ON THE ARCHAEAN ROCKS OF GREAT BRITAIN. 545 



stones comes a series of 'gneiss, mica-schist, chlorite-schist, clay slate,' 

 &c, called by Murcliison the Newer Gneiss series, characterised generally 

 by a marked bedding and general ' flaggy ' aspect, which readily dis- 

 tinguishes it in the field from the normal Hebridean series. These rocks 

 constitute the greater part of the grand hilly mass designated by the 

 name of the Scotch Highlands, central and northern. 



It was contended by the late Sir R. Murchison — and the view is upheld 

 by his fellow-labourer and successor, Dr. A. Geikie, and has been ever 

 since consistently maintained by the Geological Survey — that these 

 * newer ' or ' eastern ' gneisses distinctly overlie the group of quartzites 

 and limestones, and thus are the metamorphosed equivalents of the 

 Ordovician rocks of the southern uplands of Scotland, representing in 

 the main the Bala beds of Wales ; though the possibility of the reappear- 

 ance of sundry bosses of the Hebridean gneiss was distinctly admitted. 

 This opinion, contested by Professor Nicol, has of late years been op- 

 posed by Dr. Hicks, Dr. Callaway, and others, who maintain that almost 

 all the rocks included in the Newer or Eastern Gneiss series are really 

 more ancient than the ' Torridon sandstone,' and are Archaean, though in 

 the main they belong to a newer part of that series than the typical 

 Hebridean group. 



It will be long before all the difficulties of the complicated strati- 

 graphy of the Highlands are solved, but the two following general state- 

 ments will not be denied by any student of the more ancient rocks : — 



(1) That the results of work in similar regions during the last few 

 years has been to diminish the probability of great masses of meta- 

 morphic rock being of post- Archaean age. 



(2) That great caution is needed in applying the principles of 

 lowland stratigraphy to the Highlands, which is evidently an ancient 

 mountain region — viz., that the observer must be prepared, not only for 

 faulting and folding on a grand scale, but also for gigantic inversions and 

 overthrusts. 



Within the limits of this summary it will not be possible to discuss 

 the many questions that have been raised in relation to Highland 

 stratigraphy, but I shall endeavour to state briefly the principal views 

 which have been maintained, the lithology of each group, and the facts 

 which have to be taken into account in coming to a conclusion. 



It is of course universally admitted that there is a vast break between 

 the Torridon sandstone and the Hebridean series, and that the quartzite 

 (whether conformable or not to the latter, and whether there be two or, 

 as is now generally held, only one group of quartzites) is in close sequence 

 with and is followed by the limestone. 



The views, then, are the following : — 



(1) That the eastern gneiss 1 follows in conformable succession with 

 the limestone that overlies the quartzites; that, as these are Ordovician, it 

 too cannot be earlier than that period (Murchison, Geikie, and the 

 British Geological Survey). 



(2) That the eastern gneiss is nothing but a portion of the Hebridean 

 brought up again by faulting, and so is older than the Torridon sand- 

 stone (Nicol, followed, with modifications, by Hicks and Callaway). 



(3) That the eastern gneiss is newer than the limestone overlying 

 the quartzite, but that this is not identical with the fossiliferous lime- 



1 I think this term preferable, as not inyolvinir any theory. 

 1884. * x x 



