78 THE EAETH. 



of seas. This is the last of the great convulsions which the 

 earth has undergone, for the tertiary strata which afterwards 

 began to be deposited rest in the hollows or basins (chiefly 

 -in the chalk) then left ; the alterations in and since these 

 deposits appear to consist chiefly of the upheaval of certain 

 localities, the depression of others, the evaporation of inland 

 lakes, and the wear and tear of the land from these causes, 

 which are still in continuous action (as from the washing down 

 of cliffs by the sea, and the formation of mud deposits at the 

 mouths of rivers), or the volcanic agencies which in some 

 places (as in Ireland) have cast up basalt over the chalk. 



The tertiary strata contain remains of most of the classes 

 of animals now in existence, but yet differing greatly in 

 species, and as the strata approach the surface those species 

 become more and more general; the plants also approach 

 more nearly to those of the present time, but still most 

 parts of Europe possessed a climate almost tropical. The 

 tertiary strata consist chiefly of marine and fresh water 

 deposits in the form of sands and clays, as the " London 

 clay," which extends under London, resting upon a basin of 

 chalk. The last deposits, forming the superficial layer of 

 earth, and the formation last deposited before the creation 

 of man, are called the Diluvium and Alluvium, and contain 

 numerous remains of mammalia, birds, reptiles, and fishes. 

 One of the most extraordinary animals of this period was the 

 Dinotherium, a sort of walrus, which is supposed to have been 

 the largest of quadrupeds, if indeed it was one (fig. 31). 

 The quadrupeds of this, the " Pliocene " formation, are thus 

 described by Professor Owen in his "History of British 

 Eossil Mammals." 



" At the period indicated by these superficial stratified and 

 unstratified deposits the Mastodon had probably disappeared 

 from England, but gigantic elephants (fig. 32), nearly twice 

 the bulk of the largest individuals that now exist in Ceylon 

 and Africa, roamed here in herds, if one may judge from the 

 abundance of their remains. Two-horned rhinoceros, of 

 at least two species, forced their way through the ancient 

 forests or wallowed in the swamps. The lakes and rivers 

 were tenanted by hippopotami, as bulky and with as for- 



