540 
SILURIAN AND CARBONACEOUS SYSTEMS. 
shale, which, when in a more solid form, 
generally exhibit cleavage oblique to the 
stratification. 
5. The Silurian system resting con- 
formably on the preceding, and of great 
thickness, on the north-western coast, 
containing many subordinate beds and 
masses of limestone. In its range to- 
wards the eastern part of the county it 
gradually thins off, but its characters are 
well preserved, and it everywhere con- 
tains vast numbers of characteristic 
organic remains. 
6. The carbonaceous system of De- 
vonshire, in a direction east and west 
across the county, in its southern 
boundary so close to Dartmoor that its 
lower beds have been tilted up and al- 
tered by the granite. It occupies a 
trough, the northern border of which 
rests, partly in a conformable position 
upon the Silurian system, and partly 
upon older rocks, probably of the division 
No. 4. Its southern border also rests 
on the slate rocks of Launceston. It 
everywhere exhibits a succession of 
violent contortions. In some places it 
is overlaid by patches of green sand, and 
west of Bideford by conglomerates of 
the new red sandstone. The lowest 
portion of this vast deposit is generally 
thin bedded, sometimes composed of 
sandstone and shale, with impression of 
plants, sometimes of indurated compact 
slate, containing wavellite. These beds 
are surmounted by alternations of shale 
and dark-coloured limestone with a few 
fossils. Subordinate to these, there are 
on the western side of the county thin 
veins and flakes of culm or anthracite ; 
but this is wanting on the eastern side, 
and the calcareous beds are more ex- 
pended. The higher beds of this depo- 
sit are well exhibited on the coast west 
of Bideford. These often contain im- 
pressions of vegetables. Though in a 
state of greater induration than the or- 
dinary coal-measures of England, and 
even in many places destitute of of any 
trace of coal, still these beds do not 
differ from the great unproductive coal- 
field of Pembrokeshire. They conse- 
quently concluded, that from the order 
of superposition. — from mineral struc- 
ture — from absence of slaty cleavage 
peculiar to the older rocks on which 
this deposit rests, and from the specific 
character of its organic remains, it may 
without hesitation be referred to to the 
regular carboniferous series. 
In the course of the details, the 
authors alluded to a remarkable elevated 
beach, occupying two miles of coast on 
the north side of Barnstaple Bay, a 
more special account of which is being 
prepared for the Geological Society. 
Mr. De la Beche objected to the con- 
clusions of Messrs. Sedgwick and mur- 
chison, although he did not dispute the 
correctness of the section of the country 
which they had exhibited to the meeting. 
He conceived that he had traced the 
carbonaceous rocks passing into what 
had been termed the Cambrian sys 
tern, although he was not prepared 
to say that it really was that sys- 
tem. He was also unable to make that 
separation of the contorted rock, sug- 
gested by the authors of the paper. He 
spoke of the overlying greenstones in 
different places, and considered that 
those were of different ages ; also of the 
changes produced by granite on rocks of 
every kind in contact with it. He allud- 
ed to the former opinions of the rocks 
called by the general name, Greywacke, 
which opinions have, of late years, been 
totally altered. He attached very little 
importance to mineral characters ; un- 
less the consideration of the imbedded 
organic remains was made of the first 
importance, we were sure of falling into 
error. Are the organic remains in these 
carbonaceous rocks of Devon really the 
same as those of the general carbonifer- 
ous system ? He stated, that he con- 
ceived there was evidence to prove that 
there was a regular band of rocks sur- 
rounding Dartmoor, which had been 
thrust up through the hollow in the 
middle. He could nowhere discover any 
line of separation between the carbona- 
ceous and the older rocks, so that he 
was unable to reconcile the deposits of 
coal with those of other parts of Eng- 
land, and with the age of these older 
rocks all were agreed. In the Alps, or- 
ganic remains of the coal formation are 
found in beds, alternating with oolites, 
so that we must not limit too strickly 
the range of these organic remains as 
we should be certain of all the conditions 
under which coal plants can be accumu 
lated. We should recollect, that the re- 
mains of the vegetation of a mountain 
may be entombed at its base, so as to be 
shifted from its original habitat ; and 
that, although the disposition of organic 
remains may hold true for a certain ex- 
tent of the earth’s surface, we have no 
