Geological Society of London. 327 



regards some of the minor subdivisions, but in relation to the actual 

 age of nearly the whole of the rocks to the east, or those forming 

 the Central Highlands. The older geologists and, more recently, 

 Prof. Nicol, hold the view that the Central Highlands consist almost 

 entirely of the old fundamental (pre-Cambrian) gneiss, or rocks of 

 that age ; whilst others, represented by the late Sir E. Murchison 

 and by Prof Geikie, say that the rocks forming the whole of the 

 Central Highlands are of much later date, and for the most part of 

 Silurian age. In the present communication the author endeavours 

 to show, from results obtained by him recently by a careful ex- 

 amination of a section extending from Loch Maree to Ben Fyn, near 

 Auchnasheen, that the interpretations previously given are in some 

 important points incorrect, and that this has been to a great extent 

 the cause of such very diverse opinions. 



The section described by him runs for some miles along the north 

 shores of Loch Maree, is then continued in a S.E. direction along the 

 heights opposite Kilrochewe and across Glyn Laggan, and then in 

 an easterly direction through the heights on the north of Glyn 

 Docherty to Ben Fyn and the range of mountains to the north of 

 Auchnasheen. 



On the western and for some distance along the north shores of 

 Loch Maree the Lewisian rocks (fundamental gneiss series) are seen 

 to consist chiefly of reddish or greyish gneiss and hornblende- and 

 mica-schists. The strike in these beds is more or less continuous 

 from N.W. to S.E., varying occasionally to N. and S., and they dip 

 generally at a high angle and are much contorted. Posting uncon- 

 formably upon this gneiss series, and forming here the upper part of 

 the mountain Slioch (about 4000 feet high), are the Cambrian con- 

 glomerates and sandstones, made up chiefly of masses of the rocks 

 below cemented together by a comparatively unaltered matrix. In 

 this, however, he found masses of other rocks, very similar to those 

 found in the Cambrians of Wales, and which he thinks must have 

 come from beds of an intermediate age, like the Pebidian series in 

 Wales, and which have either been completely denuded off here, or 

 which must be present in some other area not far distant. These 

 beds are, for the most part, nearly horizontal ; but on the east side 

 they dip slightly to the S.E., where they are succeeded unconform- 

 ably by the quartzites of Crag Eoy (these quartz rocks are also 

 beautifully exhibited on Ben Eay, to the south of Loch Maree, and. 

 resting unconformably on the Cambrian rocks of the magnificent 

 Torridon Mountains). Alternating with these rocks are some of the 

 so-called fucoidal bands, the beds all dipping with a considerable 

 inclination to the S.E. Upon the quartzites are seen the Limestone 

 bands, occupying chiefly the sloping ground on the west side of 

 Glyn Laggan. These are penetrated by a great mass of granitic 

 rock, which produces here considerable contact-alteration, the lime- 

 stone, however, at some distance from the mass being in a compara- 

 tively unaltered state. In all sections across Glyn Laggan hitherto 

 described the mass of intrusive rock is made to penetrate along the 

 bedding, and is supposed to separate the Limestone entirely from 



