Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/347

 a. Beds of light-coloured sometimes pinkish sand, in places interlaminated with bands of clay. They contain much carbonaceous matter, seams of lignite and nodules of pyrites about 30 ft.

b. Beds of grey and whitish laminated clay (with much lignite in places) and bands of nodular ironstone. These ironstones contain casts of shells, very imperfectly preserved, including Ostrea, Cardium, Corbula, and (Cerithium. I regard these as the equivalent of the " oyster-beds of Punfield." 30 to 40 ft.

c. Thin well-marked band of ironstone, very hard and dark- coloured, only a few inches thick. This bed is in places crowded with vegetable markings, and contains casts of marine shells. This bed rests directly upon the variegated beds of the Wealden, and seems to represent the " marine band of Punfield."

3. Mewps Bay. At this place, which, is 1-1/2 mile W. of Worborrow Bay, the very diminished representative of the Upper Neocomian (" Lower Greensand ") is faulted against the variegated beds of the Wealden. The same is the case in Bacon Hole a little farther west.

4. Lulworth Cove. This section is about one mile west of the former. On the eastern side we find lying directly upon the variegated beds grey clays with ferruginous bands containing much wood and vegetable matter, and also a few casts of shells, none of which are determinable. There appears to be here no trace of the Upper Neocomian (Lower Greensand), which is probably either quite overlapped by the overlying Cretaceous beds, or has altogether thinned out.

IV. Sections in the Isle of Wight.

The nearest Isle-of- Wight section of the Wealden strata, that of Compton Bay, is situated thirty miles due east of Punfield Cove. As, however, the clearest exhibition of the representatives of the Punfield formation is that in Brixton Bay, a little to the west of Atherfield Point, I propose in the first place to describe this in some detail, and then to point out in what respects the sections of Compton Bay and Sandown Bay differ from it.

Considerable diversity of opinion has existed among geologists with regard to the correlation of the Wealden beds of the Isle-of- Wight with those of the Weald-area of Kent, Surrey and Sussex. While Dr. Fitton * regards the upper grey shales and limestones as representative of the Weald Clay, and the sands and variegated beds below, as equivalent to the Hastings Sand, Mr. Bristow† considers the whole of the Isle-of- Wight series referable to the former subdivision, and believes that the latter is not represented in the island. The manner in which the Wealden beds thin out rapidly, or change their mineral character laterally within short distances, will always render any attempt at correlating their sub-


 * Trans. Geol. Soc. Ser. 2, vol. iv. p. 184, et seq.

† Memoirs of the Geological Survey, Geology of the Isle of Wight (1862), p. 8.