562 Geological Society. 
new, comprehensive name for this group, and thereby to prevent the 
confusion which had so long prevailed by the use of the words “‘Trans- 
ition” and “Grauwacke.” He adopted the term Silurian System, be- 
cause the territory in which the successive formations above mentioned 
are exhibited, was formerly occupied by the ancient, British people the 
Silures. The Silurian rocks are underlaid by vast masses which rise 
up into the mountains of North, and the western part of South Wales, 
and to these Professor Sedgwick, connecting his labours with those 
of Mr. Murchison, has assigned the name of ‘‘ Cambrian System.” 
A portion of last summer was employed in tracing these rocks from 
Caermarthenshire into Pembroke, and in doing this the author was 
Jed to attempt a general survey of the county, examining the strata 
from the youngest to the oldest, dwelling, however, specially on the 
deposits of the “ Silurian System.” 
Owing to its peninsulated form and the transverse fissures proceed- 
ing from Milford Haven into the heart of the county, Pembrokeshire 
affords great facilities for the comprehension of its mineral structure, 
and as the chief masses range from E. to W., sections from S. to N. 
expose the formations of which it is composed in descending order 
from the coal-measures to the Cambrian System. The points of 
novelty in the descriptions of the author apply to the persistence of 
the carboniferous deposits along the coast of St. Bride’s Bay, where 
they are not separated by any mass of greywacke as indicated in 
former maps, the parts producing culm*, lying simply to the N. 
and S. of a highly dislocated promontory of carboniferous grit. 
The contortions and innumerable faults of these coal-measures being 
pointed out, attention is then called to some of the probable results 
of such movements in the singular accumulations of finely fractured 
stone coal in small basins called ‘slashes,’ and to other vertical 
downcasts of the mineral termed “sloughs.” The shale of these culm 
deposits resembling in some respects certain strata of the upper Si- 
lurian rocks, might to an unpractised eye appear undistinguishable ; 
but even where the order of superposition is’not to be detected, essential 
differences are invariably to be observed, in the coal shales never con- 
taining those organic animal remains which are so abundant in the 
Silurian system, whilst the latter never contains a single plant simi- 
lar to those which abound in the former. Instances are cited where 
by dislocations the coal measures are thrown into positions apparently 
conformable to old greywacke rocks of the Cambrian system, and 
hence the author surmises, that if the millstone grit and carboniferous 
limestone were not present in many adjoining parts to test the true 
age of these coal measures, mistakes might easily result from such 
juxta-positions. Cherty and siliceous sandstones (the millstone grit) 
rise in dome shapes to the west of Haverford, and occupy large por- 
tions of the coal tract underlying the productive culm measures and 
capping the mountain limestone. 
Carboniferous Limestone.—In this formation, besides the very ac- 
* All the coal of Pembroke is stone coal, and it is usually in the laminated 
condition of culm, 
