1861.] PISHER BEACKLESHABI BEDS. 91 



there are few to be met with, while the shells are much less broken. 

 This shows that the pebble-bed was a very local condition of the 

 sea-bottom of that period, either caused by the spot being subject to 

 stronger currents, or to its being a littoral zone. The matrix, how- 

 ever, in which the pebbles are imbedded is of a different character 

 from the bed beneath, being finer and more argillaceous. There 

 must, therefore, have been a change in the conditions of deposition 

 accompanying, or immediately succeeding, the dispersion of the 

 pebbles. And one new condition seems to have been, that the 

 amount of deposit for a long period of time was comparatively very 

 small, so that the exuviae of many generations of mollusks were ac- 

 cumulated in a small vertical range. Afterwards the amount of 

 deposit increased, , and simultaneously the Bracklesham tjrpes dis- 

 appeared from the locality. There is another pebble-bed at High 

 Cliff, lower in the series ; and a similar change in the deposit occurs 

 there also. Prom a sharp sand we pass upwards into a sandy clay, 

 and the pebbles are imbedded in the base of the bed of clay. 



In short, it appears as if a pebble-bed usually accompanied a 

 change from a shallow to a deeper condition of the sea. Can the 

 dispersion of these pebbles have been owing to sudden subsidence of 

 the sea-bottom ? This is a question which has much interest ; and, 

 when we consider the local condition of the area, it does not appear 

 to suggest an improbable solution of the phenomena. Such move- 

 ments would have distributed pebbles to a certain distance from 

 the marginal zone, or from such other accumulations as may have 

 been subject to their influence. 



Sir Charles Lyell has brought together proofs that the Weald had 

 begun to be elevated before the Eocene period*. The elevation of the 

 Chalk of the Isle of Wight is undoubtedly a part of the same 

 system of disturbances ; and the present contorted form which it 

 has assumed is merely an intensified condition of a form that it had 

 begun to assume before the Eocene period. AnticHnals were then 

 probably forming where anticlinals exist now ; and the synclinals 

 occupy the same positions that they did of old. 



Moreover the whole effect was produced by lateral pressure. 

 When, then, at any period the pressure had accumulated to such an 

 extent that the beds gave way, the anticlinals would be raised and 

 the synclinals be depressed relatively, if not absolutely ; and thus 

 (the curves occupying but moderate intervals) areas tiot far distant 

 would be raised and depressed simultaneously. Nor does it appear 

 necessary that an equal amount of disturbance should take place 

 along the axis of the country at the same period; but a portion 

 towards the east might be more affected at one time, and towards 

 the west at another. 



Movements are still going on in the island. Mr. Godwin- Austen, 

 amongst other evidences of change of level, refers to an old well, near 

 Brading, which is now -rendered useless, being covered by the sea 

 at high tidcf. The opposite coast of Sussex has been not unfre- 



* Manual of Geology, 5th ed. p. 282. 



t Quart. Joum. Gcol. Soc. vol, xiii, p. 66. 



