Eocene Areas of the North of Europe.—The strata next in order in the descending series are those which I term Eocene.

In the map (Fig. 164) the position of several Eocene areas in the north of Europe is pointed out. When this map was constructed I classed as the newer part of the Eocene those Tertiary strata which have been described in the last chapter as Lower Miocene, and to which M. Beyrich has given the name of Oligocene. None of these occur in the London Basin, and they occupy in that of Hampshire, as we have seen at [p. 244], too insignificant a superficial area to be noticed in a map on this scale. They fill a larger space in the Paris Basin between the Seine and the Loire, and constitute also part of the northern limits of the area of the Netherlands which are shaded in the map.

It is in the northern part of the Isle of Wight that we have the uppermost beds of the true Eocene best exhibited—namely, those which correspond in their fossils with the celebrated gypsum of the Paris basin before alluded to, p. 231 (see Table, p. 252). That gypsum has been selected by almost all Continental geologists as affording the best line of demarkation between the Middle and Lower Tertiary, or, in other words, between the Lower Miocene and Eocene formations.

In reference to the Table I may observe, that the correlation of the French and English subdivisions here laid down is often a matter of great doubt and difficulty, notwithstanding their geographical proximity. This arises from various circumstances, partly from the former prevalence of marine conditions in one basin simultaneously with fluviatile or lacustrine in the other, and sometimes from the existence of land in one area causing a break or absence of all records during a period when deposits may have been in progress in the other basin. As bearing on this subject, it may be stated that we have unquestionable evidence of oscillations of level shown by the superposition of salt or brackish-water strata to fluviatile beds; and those of deep-sea origin to strata formed in shallow water. Even if the upward and downward movements were uniform in amount and direction, which is very improbable, their effect in producing the conversion of sea into land or land into sea would be different, according to the previous shape and varying elevation of the land and bottom of the sea. Lastly, denudation, marine and subaërial, has frequently caused the absence of deposits in one basin of corresponding age to those in the other, and this destructive agency has been more than ordinarily effective on account of the loose and unconsolidated nature of the sands and clays.

TABLE OF ENGLISH AND FRENCH EOCENE STRATA.
UPPER EOCENE

English subdivisionsFrench equivalents
A.1. Bembridge series, Isle of Wight,p. 252.A.1. Gypseous series of Montmartre,[p. 270.]
A.2. Osborne or St. Helen’s series,Isle of Wight, [p. 255.]A.2 and 3. Calcaire siliceux, orTravertin Inférieur, [p. 273.]
A.3. Headon series, Isle of Wight, [p. 255.]
A.4. Barton series. Sands and claysof Barton Cliff, Hants, [p. 258.]A.4. Grès de Beauchamp, orSables Moyens, [p. 273.]
MIDDLE EOCENE
B.1. Bracklesham series, [p. 259.]B.1. Calcaire Grossier [p. 274]
B.2. Alum Bay and Bournemouth beds,[p. 259.]B.2. Wanting in France?
B.2. Wanting in England?B.2. Soissonnais Sands, or LitsCoquilliers, [p. 275]
LOWER EOCENE
C.1. London Clay, [p. 263.]C.1. Argile de Londres, Cassel, nearDunkirk.
C.2. Woolwich and Reading series, [p. 267.]C.2. Argile plastique and lignite, [p. 276]
C.3. Thanet sands, [p. 269.]C.3. Sables de Bracheux, [p. 276]

UPPER EOCENE, ENGLAND.

Bembridge Series, A.1.—These beds are about 120 feet thick, and, as stated in [p. 245,] lie immediately under the Hempstead beds, near Yarmouth, in the Isle of Wight, being conformable with those Lower Miocene strata. They consist of marls, clays, and limestones of fresh-water, brackish, and marine origin. Some of the most abundant shells, as Cyrena semistriata var., and Paludina lenta, [Fig. 163,] are common to this and to the overlying Hempstead series; but the majority of the species are distinct. The following are the subdivisions described by the late Professor Forbes:
a. Upper marls, distinguished by the abundance of Melania turritissima, Forbes ([Fig. 165]).
b. Lower marls, characterised by Cerithium mutabile, Cyrena pulchra, etc., and by the remains of Trionyx (see [Fig. 166]).
c. Green marls, often abounding in a peculiar species of oyster, and accompanied by Cerithium, Mytilus, Arca, nucula, etc.
d. Bembridge limestones, compact cream-coloured limestones alternating with shales and marls, in all of which land-shells are common, especially at Sconce, near Yarmouth, as described by Mr. F. Edwards. The Bulimus ellipticus, Fig. 167, and Helix occlusa, Fig. 168, are among its best known land-shells. Paludina orbicularis, Fig. 169, is also of frequent occurrence. One of the bands is filled with a little globular Paludina. Among the fresh-water pulmonifera, Lymnea longiscata (Fig. 171) and Planorbis discus (Fig. 170) are the most generally distributed: the latter represents or takes the place of the Planorbis euomphalus (see Fig. 175) of the more ancient Headon series. Chara tuberculata (Fig. 172) is the characteristic Bembridge gyrogonite or seed-vessel.