De A Oe: Finlayson—Ore-bearing Pegmatites of Carrock Fell. 
The mineral has been analysed by Traube, with the following 
result } :— 
\WOp = 73-Or 
CaO = 19°27 
Total 99°59 
The presence of molybdenum is worthy of note, this constituent 
having been shown by Traube to be almost universally present in 
scheelite. 
The relations of the minerals may be more clearly studied under the 
microscope. The opaque wolframite encloses quartz in thin strings 
along its cleavage-planes, as well as in granular aggregates. Separated 
grains of quartz are often seen to extinguish simultaneously, and at 
other times the two minerals simulate a graphic intergrowth. Again, 
quartz may occur as a thin selvage to the wolfram. The intimate 
association of these two constituents clearly shows close relation in 
order of deposition. While frequently there has been practically 
simultaneous deposition, on the whole the wolframite appears to have 
preceded the quartz. Crystals of arsenopyrite are almost invariably 
deposited on wolfram or formed in microscopic cavities of the ore. 
This sulphide is probably very largely of metasomatic origin. 
The scheelite, in contrast to the wolframite, is remarkably free both 
from arsenopyrite and from quartz. This would be expected from 
the fact that the arsenopyrite is a metasomatic product after wol- 
framite, and the wolframite and quartz were deposited about the same 
time, while the scheelite is clearly of later date. This mineral 
frequently fills cracks in the wolframite, and while the border-line 
between the two minerals is generally sharp, the scheelite is invariably 
deposited or grown on the older mineral. Occasionally the line of 
junction is irregular, and shows a gradual progression of the scheelite 
by replacement of the wolframite. The observed relations leave little 
doubt that the scheelite is metasomatic, although the processes are not 
in every case obvious under the microscope. The order of deposition 
of the minerals was apparently (1) wolframite and quartz, (2) arseno- 
pyrite and scheelite. 
It is to be noted that there are two lime-bearing minerals in these 
veins, namely, scheelite and apatite. The latter was perhaps the 
earliest of all in order of deposition, and it is not clear to what extent, 
if at all, the scheelite has derived its base from this constituent. In 
any case, this occurrence of lime is of interest, since it has been 
pointed out that in the magmatic differentiation of the greisen from 
the biotite granite of Skiddaw there has been a reduction of the 
alkalis and alkaline earths by 50 per cent. The lime in these two 
vein-minerals may then be taken to represent a portion of the surplus 
bases rejected by the greisen during its differentiation and crystal- 
lization, the lime being brought up at a later stage in the last phase 
of the magmatic processes, i.e. in the formation of the pegmatite-veins. 
Tungsten-ores and Metasomatism.—The formation of tungsten-ores 
1 Jahrb. Min., Beil. Bd., 1890, vii, p. 232. 
* Harker, loc. cit. sup., p. 142. 
