GEOLOGICAL MAGAZINE. 
NEW SERIES. DECADE -V.. VOLES) Vil 
No. VIII.— AUGUST, 1910. 
ORIGINAL ARTICLHS. 
I.—Tue Averen Gyeiss and Morne Sepiments or Ross-SHIRE. 
By C. T. Crover, M.A., C. B. Crampton, M.B., C.M., and 
Je Ss Euerr, MeAc, D:Se: 
(WITH A TEXT-MAP.) 
Communicated by permission of the Director of the Geological Survey. 
N the centre of Ross-shire, to the west and north-west of Ben 
Wyvis, there are large intrusive masses of granite gneiss lying in 
the midst of the sedimentary Moine schists. They have a N.N.E. 
strike and extend over a tract of country about 20 miles in length, 
from Loch Luichart, near (tarve Station (Dingwall and Skye line), 
to Carn Bhren, within 3} miles of Ardgay Station (Inverness and 
Wick line). A coarse augen gneiss with large elliptical eyes of 
pink orthoclase or perthite, sometimes 2 inches long, is the principal 
rock, but a finer-grained granite gneiss also occupies considerable 
areas, especially in the region of Carn Chuinneag (see Map, Fig. 1). 
Boulders of the augen gneiss have been widely distributed by ice, and 
are common on the shores of the Moray Firth, etc. For that reason 
the ‘‘Inchbae augen gneiss”’ has long been familiar to geologists, 
though httle was known about the parent mass, except that gneisses 
of this type were exposed on the high road between Garve and 
Ullapool, particularly in the lower part of Strath Rannoch. 
Since 1900 the work of the Geological Survey has proved this 
augen gneiss to be one of a number of foliated intrusions, perhaps 
originally all parts or offshoots of a single laccolitic mass, surrounded 
by an aureole of hornfelses in which the Moine sediments are intensely 
contact-altered, and have in large measure escaped the subsequent 
dynamic metamorphism which has elsewhere over a vast area converted 
them into the great series of schists and gneisses that are generally 
known as the Moine Series. Elsewhere in all their extent from the 
north coast of Sutherland to the Ross of Mull these Moine rocks are 
paraschists and paragneisses, generally of highly metamorphic types, 
but in this aureole they retain their original bedding and clastic 
structures in singular perfection. It has been proved that when the 
Moine sediments were invaded by the granitic rocks of this region 
they were sandstones and shales of quite normal character; and much 
light has been thrown on the history of the district and the manner in 
which both igneous and sedimentary rocks acquired their metamorphic 
structures. The one-inch map of this country (sheet 93) is now in 
DECADE VY.—VOL. VII.—NO. VIII. 22 
