Paleo-Geological and Geographical Maps of the British Islands. 285 
(1.) Eocene and Oligocene Strata.—These deposits occur chiefly in two separate 
tracts or “basins "—-that of London, and that of Hampshire and the Isle of Wight. 
They also occupy a large tract of the adjoining Continent. Originally these were 
connected in one great sheet ranging into the centre of France, and extending in 
England far beyond their present limits, both northwards and westwards, but how 
far it is extremely difficult, if not impossible, now to determine. Their disseverance 
into three separate tracts took place during the Miocene period ; when—by the 
contraction of the earth’s crust, the elevation of the ground now occupied by the 
Weald of Sussex into an anticlinal arch bordered by corresponding depressions, and 
the subsequent denudation of the strata—the London Tertiary basin was separated 
from that of Hampshire, and the Cretaceous strata, with the underlying Wealden 
beds, were brought to light.* At the same period, by denudation along the Straits of 
Dover, the Paris Tertiary basin was dissevered from that of London. This process 
of denudation has proceeded ever since, and has affected not only the Tertiary 
but the subordinate Secondary strata of the Cretaceous and Jurassic series: so 
that vast tracts of Chalk, Greensand, Oolite and Lias have been denuded away by 
atmospheric agencies from the commencement of the Miocene epoch downwards, and 
the boundary scarps have receded further and further in the direction of the dip of 
the strata to their present positions over the whole of the south of Europe, and 
the adjoining district of France and Belgium. 
During the formation of the Eocene and Oligocene beds, the north and west of 
the British Islands was, in all possibility, in the condition of dry land. It is 
probable that Ireland was joined to England and Scotland by a tract of Cretaceous 
rocks mantling round the hills of older formations. To the south of this tract of land 
the waters of the Tertiary sea spread, extending over the north and centre of France 
and Belgium, in which direction they become more limpid and free from sediment 
than during the epoch represented by the London clay, so that while beds of clay 
were being deposited over the area of the estuary of the Thames, others of pure 
limestone with nummulitest were being formed over the area of the Paris basin. 
Nature of the Hocene and Oligocene Strata.—The oldest beds consist of gravels, 
sands, and clays, of marine or fluvio-marine origin.[ These are succeeded 
by the London clay, a blue and brown stiff clay, with Sepiaria, about 500 feet 
in thickness, and of marine origin. This formation thins away in the direction 
of the Isle of Wight. The succeeding Middle Hocene beds consist of the Bagshot 
sands and Bracklesham beds, of estuarine origin, and the upper, of the Barton 
clay, of marine origin, 300 feet in thickness. The “ Oligocene beds ” of Beyrich 
* Ramsay: “Phys. Geol. and Geog. of Great Britain.” 
t In the lower part of the ‘‘Calcaire grossier” of Paris there are three species of Vummudites abundant, 
viz.: WV. levigata, N. scabra, N. Lamarki, which serve to show that it corresponds 1o the epoch of the 
formation of the great Nummulite limestone of the South of Europe, &c. One of these, V. levigata, 
occurs in the Middle Eocene beds of England. 
t The Thanet Sands and “ Woolwich and Reading Beds” of Prestwich. 
