ORIGIN AND MODE OF OCCURRENCE OF GOLD-BEARING VEINS. 147 



The Bassick Mine in Colorado, in the United States, is certainly 

 •one unequalled for its peculiarities in any other part of the world. 

 It consists of a hill of trachyte and felspathic conglomerate 

 about 200 feet above the surrounding country. In this hill is an 

 irregular fissure, elliptical in horizontal section, and about 100 feet 

 long by 20 feet wide ; it has been followed for over 800 feet 

 downwards. The ore in this fissure is composed of concentric 

 layers surrounding individual worn and rounded boulders of 

 country rock. These boulders are from the size of small pebbles 

 to two feet in diameter, and the ore that surrounds them is in 

 three or sometimes four layers. The first layer consists .of 

 sulphides of zinc, antimony, and lead, with about 60 ounces of 

 silver, and from one to three ounces of gold to the ton. The 

 next layer contains more lead, silver, and gold than the last, — 

 frequently as much as 100 ounces of gold, and 150 to 200 ounces 

 of silver per ton. The third layer consists of blend, with from 

 60 to 120 ounces of silver and 15 to 50 ounces of gold to the ton. 

 The fourth layer, when it occurs, is formed of , chalcopyrite 

 (copper pyrites) and varies much. 



Near the centre of the deposit the boulders are larger, and the 

 layers of ore thicken and contain more of the precious metals ; 

 but the boulders gradually become smaller, and the layers of ore 

 thinner and poorer, as the sides of the fissure are approached, 

 until they merge into a pebbly conglomerate in a felspathic base 

 and from thence into the country rock trachyte. 



The interspaces between the boulders are filled with quartz 

 •and tetrahedrite (grey copper ore), and tins quartz has the 

 •appearance of being deposited from solution in a gelatinous state. 

 Graphite occurs in cavities between the boulders. This deposit 

 is thought by some to have been the site of a geyser or mineral 

 spring carrying minerals in solution in its waters. 



The El Callao Gold Mine in Venezuelan Guiana, is one of the 

 richest in the world. It is said to be in felstone, containing 

 pyrites, the quartz of which the gangue consists, being white 

 occasionally tinged with green. I have examined specimens from 

 this mine, and they are very similar to some of the stone taken 

 from the quartz veins in the Australasian Colonies. From 1871 

 to 1879 a total quantity of 67,362 tons of quartz is said to have 

 been crushed from this mine for a return of 252,973 ounces of 

 gold; and in 1880, 18,624 tons of quartz for 54,013 ounces of 

 melted gold. 



The gold of the Ural Mountains is contained in quartz veins 

 in such rock as diorite and serpentine. Deposits of gold are 

 found enclosed in the country rock. The quartz veins in that 

 place are said by the late J. A. Phillips, F.R.S., to be especially 

 interesting on account of the influence exercised upon them by 



