18 PROF. T. G. BONNEY ON THE GEOLOGY 
so as to exhibit a structure in one part of the slide which might 
readily be mistaken for false-bedding *. 
A specimen from the curiously corrugated rock at the headland 
north of the last locality (p. 4) shows a similar mineral structure, 
butonemore conspicuously banded, the slide having been very skilfully 
cut from the apex of a fold. In this, however, the micaceous 
constituent occurs in slightly larger flakes. Still, notwithstanding 
the presence of a hydrous mica, which perhaps we may venture 
to designate sericite, these rocks differ widely from the normal 
foliated rocks and, if we restrict the term schist to the latter, they 
have no claim to that title. These filmy minerals appear to be 
very readily formed under pressure from damp argillaceous material 
in a fine state of division, and rocks in which they occur alone differ 
widely under the microscope, and usually to the naked eye, from 
the true mica-schists. I call special attention to this because I 
have noticed in some authors a tendency to confuse these two 
generally well-defined and widely separated groups of rocks. 
A specimen from a rather gritty-looking band in the cliffs south 
of Torcross shows a minutely granular, somewhat streaky structure, 
and appears to consist of quartz, white mica, a dusty mineral, proba- 
bly kaolin, perhaps a little calcite, with ferrite, opacite, and a filmy 
mineral belonging to the chloritic group. Bands of secondary 
quartz associated with some of the last-named mineral traverse 
the slide. Another somewhat similar rock, in which scales of 
silvery mica are distinctly visible to the eye, from south of Bossons 
Sands, exhibits a coarser texture under the microscope, consisting 
chiefly of grains of quartz and flakes of white mica with streaky 
ferrite and opacite; the quartz is rather full of minute cavities, 
bubbles being very rare, if not absent. The rock has evidently been 
much compressed, and some slight amount of mineral change has 
taken place. I have little doubt that the more conspicuous quartz 
grains and mica flakes are derivative and indicate the destruction 
of a gneiss or mica-schist. 
Specimens of the greyish, greenish, and blackish rocks from near 
the fault in the Hope Cove have also been examined ; but a very 
minute description does not seem to me necessary. They are 
clearly not foliated rocks, though they have been much compressed, 
and consist of fine aluminous sediments of rather varied nature, 
associated with some quartz, calcite, and numerous microlithic 
minerals which it is hopeless to identify with precision. For my 
present purpose it suilices to say that I have no hesitation in 
classing these with the slaty group, not with the true schists of 
South Devon. 
7. Peculiaritees of Structure m the Slaty Serves. 
I have already called attention to the remarkable corrugations 
and schistose structure locally exhibited by members of the slaty 
* This structure is described by Prof. Lapworth; Geol. Mag., Dee. ii. 
vol, viii. p. 348. 
