24 PROF. T. G. BONNEY ON THE GEOLOGY 
more or less complication, we find in the Scotch Highlands, in 
North and in South Wales, in the Alps, the Pyrenees, and other 
mountain chains. 
The question as to the mutual relation of the members of the 
presumed Archzan rocks of South Devon may be quickly dismissed. 
We have simply to decide whether the chloritic schist is interbedded 
between two great groups of mica-schist, or whether there is only 
one thick mass of the latter, with some thin bands of the same rock 
in the lowest visible part of the chloritic schist. For the reasons 
given above I consider the latter view to be the more probable, and 
regard even the mass of the Bolt Head as simply the upper mica- 
schist repeated by an extremely sharp fold, or rather series of folds. 
IfI were to attempt to correlate the South-Devon rocks with 
others of Archean age, I could only say that they cannot, in my 
opinion, be referred to the earlier portion of it. In all Archean 
rocks which I have examined, where there is any thing like a full 
development, the rocks become, broadly speaking, more distinctly 
bedded, more variable in their mineral character, more markedly 
foliated as weascend. ‘The threefold division mentioned above (I do 
not say that further subdivision is not possible) is very recognizable 
in the Alps; and this—into the group of granitoid gneisses, the group 
of more fissile gneisses and strong schists, and the group of variable 
well-bedded schists— suffices for my present purpose. The rocks of 
South Devon remind me most of members of the last group. I can- 
not find an exact parallel to them elsewhere in England; but so far 
as lithological evidence (and we have no other obtainable) avails us, 
I should consider them to belong to this third group, to be not very 
far away in geological position from the schists of the Lizard, but, 
if any thing, a little more recent. 
The above conclusions, if established, suggest one or two infe- 
rences of a more general nature. One as regards the physical history 
of a large adjacent area of country. I have indicated the successive 
changes which the rocks of South Devon have probably undergone. 
The great period of disturbance—the formation of the boundary 
fault, followed by the folding and the various results of lateral com- 
pression, including, in all, a long series of events—was doubtless 
subsequent to the deposition of the Carboniferous series as a whole. 
The flexures &c. of South Devon form parts of the great series of 
flexures, affecting all rocks, belonging and prior to that age, which 
can be traced from Belgium to the South of Ireland. It would seem 
to have been a wrinkling of the earth’s crust, scarcely less important 
than that to which the existing Alpine chain isdue. We can hardly 
help associating with its phenomena the great granitic intrusions 
and the other igneous masses of Cornwall and Devon, which fringe 
the north of the most highly compressed area, much as granitic and 
felsitic bosses now stud the southern margin of the Alps*. In short, 
* Tt may be worth noting the apparent absence of intrusive igneous rocks in 
the district described in this paper. There is a greenstone dyke near Torcross ; 
but I found no igneous rock in any other place to the south of it. Yet in the 
Lizard district, where the beds are less sharply folded and there is less evidence 
