Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/202

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Mr. Webster on the Strata lying over the Chalk.

Turning round this promontory, the lower chalk and chalk marl are seen at the bottom of the cliff and rising to the north-east, where they soon take place of the chalk, forming a mouldering slope at South Sea houses; they there give place to the green sand, which continues some way, then dips, and is covered by a flat beach extending many miles along Pevensey bay. It is almost needless to observe that the cliffs from Rottendean to Beachy head are oblique vertical sections of the South Downs, and have been formed by the action of the sea.

On entering the London basin at the south side from the sea, after passing the chalk cliffs at North Foreland and Margate, the blue clay makes its first appearance at Reculver; and at Swale cliff and Whitstable it is again seen.

But the Isle of Sheppey, consisting entirely of this stratum, and whose lofty cliffs on the north side furnish very extensive sections, affords the best opportunity for studying it.

Of this island, the northern half consists of a range of hills, of above 200 feet in height. These are cut down vertically by the action of the sea, which occasions the cliffs continually to fall: whole acres of land sometimes coming down at once; in consequence of which, the island must in a course even of a few centuries

    presence of mind to escape over the rent that was forming at some distance from the edge of the cliff. In a few seconds, the mass of chalk which he had stood on, to the extent of 300 feet in length, and 70 or 80 in breadth, fell with a tremendous crash. In going from Newhaven round Beachy Head, under the cliff at low water, I passed over these ruins, which were truly terrific, and observed that their fall had been occasioned by the sea acting on the chalk marl, and thus undermining the chalk; the former from the dip of the strata, just begins to appear at the bottom of the cliff at this spot. It may be proper to mention that this place is highly deserving to he visited, on account of the fossils to be seen in the chalk and green sand; among these I remarked many large madrepores, and some very large and entire shells of the fibrous kind, the fragments of which are so numerous in the chalk.