508 H. H. Davison—Primary Zones of Cornish Lodes. 
The close connexion between the predominance of copper and the 
granite is shown by instances of lodes passing from slate to granite 
into slate again, the copper always being predominant in the slate 
and the tin on the oranite. 
THE WoLFRAM ZONE. 
As mentioned above, the place of copper is sometimes taken by 
wolfram, which occupies a similar relative position in the lode. It is 
probably not accidental that all the wolfram-producing lodes are 
found in the neighbourhood of ridges or minor domes (“ cupolas ”’) 
of the granite. In such ‘position the wolfram may be found either 
in the clay slate, as at Castle-an-Dinas and Killifreth, or just inside 
the granite, as at Hemerdon and Kit Hill. It may also occur in 
lodes passing from the slate into the granite, as in the case at Tin 
Croft Mine, Roger’s Lode, East Pool Mine, etc. The lodes are of 
coarser texture than usual, and sometimes show a pegmatite-like 
structure, the chief minerals being quartz, chlorite, muispickel, 
wolfram, and cassiterite ; tourmaline is not usually present in large 
quantities, fluorspar is often present, and molybdenite, stannine, 
and pyrite are occasional constituents. The wolfram content 
decreases and the cassiterite increases as the lode is followed from 
the slate into the granite either in depth or horizontally. 
THE Coprer-TIn ZONrE. 
In most cases the copper zone of a lode passes downwards into 
a zone in which the lode carries both copper and tin in fair 
proportions. This zone is perhaps more correctly described as a 
passage zone from the zone of predomimant copper to that of 
predominant tin, but it is often so clearly marked and has produced 
so much ore in many mines, that its classification as a separate zone 
is perhaps justified. 
In the various districts the position of the zone is as follows :— 
Depth of Base of Cu Sn 
District. zones in Fathoms. Position of Area. 
Average. | Maximum. 
Camborne and Redruth 180 | 300 On flank of granite mass. 
Gwennap . : : — —- Away from granite mass. 
Wendron . : : 50 100 Heart of granite mass. 
Crowan : ‘ : 150 — | Flank of granite mass. 
Gwinear. : : 200 — In area of contact altered 
slate away from granite. 
St. Day  . : 6 150 — Plank of granite mass. 
The composition of the lode-stuff is similar to that of the copper- 
zone, but mispickel is more common, and tourmaline is present in 
greater proportion. The veinstone generally appears under the 
microscope as well-crystallized, with quartz, chlorite, mica, 
tourmaline in well-formed blue and brown prisms, chalcopyrite, 
