ON THK AllCir.EAN HOCKS OF GUEAT IIRITAIN. 



545 



iU the 

 he late 

 jlan(;cs 

 lid the 

 of tho 

 avas of 



mei'ous 

 (f tliest 



11 thirty 

 1 was so 

 truce of 

 c limiteil 

 ils of tlic 

 s of the 

 lain liody 

 2V of the 

 ;amorpliie 

 This, tlu" 

 ' tlifTcrciit- 

 tics recall 

 st ancient 

 locality in 

 geological 

 icikic, tk 

 consist ol 

 •nblendfc- 

 sericite- 

 enclo?e 

 •d, from 

 ancient 

 ilds, the 



oarli 

 ,(r great 



o\e ino''*-' 

 Above 



r.etirac^ 



Itone. Thi^ 



|)(1SCll ti' 



ractically 



roup ot 

 lti> 



Icvlyini^' 

 is con- 



;.ian linif- 



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

 &c., called by Alurchison the Newer Gneiss series, characterised generally 

 hv 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 nnd northern. 



It was contended by the late Sir K. Alurchison — and the view is upheld 

 by his I'ellow-labourer and successor, Ur. A. Geikie, and has been ever 

 since consistently maintained by the Geological Survey — th..t these 

 Viewer' or 'eastern' gneisses distinctly overlie the group of qnartzites 

 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 j)ossibility of the reappear- 

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

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

 posed by Dr. Hicks, Dr. Callaway, and otlu'rs, who maintain that almost 

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

 more ancient than tlie ' Torridon sandstone,' and are A.rcha^an, though in 

 t!ic main they belong to a newer part of that scries than the typical 

 Hebridean group. 



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

 grapliy 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 similiir regions during the last few 

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

 inorphic rock being of post-Archa3an age. 



(2) That great caution is needeil in applying tlio principles of 

 lowland stratigraphy to the Highlands, which is evidently an ancient 

 mountain region — viz., that the observer nnxst bo prepared, not only for 

 faulting and folding on a grand seal ■ but also for gigantic inversions and 

 overthrnsts. 



Within the limits of this snmmary it will not be possible to diocuss 

 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 grou}), and the facts 

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



it is of cour.se universally admitted that thei'e is a vast break between 

 the Torvidon sandstone and the Hebvidi an 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 qnartzites) is in close sequence 

 with and is followed })y the limestone. 



The views, then, arc the following : — 



(1) That the eastern gneiss' follows in con formal )le succession with 

 the limestone that overlies the (piartzitcs ; that, as these are Ordovician, it 

 too cannot be earlier than that pci'iod (Murchison, Geikie, and the 

 ih'itish Geological Survey). 



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

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

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



(•^) That the eastern gn('i.>-s is newer than the limestone overlying 

 tlic rjuartzite, but that this is not identical with the fossiliforous lime- 



1SS4. 



' I think this term prdVi at K-, as not involviiiL' any tlioorv. 



X N 



