92 MmnfG indtjstey. 



belongs to tlie period of the earliest formation of the silver sulphides, and seems 

 to have continued to a very late period, certainly until after the formation of the 

 latest clays, for there are no important seams which are not more or less 

 impregnated with the small, brilliant crystals of this mineral. Carbonate ol 

 manganese occurs but once, and in that case occupies a position between the 

 main introduction of sulphides and the latest quartz formation. The other 

 carbonates, those of lead, lime, and copper, belong also to this same period. 

 The oxides, of which there are only those of iron and manganese, are wholly 

 superficial products, belonging to the phenomena of the "Iron Hat," and result- 

 ing without doubt from the decomposition of the carbonate of manganese and 

 the sulphides of iron. Of the accidental rare minerals, pyromorphite, which 

 occurred in the Ophir, belongs to the upper levels, and its relations with the 

 other materials were never clearly understood. Horn silver was found by 

 Kiistel in the outcrops of Gold Hill, but there is no information concerning 

 its paragenetic relations. The sulphates are wholly later than the latest 

 introduction of quartz. They occur, first, in the form of selenite ; secondly^ 

 in those soluble sulphates with which the waters of the lode are now 

 so largely impregnated ; and, thirdly, in that important zone of gypsum which 

 occurs in the east country-rock, from a depth of from 600 to 900 feet below 

 ground. From the Ophir to tlie Yellow Jacket this zone is more or less 

 impregnated with gypsum, which occurs filling the cracks and fissures of the 

 propylite, its fibrous crystals arranged diagonally to their surfaces. The distri- 

 bution of the gypsum or selenite is one of the most interesting phenomena of 

 the vein. At four or five places in the middle works of the lode, such as the 

 Grould and Curry fourth, and the bottom of the Fair View shaft, w^ere found 

 beautiful crystals of selenite resting upon the latest quartz, later, therefore, 

 than any of the metallic introductions, unless it be those sulphides of iron 

 which are found in the clays. Natrolite and chabazite, with a rare association 

 of stilbite, occurred in the black dike of the Gould and Curry, and near the 

 bottom of the North Yellow Jacket shaft. A second growth of selenite has also 

 recurred, its crystals resting upon those of the zeolites. The clays were prob- 

 ably completed before this latest introduction of quartz, since certain of their 

 surfaces and cracks are penetrated by it. After this latest quartz the zeolites, 

 and then the sulphates, subsequent to which we have the "Iron Hat" with its 



