OF THE SOUTH DEVON COAST. 13 
I postpone the full consideration of the facts recorded in the 
above descriptions until [ have given the results of the microscopic 
examination of the rocks, merely remarking that the evidence 
obtained in the field leads us to the following conclusions :—(1) 
that the foliated and slaty series are quite distinct rocks, the one 
much older than the other, so that very possibly the foliation of 
the former was anterior to the deposition of the latter, and that 
their junction is a faulted one; (2) that both have subsequently 
been subjected to tremendous lateral pressure, which has bent them 
into huge folds, cleaving the newer and producing marked effects 
on the older rock. 
6. Microscopic structure of (A) the Foliated Series, (B) the Slaty 
Serves. 
(A.) Regarded lithologically, the foliated series may be divided 
into two groups, the mica-schists and the chloritic schists, of 
which the former are decidedly the more fissile, the latter being 
occasionally almost massive. Macroscopically the mica-schists do 
not materially differ; they are of a dull lead-colour, sometimes 
rather dark, but often relieved by minute spangles of silvery mica, 
sometimes distinctly laminated with quartz ; but not seldom the latter 
mineral is inconspicuous. The surface often weathers to a rusty 
brown. The rock, almost everywhere, appears to have been much 
squeezed after it had assumed its present mineral character. Some- 
times it has a peculiar slickensided look, as near the Start ; some- 
times the surface of the foliation-planes is traversed by minute 
wavelike wrinklings ; sometimes, as especially about the Bolt Head, 
it is so crumpled as to break up under the hammer into rude 
prisms with irregularly fluted sides. 
Microscopically examined, the differences are merely varietal, 
and so slight that one description will suffice for the predominant 
characters of the specimens which I selected for cutting. The 
chief constituents are quartz, mica, and a variable amount of a 
minute black mineral. 
Quartz.—This occurs in granules variable in size. These are some- 
times at least as old as the time when the foliation was produced ; 
at others they have a chalcedonic aspect, as if a secondary product, 
in interstices due to subsequent disturbance. Cavities, especially in 
the former, are rather numerous, but extremely minute, so as to 
require for examination a magnification of at least from 300 to 
400 diameters. Some are rounded in outline, some vermiform, 
a few are irregular, and may possibly be films of some micaceous 
minerals. Bubbles are extremely rare. Sometimes the cavity 
is slightly darkened as if by the internal deposit of a ferruginous 
coating. 
Mica.—Of this mineral there appear to be three varieties—(a) a 
colourless mineral in flakes rarely exceeding :01" in length, exhibi- 
ting with the polarizing apparatus a satiny chromatic polarization, 
