Reports and Proceedings— Geological Society of London. 98 
is not here dealt with. The normal granite is more or less por- 
phyritic in structure, with large phenocrysts of perthite, in a coarse 
or fine-textured ground-mass of orthoclase, plagioclase, biotite, and 
muscovite. Various micrographic intergrowths occur, indicating in 
some cases eutectics of three or more components. No reliable analyses 
are available, but the rock is provisionally classed as an alkali-granite 
of Hatch’s classification. 
Evidence is brought forward to indicate that the granite is intruded 
along the axis of an anticline, with a strike approximately E. 15° N. 
and W. 15° S., the normal direction for the district. 
The metamorphic aureole is very large, measuring about 6 miles 
from east to west and 5 miles from north to south. This is out of all 
proportion to the size of the visible exposures of granite, and it is 
inferred that the intrusion underlies a large area at a small depth. 
Within this area three distinct rock-types can be recognized, namely, 
(1) black slates, (2) grey flags, (3) grey grits. The metamorphism 
produced in each of these is described in detail, and it is shown that 
the commonly accepted zones of alteration do not hold, since the rocks 
concerned were originally of very different character. ‘The frequently 
described section in the Glenderaterra Valley runs across the strike, 
and includes both black slates and grey flags. The former never 
undergo a high degree of metamorphism, chiastolite being the 
characteristic mineral. The well-known cordierite-mica rocks of 
Sinen Gill are derived from the grey flags, and a very narrow zone 
close to the granite shows garnet and staurolite. The impure grey 
erits of the central band contain cordierite, andalusite, and mica, and 
garnets are only seen close to the contact with the Grainsgill greisen. 
The Carrock Fell intrusion produces little or no alteration in the 
grits, with which it comes into contact for a long distance. 
The phenomena here displayed may be summed up as an example 
of a moderate degree of thermal metamorphism, due to the intrusion 
of a large mass of granite, at a comparatively low temperature, into 
a series of rocks of variable composition, which had previously under- 
gone dynamic metamorphism. The most important minerals produced 
are cordierite, andalusite and chiastolite, biotite and muscovite, while 
garnet and staurolite are only found close to the granite. Owing to 
the variations of lithological composition across the strike, 1t has not 
been found practicable to divide the aureole into concentric zones, but 
the alteration is gradual and progressive towards the intrusion. 
2. ‘The Metallogeny of the British Isles.” By Alexander Moncrieff 
Finlayson, M.Sc., A.O.S8.M., F.G.S. 
The ore-deposits of the British Isles (tin, copper, lead, zine, gold) 
are considered synthetically in their relation to igneous rocks and to 
tectonics. The four major epochs of igneous activity and crust- 
movement in the area were: pre-Cambrian, post-Silurian (Caledonian), 
post-Carboniferous (Hercynian), and Tertiary. A few insignificant 
ore-occurrences, including the stanniferous magnetite in the older 
granite-gneiss of Ross-shire, date from the pre-Cambrian. A group 
of pyritic fahlbands in the Highlands of Scotland, and the wolfram- 
bearing pegmatites of the Grainsgill greisen, date from the Caledonian, 
