XXXV11. 



Eocene flora, and quite distinct from the one above and below. Owing to a modification 

 of climate, occasioned probably by an altered distribution of land, the temperature 

 diminished from the close of the Middle Eocene to the Miocene age, when the tropical 

 plants, which still exist in some parts of the world, migrated and obtained a survival. 

 The relative age of our Tertiary beds may be calculated by the proportion of northern 

 types they contain. It has been already shown that the two members of the Lower 

 Eocene, the Woolwich and Reading and the London clay beds, have two distinct faunas, 

 a northern and a southern, which have no connection with each other, Mr. Gardner 

 attributes the distinctness of the faunas of the successive Eocene deposits to the 

 intervention of an isthmus between two seas, a northern and a southern, which shifted 

 its position north or south without being broken through ; it stretched at one time 

 towards Denmark, and separated the waters of the two seas. The Mediterranean was 

 then much larger than it is now, reaching to India, which was then an island, and over 

 the north of Africa. The Hampshire basin was then a large river delta, which extended 

 over parts of France and Belgium ; the river flowed from the west and must have drained 

 a considerable continent. The materials conveyed by it were mainly felspathic and 

 quartsoze from the palaeozoic rocks, through which it passed ; there are no flints, for the 

 chalk had not then been upheaved. The northern sea at first only occupied a small 

 portion of the east side of the London basin, but during the deposition of the London 

 clay it occupied the whole of the Hampshire basin, and on no occasion had the southern 

 fauna access, although a high temperature prevailed capable of maintaining southern 

 types. During the Bracklesham period the London clay was covered over by the southern 

 sea ; both formations appear to have been deposited from opposite directions, one from 

 the east, the other from the west, for their masses assume greater proportions in their 

 easterly and westerly extensions. The succeeding Barton beds show an admixture of 

 northern and southern types, with a remarkable absence of any truly tropical forms. It 

 is curious the lower cretaceous beds of America, called the Dakota beds, supposed to 

 represent the period of gault and upper greensand, consist of brackish and freshwater 

 deposits, with leaves of the higher types of dicotyledons. The flora of these beds so much 

 resembles that of the Reading beds, it leads to the impression that England formed part 

 of a continent which extended to America, and which is now covered by the Atlantic. 

 The junction of the chalk with the Woolwich and Reading beds at Studland is hidden 

 under a quantity of rubble with fragments of a breccia flint from a ferruginous band 

 overlying the chalk, which is soft and marly about two feet from its base ; below this the 

 chalk with flints dips to the north. The mottled clays and pebble beds of the Woolwich 

 and Reading beds require little notice, as they hold a very subordinate place at the base 

 of the chalk range, which runs east and west. The pipeclays, which belong to the 

 London clay series, are of considerable importance on account of their economic value. 

 They are worked extensively at Corfe and Creech ; and are usually referred to the 

 kaolinazation of felspathic minerals. A theory has lately been put forth that they are 

 referable to the decomposition of chalk during subaerial denudation and a sifting of the 

 iron it contains by the action of peaty acids. They contains besides palms, proteace0e j 

 azaleas, figs, sycamores, tropical ferns, and Leptomeria, belonging to a group of jointed 

 leafless trees, which in their striated internodes and tooth ribbed sheaths have some 

 resemblance to equisetaceae ; in other respects are allied to Ephedra, which now grows in 

 Australia, New Caledonia, and the Indian Archipelago. The oak, fig, and spindle tree 

 are widely distributed throughout Europe, Asia, and North America. This grand deposit 

 has been entirely exhausted, and, alas, very few of its invaluable plants preserved. In 

 the early days of geology, when the records of the earth's history were unappreciated, 



