On the Metamorphic and overlying Rocks of Loch Maree. 151 



from F.W. to S.E.. varying occasionally to X. and S. ; and they dip 

 generally at a high angle and are ranch contorted. Besting nncon- 

 formably upon this gneiss series, and forming here the npper 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 AVales. and which he thinks must have 

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

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

 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 unconformably 

 by the quartzites of Crag Roy. (These quartz rocks are also beau- 

 tifully exhibited on Ben Bay, to the south of Loch Maree, and rest- 

 ing 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. Bpon 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 limestone, however, at 

 some distance from the mass being in a comparatively 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 the upper series 

 of rocks, the so-called Upper Gneiss, ftb. The author, however, found 

 another series of sandstones, calcareous grits, and blue flags beyond the 

 main intrusive mass, and occupying a considerable portion of the gra- 

 dually descending groundbetween the river andthe heights on each side. 

 These were also penetrated by another arm of the granite, but, as in 

 the case of the limestone, with the sole result of altering them near 

 the junction. Prof. Xicol places a fault at this point, and says that 

 the fundamental gneiss is here brought up to give an appearance of 

 overlying conformably the unaltered series. The author, however, 

 holds, with Sir B. Murchison and Mr. Geikie, that the next is a 

 younger series, and that it truly overlies the unaltered beds : but he 

 entirely demurs to the view held by them that these should in any 

 way be caUed gneiss rocks, or associated in any way with beds 

 which have undergone the metamorphic change so characteristic of 

 the pre-Cambrian rocks as known in this country, and which could 

 only be induced, he believes, by great depression combined with 

 heat, moisture, and pressure. On examination he found these upper 

 beds everywhere unaltered, except near dykes; and the change there 

 induced in them was that now well known as contact-alteration, 

 and which is so entirely distinct from true metamorphism. These 

 beds aU dip to the S.E., and attain a thickness of several thousand 

 feet. They are flag-like in character, are made up chiefly of 

 fragmentary materials, and are occasionally even slightly calcareous. 



