ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 151 



ore have been raised. Beyond Deerpark the outcrop is seen in 

 Penhallow Moor and apparently much farther, but no important 

 openings have been made upon it. 



The general characteristics of the great lode appear to be 

 somewhat as follows. It occupies a very distinct and unusually 

 wide fissure which cuts through the stratified rocks, and 

 also through several intrusive dykes of elvan. The upper 

 portion underlies somewhat more — the deeper workings, so far 

 as yet seen, somewhat less than 45" to the southward. The 

 width of the fis.sure and of its contents varies greatly, occasionally 

 a few inches, or even less, very frequently from 3 or 4 up to 20 

 feet, occasionally as much as 40 or 50 feet, and perhaps more.* 

 The upper portion is essentially a " gozzan " of compact or 

 cellular brown hematite, sometimes containing kernels of 

 chalybite, — at times there is very little quartz, at others the 

 whole mass is highly siliceous. Beneath the brown hematite — 

 sometimes only a few fathoms from surface — and always before 

 the sea level is reached, the lode appears to be largely composed 

 of spathose carbonate of iron (with occasional broad belts of 

 dark compact blende, and much more rarely veinlets of yellow 

 copper ore) or of galena. On the whole the carbonate of iron 

 is most abundant in the foot-wall, the blende in the central 

 or upper parts. 



In the wider portions of the lode the filling is a mass of 

 breccia, enclosing large masses of carbonate of iron and of blende, 

 and Mr. Smyth in 1881 gave sketches of two of the deeper 

 workings shewing this mode of occurrence. Thus near the hot 

 cross-cut at the 60 referred to in the foregoing note, the lode lies 

 very fl.at, and consists of (a) a broad band of white clayey 

 carbonate of iron on the foot-wall, this is succeeded by (h) a 

 mass of mixed iron pyrites and flucan, (c) a thick mass of the 

 breccia referred to, containing especially in its upper portions 

 large lumps of dark blende. In other parts bands of red and 

 brown or black iron oxides and of quartz vein-stone are frequent, 

 — the black oxide containing ziac and manganese with some- 

 times copper, — in tact manganese is present almost everywhere. 



*The widths sometimes stated of 100 feet or even mox'e are horizontal sections 

 across an inclined lode, and therefore misleading. 



