MINERALOGY. 



691 



Gouge. This is the soft rock or clay frequently found between the 

 sheet and adjacent wall-rock. 



Bar. The term denotes a band or belt of very hard and unpro- 

 ductive rock, crossing the crevices and sheets. In crossing a bar all 

 sheets become less productive, and are sometimes entirely lost, the 

 crevices usually dwindling to mere seams. Their width varies from 

 a few feet to many yards. 



Wash-dirt, is the name given to the small ore as it first comes 

 from the mine, mixed with small pieces of rock and clay. 



Pipe-Clay. A light colored plastic clay frequently found in the 

 openings and crevices. 



Drift. An underground gallery or roadway. 



MIKEEALOGY. 



There does not appear to have been any absolute and unvarying order in which the 

 minerals of the Lead region were deposited in the mines. The following conclusions 

 are derived from the inspection of the ore as it occurs in place in the numerous mines 

 visited, and from the examination of a great number of specimens; and it is assumed 

 that when crystals of one mineral are coated or covered with another, the overly- 

 ing one is the more recent. The minerals appear to have been deposited in the follow- 

 ing general order : 



GALEKITE. 



SPHALERITE. 



DOLOMITE, CALCITE. 



PTRITE, MAKCASITE, CHALCOPYRITE. 

 BAUITE. 



CALCITE. 



I 



CERUSSITE, SMITHSONITE, MALACHITE, AZURITE. 



The order above given, however, is subject to very numerous and important excep- 

 tions, and is more particularly applicable to crystallized specimens than to heavy ore de- 

 posits. Large bodies of ore frequently consist of galenite, sphalerite and pyrite, so 

 mingled together that no order of deposition can be ascertained. 



In general it appears that the sulphurets of the metals were deposited first, and that 

 the carbonates have been generally if not invariably derived from them. Carbonate of 

 lead (cerussite), when found crystallized, always occurs in connection with galenite; and 

 carbonate of zinc (Smithsonite) is so frequently found graduating into the sulphuret 

 (sphalerite) as to leave but little doubt of its origin from that mineral. 



It seems not improbable that the formation of the carbonate of zinc may even now 

 be taking place in the ground to quite a large extent; especially in such deposits as are 

 not below the water level, or are only periodically submerged. It is a well known 

 fact that the Drybone diggings are usually comparatively free from water, and that 



