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The detached hills in their neighbourhood are doubtless only the remnants of an oolitic covering which once completely enveloped them. A noteworthy feature of the Mendips, but one shared by other limestone formations, is the number of caverns and "swallet holes" with which they abound.
It was a rainy day, and we passed the recess indoors. I remained quiet, looking over my lesson. "The first period ends with the carboniferous system; the second includes the saliferous and magnesian systems; the third comprises the oolitic and chalk systems; the fourth " "How attentive some people are to their lessons," I heard Charlotte Alden say. Looking up, I saw her near me with Elmira Sawyer.
The surface rock is invariably an oolitic limestone, mixed with an imperfect freestone, and in some places exhibits fossil banks, which bear evident marks of being of a very recent formation.
To cite an example of high geological antiquity, M. Hebert has demonstrated that, during the Oolitic and Cretaceous periods, similar inequalities in the vertical movements of the earth's crust took place in Switzerland and France.
Upper oolitic formation, including what are called Kimmeridge clay and Portland oolite. In Yorkshire there is an additional group above the lias, and in Sutherlandshire there is another group above that again. There are no particular appearances of disturbance between the close of the new red sandstone and the beginning of the oolite system, as far as has been observed in England.
When we are contrasting the vertebrate contents of two sets of superimposed strata of the Cretaceous, Oolitic, or any other ancient formation in which the shells are identical in species, we ought never to lose sight of the possibility of their having been separated by such intervals or by two or three thousand centuries.
Here round the Roman Ratæ, the predecessor of our Leicester, settled a tribe known as the Middle-English, while a small body pushed further southwards, and under the name of "South-Engle" occupied the oolitic upland that forms our present Northamptonshire. But the mass of the invaders seem to have held to the line of the Trent and to have pushed westward to its head-waters.
The geological character of the country was exactly similar to that we had been in so long, entirely of fossil formation, with a calcareous oolitic limestone forming the upper crusts, and though this was occasionally concealed by sand on the surface, we always were stopped by it in digging; it was seemingly a very recent deposit, full of marine shells, in every stage of petrifaction.
At Predazzo, in the Tyrol, secondary strata, some of which are limestones of the Oolitic period, have been traversed and altered by Plutonic rocks, one portion of which is an augitic porphyry, which passes insensibly into granite. The limestone is changed into granular marble, with a band of serpentine at the junction.
Observations have already been made on the distinctness of the organic remains of the Oolitic and Cretaceous strata, and the proportion of species common to the different members of the Oolite. Between the Lower Oolite and the Lias there is a somewhat greater break, for out of 256 mollusca of the Upper Lias, thirty- seven species only pass up into the Inferior Oolite.
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