Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/174

From Wikisource
Jump to navigation Jump to search
This page has been validated.
Mr. Webster on the Strata lying over the Chalk.

The stratum marked A, is chalk with flints,[1] which at the north side is in nearly vertical layers, the inclination becoming gradually less and less towards the south side, where they dip about 60°.

  1. is chalk without flints.
  2. chalk marl.
  3. calcareous sand-stone, with subordinate beds of limestone and chert.
  4. bluish-black marl.
  5. ferruginous sand and sand-stone, with potters' clay, slate clay, argillaceous limestone, wood-coal, &c. The part of this stratum in the middle ranges of hills inclines only a few degrees, extending to the south side of the island, where it is horizontal. It is to be remarked, that towards this side of the island there is a higher range of hills H, composed of horizontal strata which correspond exactly with a part of those of the highly inclined series of the middle range, not only in their nature, but in their order of superposition; thus irresistibly forcing upon us the conclusion, that they belonged to the same formation, and that they had probably at some period been continuous.

The strata G, to the north of these already mentioned, consist of a numerous alternating series in a vertical position, and are composed chiefly of sand and clay. These may be seen to great advantage in Alum bay, where they form cliffs about 200 feet in height.

The whole of the most northern part of the island, I, consists of nearly horizontal strata, which come up abruptly against those that are vertical, but are slightly curved at their junction with the latter. These, however, proved to be entirely different in their mineralogical characters and in the fossils which they contained, from the strata

  1. It was this chalk, together with the vertical strata of Alum bay, and the horizontal strata on each side, that were first observed and described by Sir H. Englefield.