THE TERTIARY SYSTEM. 



741 



Miocene. Vienna, Bordeaux, Turin, &c., with 18 per cent, of recent species. 

 Eocene. Paris, London, Belgium, with 3^ per cent, of recent species. 

 The denominative term Pliocene is an anglicised compound of nteiuv, more, and 

 recent, denoting the greater preponderance among its fossils of recent species. Miocene 

 is composed of //e*wv, less, and /caivo?, indicating that a minority only of fossil shells 

 imbedded in formations of this period are of recent species. Eocene consists of %u$, the 

 dawn, united to /caoo?, expressing the very small proportion of living species found in 

 strata of this description, therefore regarded as furnishing the dawn of the existing day 

 with reference to the animate creation. These terms may be familiarly taken to signify 

 ancient tertiary, middle tertiary, and modern tertiary, two divisions being made of the 

 deposits denoted by the latter term, the one more modern than the other. 



1. Eocene period, the dawn of recent, or ancient tertiary era. The strata of this 

 division, with which we are principally acquainted, are in England and France, and form 

 the London, Hampshire, and Paris basins. The series of beds in these districts differ in 

 number, composition, and order of succession ; but so far agree in their general features, 

 and in their organic remains, as to evidence their aggregation during the same geological 

 epoch. It is common, in the present day, for rivers at no great distance from each other 

 to be depositing at the same time different materials, and for marine formations to be 

 proceeding together, of a varying character, at several points of the same gulf. 



The London basin, of which a section is given, is a series of marine deposits, which 



occupy an extensive hollow or 

 depression in the chalk. The 

 chalk appears surrounding the 

 basin in the hills of the North 

 Downs ; Wiltshire, Oxfordshire, 

 Berkshire, and Hertfordshire, on 

 the south, south-east, west, and 

 north-west ; the other directions 

 from the metropolis to the sea 

 being occupied by continuous 

 tertiary strata, and the channel 

 of the Thames. That the chalk actually underlies the basin is not a geological inference, 

 but a fact proved by the sinking of wells through the superjacent beds to it. Immediately 

 above the chalk we have the Plastic Clay formation, so called from the use made of that 

 material for pottery ; but it is merely a subordinate stratum, connected with extensive 

 depositions of sand and shingle. The tunnel under the Thames, from Rotherhithe to 

 Wapping, traverses this formation, and the main difficulties of its construction arose from 

 the loose sandy strata. The next member above this is the firm London clay, varying 

 considerably in thickness, but sometimes attaining that of five hundred feet, and present- 

 ino- various shades of colour. This is the general substratum of the metropolis and its 

 vicinity, occurring immediately beneath the surface soil. It has not hitherto presented the 

 remains of any terrestrial mammalia ; but a great number of marine shells occur in it, 

 and the skeletons of crocodiles and turtles have been met with in it, at Highgate and 

 Islington, a proof, as Mr. Conybeare remarks, that the shores of some dry land must have 

 existed at the period of its deposition, within a distance easily accessible, to which these 

 animals resorted, according to their present habits. Pieces, and even masses, of fossil 

 wood have also been often found, exhibiting the perforations, and even the casts of an 

 animal, allied to the teredo navalis, the ship-worm, or borer, which now infests the seas 

 surrounding the West Indian islands, and proves so destructive to our vessels. Mr. Lyell 

 thus speaks of one of these fragments : " It must have once been buoyant and floating 



3B 3 



LONDON BASIN. 



1. River Thames ; 2. Marine sands; 3. London clay; 4. Plastic clay and 

 sands ; 5. Chalk with flints ; 6. Green-sand and Gault-clay. 



