Geology of England and Wales. 149 
altogether omitted; as they now stand in the text, we should 
apprehend that they would perplex the student. 
We now enter upon the third of the four subdivisions of the 
supermedial rocks, namely, the oolétic series; it is chiefly im- 
portant as the great repository of the principal architectural 
materials which the island affords, and may be generally de- 
scribed as consisting of a series of alternating oolitic limestones, 
of calcareo-siliceous sandstones, and of argillaceous and argillo- 
calcareous beds, repeated in the same order. Three of these 
systems appear to comprehend all the beds which intervene 
between the iron sand and the new red sandstone, and each 
system lies upon a thick argillo-caleareous formation, consti- 
tuting a well marked line of demarcation, the oolitic rocks of 
each system forming a distinct range of hills separated from 
those of the other systems by a broad argillaceous valley. In 
England, these formations occupy a zone having nearly thirty 
miles in average breadth, extending across the island from 
Yorkshire on the north-east, to Dorsetshire on the south-west; 
they are characterized by peculiar organic remains, among which 
we enumerate many extinct genera of oviparous quadrupeds, 
apparently inhabitants of salt-water only, various vertebral fishes, 
testacea of all descriptions, coralloid zoophytes, encrinites, &c. 
We give our authors great credit for the explicit, and yet con- 
densed, account which they have given of the three oolitic 
systems. It embraces a clear view of all that has been done by 
others, enlightened by much original matter, well arranged, 
and luminously digested. 
The whole of the oolitic series reposes upon argillaceous 
deposits, the uppermost of which are deep blue marl, with a 
few irregular beds of limestone, which increase in frequency as 
we descend, and present a series of thin stony beds separated 
by narrow argillaceous layers. These beds are known by the 
name of lias; they are argillo-calcareous, and the white va- 
rieties admit of polish, and may be used for lithographic en- 
graving, while the blue or grey lias contains oxide of iron, and 
forms, when calcined, a strong lime, distinguished by its pro- 
perty of setting under water. The lias is nearly destitute of 
mineral products, if we except iron pyrites, which by its decom- 
position, frequently produces an aluminous efflorescence, as in 
the alum shale of Whitby, and sometimes a spontaneous inflam- 
mation, as in the cliffs near Charmouth. Organic remains are 
here very abundant and interesting ; they embrace more vertebral 
animals than are found in any other formation; among them are 
two remarkably extinct genera of oviparous quadrupeds, the 
ichthyosaurus, and the plesiosawrus; the former has been de- 
scribed and figured by Sir Everard Home in the Philosophical 
Transactions, under the name of proteosaurus; they have both 
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