GRAUWACKE SERIES.—SLATE ROCKS. 
33 
SLATE, 
in its varied appearances, occupies the generality 
of South Devon, southward of Dartmoor, being as it 
were diffused in all directions ; the other strata, 
lime, trapp, &c. being intruded between its courses 
and hills. Under the term slate, I here include every 
kind of rock popularly so called, andin consequence, 
for the sake of convenience confound together, rocks 
considered by some both “ primitive” and “ tran¬ 
sition.” However perfect, systems and tables as set 
forth in books may seem to be, and however desira¬ 
ble it might be, for me to present definite terms and 
divisions of the strata under examination, I am so 
clearly satisfied of the immatured condition of this 
science, simply from the fact, that local phenomena 
have not yet been narrowly investigated and com¬ 
pared, that I think it highly probable a few years 
will once more remodify existing opinions and 
classifications, and that, consequently, it can be no 
great outrage, to consider provisionally all our rocks 
of a slaty nature under one head, though, I do not 
mean to exclude conjecture and classification alto¬ 
gether. Thus, while under the term slate, I comprise 
mica-slate,* clay-slate, roofing slate, grey dunstone, 
greywacke-slate, flinty-slate, and greywacke, with 
perhaps some other minor kinds, I believe it would 
be unphilosophical, to disregard the principle of 
arrangement, derived from the occasional alternation* 
and intimate blendings of certain strata, together 
with the truly natural association of deposits, by 
the occurrence of the same description of animal 
remains and other structures in their substance. 
* 1 have endeavoured to justify myself in considering mica-slate 
as a portion of the general body of slate rock, altered in character 
by its connexion with granite ; but, I incline to think, that some 
kinds of mica-slate are indisputably of the same order as igneous 
strata. 
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