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The unconformability of the ochraceous clay and the underlying sandstones might lead to the idea that the two formations belong to distinct geological periods, and are not due to the same agency, acting at successive times. One feature, however, shows their close connection. The ochraceous clay exhibits a remarkable identity of configuration with the underlying sandstones.
Where the widest gaps appear in the sequence of the fossil forms, as between the Permian and Triassic rocks, or between the Cretaceous and Eocene, examples of such unconformability are very frequent.
Professor Ramsay has remarked that there is a stratigraphical break; for in Kent, Surrey, and Sussex, at those few points where there are exposures of junctions of the Gault and Neocomian, the surface of the latter has been much eroded or denuded, while to the westward of the great chalk escarpment the unconformability of the two groups is equally striking.
But while unconformability invariably bears testimony to a lapse of unrepresented time, the conformability of two sets of strata in contact by no means implies that the newer formation immediately succeeded the older one. It simply implies that the ancient rocks were subjected to no movements of such a nature as to tilt, bend, or break them before the more modern formation was superimposed.
Blocks of granite also abound, of a pinkish tinge; and these with metamorphic rocks, contorted, twisted, and thrown into every conceivable position, afford a picture of dislocation or unconformability which would gladden a geological lecturer's heart; but at high flood this rough channel is all smoothed over, and it then conforms well with the river below it, which is half a mile wide.
The readiest way, perhaps, of persuading the reader that we may dispense with great and sudden revolutions in the geological order of events is by showing him how a regular and uninterrupted series of changes in the animate and inanimate world must give rise to such breaks in the sequence, and such unconformability of stratified rocks, as are usually thought to imply convulsions and catastrophes.
We may naturally expect the other proofs of unconformability will hereafter be detected at more than one point in so vast a succession of strata.
At the base of the formation beneath the rock- salt occur the Lower Sandstones and Marl, called provincially in Cheshire "water-stones," which are largely quarried for building. They are often ripple- marked, and are impressed with numerous footprints of reptiles. The basement beds of the Keuper rest with a slight unconformability upon an eroded surface of the "Bunter" next to be described.
Superficial Signs of the same obliterated by Denudation. Great Faults the Result of repeated Movements. Arrangement and Direction of parallel Folds of Strata. Unconformability. Overlapping Strata. Hence it follows, that what is now dry land was once under water.
It would be easy to multiply instances of similar unconformability in formations of other ages; but a few more will suffice. The carboniferous rocks before alluded to as horizontal on the borders of Wales are vertical in the Mendip hills in Somersetshire, where the overlying beds of the New Red Sandstone are horizontal.
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