38 
SILTJRIA. 
[Chap. III. 
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lying associated Silurian strata, being con- 
formably underlain and overlain by dark grey 
schists. In fact, they constitute the natural 
base of the Llandeilo rocks (Lower and Upper) 
of the Shelve and Corndon district ; and they 
graduate upwards into these, dipping at high 
angles to the N.N.W., as represented in the 
previous general section, p. 26, and also in 
this diagram, taken from one of the published 
sections of the Government Survey. 
The dark schists, beneath the quartz-rocks, 
which I place in the same level as the Lingula- 
flags, have not as yet yielded fossils, and are 
obscured by intrusions of greenstone. 
In the peaks known as the Stiper Stones, 
the rock has all the appearance of having been 
altered by the influence of the heat which 
must have accompanied the evolution of those 
igneous rocks (chiefly greenstone) which occur 
on both sides of the ridge*. When most crys- 
talline, it is often intersected by veins of vi- 
treous quartz; and on the broken and weathered 
fragments are exposed numerous small white 
facets of quartz crystals, presenting a vivid 
contrast to the dull brown heath over which 
they are strewn. In the first of the accom- 
panying sketches f, in which the spectator is 
looking along the ridge to the S.S.W., the 
valley on the left hand has been excavated in 
the uppermost strata of the Longmynd rocks 
not far to the north of Linley. 
In the following sketch, on the contrary, 
the protruding rocks are the culminating por- 
tions of the rapid slope before adverted to, the 
strata of which form an integral part of the 
Lower Silurian Eocks. 
The altered condition of these rocks is again 
instructively exhibited at Granham, to the 
north of Yessons Coppice, near Pontesbury, 
where the chief mass is white and crystalline, 
much fissured, and penetrated by a vein charged 
* Several additional bosses of greenstone have been detected 
by Mr. Gibbs on the eastern side of the ridge ; and these I ex- 
amined when visiting this interesting tract in September 1856. 
T From a drawing by the Rev. J ohn Parker of Sweeny. 
