PL. IV


Turritella
Imbricataria
Nummulites
Lævigatus
Limnæa
Longiscata

Cardita Planicosta

(Fusus)
Leiostama Pyrus
Cyrena Semistriata

Planorbis Euomphalus

EOCENE AND OLIGOCENE

The Bracklesham Beds in Alum Bay (570 ft. thick) consist of clays, with lignite forming bands 6 in. to 2 ft. thick; white, yellow, and crimson sands; and in the upper part dark sandy clays, with bands showing impressions of marine fossils. Alum Bay takes its name from the alum formerly manufactured from the Tertiary clays. The coloured sands have made the bay famous. The colours of the sands when freshly exposed, and of the cliffs when wet with rain, are very rich and beautiful,—deep purple, crimson, yellow, white, and grey. Some of the beds are finely striped in different shades by current bedding. The contrast of these coloured cliffs with the White Chalk, weathered to a soft grey, of the other half of the bay is very striking and beautiful. About 45 ft. from the top is a conglomerate of flint pebbles, some of large size, cemented by iron oxide. In Whitecliff Bay the Bracklesham Beds (585 ft.) consist of clays, sands, and sandy clays, mostly dark, greenish and blue in colour, containing marine fossils and lignite. Sir Richard Worsley, in his History of the Isle of Wight, tells that in February, 1773, a bed of coal was laid bare in Whitecliff Bay, causing great excitement in the neighbourhood. People flocked to the shore for coal, but it proved worthless as fuel. It has, however, been worked to some extent in later years. In some of the beds are many fossils. Numbers have lately been visible where a large founder has taken place. There are large shells of Cardita planicosta and Turritella imbricataria. They are, however, very fragile. In a stratum just above these are numbers of a large Nummulite (Nummulites lævigatus). These are round flat shells like coins,—hence the name (Lat. nummus, a coin). They are a large species of foraminifera. We may split them with a penknife; and then we see a pretty spiral of tiny chambers. A smaller variety, N. variolarius, occurs a little further on, and a tiny kind, N. elegans, in the Barton clay. One of the most striking features of the later Eocene is the immense development of Nummulite limestones—vast beds built up of the delicate chambered shells of Nummulites,—which extend from the Alps and Carpathians into Thibet, and from Morocco, Algeria, and Egypt, through Afghanistan and the Himalaya to China. The pyramids of Egypt are built of this limestone.

The Bracklesham beds are followed by the Barton clay, famous for the number of beautiful fossil shells found at Barton on the Hampshire coast. At Whitecliff Bay the fossils are, unfortunately, very friable. At Alum Bay the pathway to the shore is in a gully in the upper part of the Barton clay. The strata consist of clays, sands, and sandy clays. The base of the beds is marked by the zone of Nummulites elegans. Numerous very pretty shells of the smaller Barton types may be found, with fragments of larger ones; or a whole one may be found. Owing to the cliff section cutting straight across the strata, which are nearly vertical, there is far less of the beds open to observation than at Barton, which probably accounts for the list of fossils being much smaller. The shells are chiefly several species of Pleurotoma, Rostellaria, Fusus, Voluta, Turritella, Natica, a small bivalve Corbula pisum, a tubular shell of a sand-boring mollusc Dentalium, Ostrœa, Pecten, Cardium, Crassatella. The fauna is like a blending of Malayan and New Zealand forms of marine life. Throughout the Eocene from the London clay onward the shells are such as abound in the warm sea south east of Asia. Similarly the plant remains take us into a tropic land, where fan palms and feather palms overshadowed the country, trees of the tropics mingling with trees we still find in more Northern latitudes. The general character of the flora as of the shells was Oriental and Malayan; both being succeeded in later strata by a flora and fauna with greater analogy to that now existing in Western North America.

In Alum Bay the Barton clay is suddenly succeeded by the very fine yellow and white sands which run along the western base of Headon Hill, the curve of the syncline bringing them round from a nearly vertical to an almost horizontal position. These are now known as the Barton Sand. They are 90 ft. thick, the whole of the Barton beds being 338 ft. in Alum Bay, 368 ft. in Whitecliff. The sands were formerly extensively used for glass making. They are almost unfossiliferous. The passage from Barton clay to the sands in Whitecliff Bay is more gradual. The sands here show some fine colouring which reminds us of the more celebrated sands of Alum Bay.

[11] See Memoir of Geological Survey of I. W. by H. J. Osborne White, F.G.S. 1921, p. 90.

Chapter IX

THE OLIGOCENE