Зображення сторінки
PDF
ePub

ADDITIONAL OBSERVATIONS.

305

ADDITIONAL

SUPPLEMENTARY CHAPTER.

OBSERVATIONS ON THE GEOLOGY OF THE

ISLES OF WIGHT AND PURBECK, WITH NOTICES OF THE
MOST REMARKABLE FOSSILS RECENTLY DISCOVERED.

INTRODUCTORY-CLASSIFICATION OF THE EOCENE STRATA-SECTION AT RYDE-FOSSIL MAMMOTH-TERTIARY FOSSILS-DICOTYLEDONOUS LEAVES-PALM-LEAF FROM WHITECLIFF BAY-EOCENE TURTLES-CROCODILES- SERPENTS-MAMMALIA-CRETACEOUS FORMATION-BELEMNITELLA-PTEROCERA FROM ATHERFIELDANCYLOCERAS-MOLLUSKITE AND PHOSPHATIC STRATA-WEALDEN FORMATION-FIR-CONES-ABIETITES DUNKERI-WEALDEN REPTILES-PURBECK STRATA-RETROSPECTIVE SUMMARY.

SEVERAL valuable communications relating to the geology and fossil remains of the district this volume is designed to illustrate have been published since the former edition in the " Quarterly Journal of the Geological Society of London;" a list of these memoirs is prefixed.

The most important are those on the "Greensand Formation, as exposed in the range of cliffs that extends along the southern coast from Sandown Bay to Compton Bay, by Dr. Fitton"; on the "Classification of the Tertiary Deposits, by Mr. Prestwich"; and on the "Fossil Remains of some new species and genera of Mammalia from the eocene strata of the Island, by Professor Owen." In the monographs on British fossils now in course of publication by the Palæontographical Society, there are likewise figures and descriptions of the remains of several species and genera of fossil turtles, crocodiles, and serpents, and of shells, from the tertiary strata of Hampshire and the Isle of Wight. my recent communications to the Royal Society on the

In

iguanodon, hylæosaurus, and other saurians from the Wealden, many of the illustrations are from fossils obtained from Sandown and Brixton bays.

In the following account of these and other additions to the geology and palæontology of the island, the most interesting facts and observations are concisely noticed.

"In

§ 1. CLASSIFICATION OF THE TERTIARY STRATA.—▲ review of the fossil remains and stratigraphical characters of the deposits comprised under the general term "London Clay," (see the tabular arrangement, p. 43,) has led Mr. Prestwich to modify his former classification of the eocene strata of England. The lowermost beds at Alum Bay, the mottled clays, &c., Mr. Prestwich now conceives are naturally separated from the London clay, strictly so called, by a basement line, which he thus describes : the fine section at Alum Bay there may be seen, at a distance of about ninety-four feet from the chalk, a layer, not a foot thick, of rather large rounded black flint-pebbles, imbedded in green or furruginous yellow sand and brown clay, which separates the mass of the London clay on the one side from that of the mottled clays on the other, and constitutes the base of the former. This pebble-band contains a few organic remains, of which the most common are the teeth of a species of Lamna (Shark), and the Ditrupa plana (see Pl. III. fig. 3): it lies upon a somewhat uneven and worn surface of the underlying stratum. Inconsiderable in thickness, this bed is, nevertheless, remarkable for the extent of its range, the uniformity of its lithological characters, and the permanence of its organic remains conditions of the more value from the position of this stratum between the two main members of the eocene series. It forms an excellent base-line, and its characters are so well marked, that it can be traced without much difficulty from the Isle of Wight to Woodbridge in Suffolk, a distance in a straight line of above 160 miles from south

[blocks in formation]

west to north-east. It constitutes a distinct horizon, separating the London clay formation, by a change both in the paleontological conditions and in the ancient physical geography of the district, from the older eocene deposits which intervene between it and the chalk; its mineral mass being composed of the debris of the latter, while its animal remains belong to the period of the former."

