Indurated 
Shale and Gra- 
nular Lime- 
stone. 
180 Professor SeEpGWwick on the 
limestone separated by a thin bed of indurated shale, and the 
three beds are, for some distance, kept separate from each other 
by two wedges of trap, which are connected with, and undoubt- 
edly form a part of the superincumbent mass. I have endeavoured, 
by the accompanying .section (Pl. x. Fig. 2.) to convey a correct 
notion of this geological fact, which seems to prove the mecha- 
nical agency of the trap in a manner the most unequivocal and 
convincing. A good representation of the features of the place 
would require the pencil of a skilful artist. 
The upper bed of limestone, especially that part of it which 
protrudes into the trap, is white and perfectly granular. The 
indurated argillaceous bed is of a light grey colour, and 
when struck with the hammer, flies into sharp splinters or irre- 
gular angular fragments. The form of the fragments is partly 
due to a number of flaws or natural partings, coated over with 
minute crystalline plates, exactly like those observed by Professor 
Henslow in the hardened shale in contact with the Plas-Newydd 
dyke in the Isle of Anglesea*. The splinters are all translucent 
at the edges, and so hard that the knife makes very little im- 
pression upon them. They are nearly infusible, but very minute 
fragments, when urged to the utmost in the flame of the blow- 
pipe, exhibit a slight superficial glaze without melting down so 
as to lose their form. The lower part of the great bed of lime- 
stone, which forms the visible base of the escarpment, is less 
granular than the upper part, and is more discoloured by a number 
of cloudy blue spots. From analogy, I should conclude, that 
organic remains may be found in it; though I have not disco- 
vered any in the specimens brought away from this locality. It 
is not divided into subordinate beds by any natural partings, but 
may be regarded as one great mass of granular marble. All the 
* See the preceding Volume of the Society’s Transactions, p. 405. 
a 
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