OF THE SOUTH DEVON COAST. 23 
I incline further to the opinion that the fault at the junction of the 
two groups is a considerable one, and that the slaty series of Tor- 
cross and Hope Cove was not deposited in immediate succession to the 
southern schists. The former are generally composed of extremely 
comminuted materials; even fine grits are not common, conglomerates 
I never saw. Now the mica-schists especially abound in quartz- 
veins, and contain layers with fair-sized plates of mica. The former 
would furnish pebbles of white quartz, the latter mica flakes, not 
comminuted, because they would be carried for considerable distances 
without much attrition. Hence, if the slaty series derived much of 
its materials from the neighbouring schists, I should expect occa- 
sional conglomerates of rolled quartz, not unfrequent micaceous grits, 
and abundant scales of the latter mineral in the muddy beds. Yet 
in only one of the specimens examined (p. 18) have I found dis- 
tinetly fragmental quartz and mica, and the micaceous constituents 
of the most satiny slates or phyllites are so minute as to render it 
very possible that they are endogenous rather than exogenous*. 
The absence of fossils makes it difficult to fix precisely the age of 
the slaty series of South Devon. Dr. Holl regards the Torcross 
group as newer than the Plymouth Limestone, and so fairly well up 
in the Devonian series; but, at any rate in Cornwall, we can trace 
unmetamorphosed rocks at least as far back as the Ordovician 
series ; so thab we may fairly assume any metamorphic rock in a 
district so near to be considerably earlier than this geological period. 
I think therefore that we may safely regard the South-Devon schists 
as Archean, and as a prolongation of the massif so distinctly indi- 
cated in the Lizard, to which also belonged the gneiss of the Ed- 
dystone f and those granitoid rocks which furnished the pebbles in 
the conglomerate at the Nare Point. 
The physical history of the district of which the south-west of 
England is a fragment seems then to be identical with that of many 
other regions which have undergone great disturbance from lateral 
pressure. ‘he first stage—a very remote and doubtless very long 
one—was the formation of a great mass of more or less crystalline 
rock, in which perhaps-we may discover the usual progression from 
a basal group of granitoid gneisses through more distinctly foliated 
eneisses and strong schists, to a well-bedded and more variable series, 
in which felspar is comparatively rare. The next stage, an up- 
lifting and denudation of this mass; the third, a long period of 
depression and deposition of sediment; and the fourth, a period of 
continued lateral pressure, folding, cleaving, and otherwise modifying 
the rocks affected by it. To this has of course succeeded, as usual, 
another period, characterized chiefly by denudation, which has lasted 
down to the present time. A physical history this, which, with 
* Tt will be remembered that in the slaty series of the district N.E. of the 
Lizard, fragments of metamorphic rocks are found in the associated conglome- 
rate. Quart. Journ. Geol. Soc. vol. xxxix. pp. 9, 10. 
+ See for indications of the occurrence of crystalline rocks in the bed of the 
Channel, papers by Mr. A. R. Hunt,in Trans. Devon Assoc. vols. xi., xii., xiil. ; 
also by Mr, Pengelly, in vol. xi. p. 319. 
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