86 Geological Society of London. 
vided, comprised in it several formations of great thickness, ranging 
in age from the Cambrian system of Prof. Sedgwick up to the true 
carboniferous series inclusive. The first groups mentioned by them 
in ascending order are the Cambrian and Lower Silurian, which 
great mass contains many distinct courses of limestone ; and is sep- 
arable into several formations, distinguishable from each other by 
stratigraphical position and by lithological and zoological characters. 
There appears, however, to be a great hiatus in the succession of 
rocks in Devonshire, as compared to South Wales, there being no 
traces of the upper Silurian strata, nor of the old red sandstone, nor 
even of the mountain limestone in its ordinary aspect. On the con- 
trary, the next group met with in ascending order, is a culmiferous 
series, the base of which distinctly reposes upon the above mentioned 
ancient rocks. This culmiferous deposit, far from appearing as a 
mere band, or at detached points, occupies about one third of the 
large county of Devon, and a considerable adjacent part of Cornwall ; 
its southern boundary ranging from Exeter on the east, by Launces- 
ton, to St. Gennis in Conwall on the west; its northern frontier 
running by Barnstable and and South Moulton to near Wellington 
in Somersetshire. These culmiferous beds are shown to contain 
thick beds of limestone; entirely dissimilar in structure and fossil 
contents from any limestones of the underlying “ grauwacke,” in 
which they had previously been merged. The culm measures con- 
sist of grit, sandstone, shale and limestone; and these rocks, it is 
said, are never affected by a slaty cleavage like the lower Silurian 
and Cambrian rocks on which they rest. From this character, aS 
well as from their prevailing mineralogical structure and imbedde 
fossil plants, the authors regard the culmiferous formation of Devon 
as perfectly identical in age with other coal-fields, and as more par- 
ticularly analogous to the culm-bearing strata of Pembrokeshire; @ 
part of which also once passed for “ grauwacke,”’ but Mr. Murchison 
has recently shown that it belongs to the South Welsh coal-field, 
which is known by al] geologists to rest upon mountain limestone. 
Thus referred to the age of our ordinary coal, these strata of 
North Devon are further proved to lie in a great trough, their south- 
ern edges being turned up against the granite of Dartmoor, where 
they acquire, in contact with the granite, when traversed by elvan 
dykes, many characters of the metamorphic rocks, or those com- 
monly termed primary. The phenomena of interference and altera- 
tion at the junction are such as to give a comparatively modern date 
