered vein," is suggested, which would include nearly all 

 the deposits. A chambered vein is defined as a deposit consisting of an ore-bearing fissure and of ore 

 bodies contiguous with the fissure which extend into the country rock. It appears that all of the 

 deposits described have probably been deposited in the same way from hot sulphur springs. 



Chapter XV deals with the pi-ocesses by which the ore has been dissolved and precipitated in 

 nature. It is shown by experiment aud aualysis tliat cinnabar unites with sodium sulphide in various 

 proportions, forming soluble doublo sulphides, and that these compounds can exist in such waters as flow 



