222 Geological Society. 



crystalline schists and the overlying rocks are described by Prof. 

 Bonney ; and he recognizes amongst them three well-marked types. 

 In No. 1 he includes the Torridon sandstone, the quartzites and 

 the supposed overlying flaggy beds on the east side of Glen Laggan. 

 These are partially metamorphosed ; only distinct fragments are 

 always easily recognizable in them in abundance. In No. 2, the 

 Ben-Fyn type, the rocks are crystalline throughout, being typical 

 gneisses and mica-schists. In No. 3, the Loch-Shiel series, he re- 

 cognizes highly typical granitic gneisses of the Lower Hebridean 

 type. Dr. Hicks failed to find in these areas at any point the 

 actual passage from group 1 to group 2 ; neither did the same rocks 

 belonging to group 1 meet usually the same rocks belonging to 

 group 2. The evidence everywhere showed clearly that the con- 

 tacts between these two groups were either produced by faults or 

 by overlapping. Group 3, placed by Murchison as the highest beds 

 in a synclinal trough, supported by the fossiliferous rocks, the 

 author regarded as composed of the oldest rocks in a broken anti- 

 clinal. They are the most highly crystalline rocks in these areas ; 

 and the beds of group 2 are thrown off on either side in broken 

 folds. These, again, support the rocks belonging to group 1. The 

 author therefore feels perfectly satisfied that the crystalline schists 

 belonging to groups 2 and 3, which compose the mountains in the 

 central areas, do not repose conformably upon the Lower Silurian 

 rocks of the north-west areas with fossils, and that these highly 

 crystalline rocks cannot, therefore, be the metamorphosed equivalents 

 of the comparatively unaltered, yet highly disturbed and crumpled, 

 richly fossiliferous Silurian strata of the southern Highlands, but 

 are, like other truly crystalline schists examined by him in the 

 British Isles, evidently of pre-Cambrian age. 



In an Appendix by Prof. T. G. Bonney, F.E.S., Sec.G.S., on the 

 Lithological Characters of a Series of Scotch Rocks collected by Dr. 

 Hicks, the author stated that he observed in the above series, as he 

 had done in other Scotch rocks lately examined by him, three rather 

 well-marked types : — one where, though there is a certain amount of 

 metamorphism among the finer constituents forming the matrix, all 

 the larger grains, quartz, felspar, and perhaps mica, are of clastic 

 origin ; a second, while preserving a bedded structure and never likely 

 to be mistaken for an igneous rock, being indubitably of clastic origin, 

 retains no certain trace of original fragments ; while the third, the 

 typical " old gneiss " of the Hebridean region, seldom exhibits well- 

 marked foliation. It is sometimes difficult to distinguish between 

 the first and second of these ; but this the author believed to be 

 generally due to the extraordinary amount of pressure which some 

 of these Scotch rocks have undergone, which makes it very hard to 

 determine precisely what structures are original. Even the coarse 

 gneiss is sometimes locally crushed into a schistose rock of compa- 

 ratively modern aspect. The least altered of the above series the 

 author considered to be the true " newer-gneiss " series of the High- 

 lands, but both of the others to be much older than the Torridon 

 Sandstone. 



