106 J. H. Teall — Cheviot Quartz- FeUites and An gite- Granites. 



claim them as Silurian. At present the disproof of the " visible 

 ascending succession " of the Murchisonian party is a brilliant 

 triumph for the Nicolites. But the truth lies, I cannot help believing, 

 between the two views. If I can prove my case, we shall find : — 



(1) That there is no I'ecognizable chronological sequence (or in- 

 variable succession of superposition) in the metamorphic Highland 

 area corresponding to that among the sedimentaiy formations (for 

 the planes dividing the truly metamorphic layers are not planes of 

 deposition, but planes of shearing and cleavage). 



(2) Many of its (the Highland) schists are composed of Archaean 

 materials (rocks), which have received their present pseudo-bedded 

 arrangement since Ordovician times. 



(3) What proportion of its schists and gneisses is composed of 

 Archasan, sedimentary, or intrusive materials respectively is in all 

 probability an insoluble question. 



(4) Its gneisses may be either Archaean or (some) possibly formed 

 hj intrusion (injection of plutonic rocks) in later ages. 



(5) Its schists may be composed either of crushed Archaans, 

 crushed intrusives, or of a mixture of these with sedimentaries. 



(6) Its (so-called) slales may be (according to the locality, either 

 normal slates or) crushed rocks not yet crystallized (and) of either 

 Archgean, sedimentary, intrusive, or of mixed origin. 



II, — On some Quaktz-Felsites and Augite-Geanites from the 



Cheviot District. 



By J. J. Harris Teall, M.A., F.G.S. 



IN previous communications to the Geological Magazine ' I have 

 described at some length the petrographical characters of the 

 lavas and tuffs of the Cheviot District. It was proved that they are, 

 at any rate for the most part, of an andesitic character, and that some 

 of them are so little altered as to be thoroughly entitled to the 

 term andesite, unless we are prepared to adopt the unphilosophical 

 system of making geological age, per se, a factor in petrographical 

 nomenclature. If we leave out of account the modifications in 

 structure and composition which have been superinduced on the 

 i-ocks by the various agents of change, then the Cheviot lavas and 

 tuffs belong to the three fairly well characterized groups of the 

 augite-, hypersthene-, and mica-andesites. 



It is interesting to note that pumice and ash having essentially the 

 same chemical and mineralogical composition as the Cheviot hyper- 

 sthene-andesite was erupted in immense quantities by the volcano of 

 Krakatoa in the autumn of last year : a fact which testifies in a 

 striking manner to the uniformity in volcanic phenomena during 

 immense periods of geological time. 



In the present communication 1 propose to describe some intrusive 

 rocks that occur in the Cheviot district. They belong to two well- 

 marked groups — the quartz-felsites and the augite-biotite-granites. 



^ Notes on tlie Cheviot Andesites and Porphyrites, Geol. Mag. 1883, pp. 100, 

 145, 252. 



