A. M. Finlayson—Ore-bearing Pegmatites of Carrock Fell, 19 
which seems always to have crystallized by preference on a nucleus of 
previously formed accessory minerals. In contrast to tourmaline and 
hornblende, it is remarkable to find halos well shown in such minerals 
as augite and muscovite, which are not normally pleochroic. It is 
also an interesting point that halos never seem to occur in minerals 
capable of causing them, a fact which appears entirely in accord with 
the radio-active theory of their origin. Thus there are none round 
the inclusions of zircon in the large orthite crystals of the Jibuyi 
River granite in North-Western Rhodesia, nor does the epidote of 
the same rock show any where it encloses orthite crystals, a feature 
which may also be noticed in numerous other Rhodesian granites, 
e.g. those of the Matopos, Kalomo, and the Zimbabwe Ruins. 
I must mention, in conclusion, my obligations to Mr. G. W. Card, 
of Sydney, who sent me the New South Wales rocks mentioned above, 
and to Mr. A. E. V. Zealley, who kindly brought to my notice the 
Cornish granophyre, also referred to. 
EXPLANATION OF PLATE JY. 
Ordinary type of circular halo round zircon in biotite, breadth about -035 mm. 
In granite of Matopo Hills, Rhodesia. 
2. Halo round irregular zircon inclusion in cordierite, rim of halo darker than 
interior. In granulite of Bodenmais, Bavaria. 
3. Halos round group of zircon crystals in biotite. In granite of Sea Point, 
Capetown. 
4, Halo round zircon in hornblende, breadth about 035mm. In quartz diorite of 
Jahonda, Rhodesia. ; 
. Halos round zircon in tourmaline. In Cornish granophyre, exact locality 
unknown ; slide lent by A. E. V. Zealley, A.R.C.S. 
. Halo partly in biotite and partly in cordierite, round zircon. In granite (near 
contact) of Sea Point, Cape Town. 
- Halo, with dark rim, round zircon in biotite. In biotite granulite, near 
Rhodes’ Drift, Limpopo River, Rhodesia. 
8. Semicircular halo in biotite, not extending into adjacent tourmaline. In granite, 
Sea Point, Cape Town. 
9. Halo, unevenly tinted, round apatite in biotite. In granulite, near Rhodes’ 
Drift, Rhodesia. salt 
10. Halo, with dark rim, round orthite (allanite) in biotite. In granite, north of 
Kahlele’s Kraal, Matopo Hills, Rhodesia. 
11. Halo in biotite, near inclusion of orthite in epidote. In granite, near 
Zimbabwe Ruins, Rhodesia. 
12. Halo, about -04 mm. in breadth, round orthite in hornblende. In quartz diorite 
of Jahonda, Rhodesia. 
(The magnification is about 100 diameters.) 
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V.—Tue Ore-seartnc Prematires oF Carrock FELL, AND THE 
Genetic SIGNIFICANCE OF TUNGSTEN-ORES. 
By A.M. Fintayson, M.Sc., Assoc. Otago School of Mines, F.G.S., Assoc.Inst:M.M. 
Introduction—The wolfram veins in the Grainsgill greisen, near 
Carrock Fell, are an example of ore-bearing pegmatites, a vein-type 
uncommon in the British Isles, and one, moreover, the study of which 
is of much interest in its relation to ore-genesis. The veins have long 
been known, and intermittently exploited for tungsten-ore, but their 
economic prospects are not bright. Of previous workers, Mr. Alfred 