At Whitecliff Bay, (p. 91) this "basement-bed" consists of a layer of brown sandy clay, with tabular septaria, mixed with greensand, and passes down into a conglomerate of flint pebbles and rounded fragments of chalk, with masses of greensand, full of the shells of Ditrupa plana.*

The basement bed contains altogether, in the various known localities, thirty species of testacea,† of which eight or ten are probably undescribed. Panopœa intermedia, Rostellaria Sowerbyi, Cardium Plumsteadiense, and Calyptrea trochiformis, are persistent throughout. The Hampshire tertiary series is now arranged by Mr. Prestwich in the following order: 1. (lowermost) Mottled clays and sands; 2. London clay, including the basement bed and Bognor strata; 3. Bracklesham (and Bagshot) deposits; 4. Barton clays; 5. Fluvio-marine, and Freshwater series.‡ The following table shows the equivalents in the London and Paris districts :

[blocks in formation]

* For details, see "Quart. Geol. Journal," vol. vi. pp. 256, 274.

† Ibid. p. 278.

"Quart. Geological Journal," vol. iii., p. 400.

According to this arrangement, the bed of oysters (chiefly of one species, Ostrea bellovacina,) which occurs at Reading, at Headley in Surrey, and at Newhaven in Sussex, is below the basement-bed of the London clay. The Bromley oyster-bed, Mr. Prestwich thinks, may probably be on the same level. At Castle Hill, near Newhaven, the oyster-bed is immediately covered by the pebble-bed, and masses occur of a hard conglomerate, composed of oyster-shells and pebbles, like that of Bromley.*

§ 2. SECTION OF THE FRESHWATER STRATA NEAR RYDE. In 1847, Mr. Dashwood, the intelligent proprietor of the water-works in the valley at Dover, near Ryde, bored to the depth of about 140 feet in quest of water; the following strata were passed through:-1. Shore shingle and sand, 13 feet; 2. Blue clay, 5 feet; 3. Freshwater limestone, the bottom layer, blue rag, 14 feet; 4. Whitish loam, 3 feet; 5. Blue clay, with shells, 4 feet; 6. Indurated blue clay, 9 feet; 7. White sand, 5 feet; 8. Blue clay, with few shells, 16 feet; 9. Layer of soft sandstone, 1 foot; 10. Greenish and blue clay, with intermixture of sand, full of freshwater shells, like those at Headon Hill, 64 feet. No organic remains of interest were

obtained.

* The interesting outlier of eocene strata at Castle Hill, of which a sketch of the natural section, exposed in 1822, forms the frontispiece of my "Fossils of the South Downs," is rapidly wasting away, from the inroads of the sea on the chalk cliffs below. On a visit to the spot, after an interval of ten years, I found all the well-known sections were destroyed, and inconsiderable vertical breaks here and there, from recent slips, were the only spots in which the relative positions of any of the beds could be examined. The whole face of the hill towards the sea was in so fissured a state as to render much caution necessary in traversing it.

FOSSIL DICOTYLEDONOUS TREES.

309

§ 3. REMAINS OF ELEPHAS PRIMIGENIUS IN THE DRIFT. The only additions to the mammalian relics from the diluvial loam and gravel previously recorded, namely, of the horse, deer, ox, and reindeer, are the remains of teeth and tusks of the mammoth, or extinct elephant, found near Ryde, by Dr. Bell Salter.

§ 4. FOSSILS FROM THE TERTIARY STRATA.-Many new species and genera of shells, and a few small corals, have been obtained from the eocene deposits of the island and the neighbouring coast of Hampshire; but without extended descriptions and numerous figures, incompatible with the plan of this work, it would be useless to particularise them. Fortunately the British corals and shells are in the course of publication by able naturalists, in the monographs of the Palæontographical Society; and a still more desirable source of instruction is now within reach of the collector, namely a series of specimens of all the genera and most of the species of the Hants and Isle of Wight tertiary shells, labelled and arranged, and at very moderate prices, by the British Natural History Society, established and conducted by Edward Charlesworth, Esq., of the Scientific Institution of York.

The most interesting vegetable and reptilian and mammalian remains discovered since the former edition are noticed in the following pages.

§ 5. FOLIAGE OF DICOTYLEDONOUS TREES.-In a previous chapter, (ante, p. 122,) a short account is given of the occurrence of dicotyledonous leaves belonging to a few genera, in some thin layers of sandy clay in the cliffs a short distance west of Bournemouth, in Hampshire; but, inadvertently, no reference was made to the previous notice of this fact by the Rev. P. B. Brodie, in the Proceedings of the Geological Society.*

I have lately obtained some beautiful specimens col

*Vol. iii. p. 592.

« НазадПродовжити »