THE QUATERNARY PERIOD. 347 



the fact that the great majority of the living beings of this 

 period belong to the species characteristic of the " new " or 

 Recent period. 



The Recent deposits, though of the highest possible interest, 

 do not properly concern the palaeontologist strictly so-called, 

 but the zoologist, since they contain the remains of none but 

 existing animals. They are " Pre-historic," but they belong 

 entirely to the existing terrestrial order. The Post-Pliocene 

 deposits, on the other hand, contain the remains of various 

 extinct Mammals ; and though Man undoubtedly existed in, 

 at any rate, the later portion of this period, if not through- 

 out the whole of it, they properly form part of the domain of 

 the palaeontologist. 



The Post-Pliocene deposits are extremely varied, and very 

 widely distributed ; and owing to the mode of their occurrence, 

 the ordinary geological tests of age are in their case but very 

 partially available. The subject of the classification of these 

 deposits is therefore an extremely complicated one ; and as 

 regards the age of even some of the most important of them, 

 there still exists considerable difference of opinion. For our 

 present purpose, it will be convenient to adopt a classifica- 

 tion of the Post-Pliocene deposits founded on the relations 

 which they bear in time to the great " Ice-age " or " Glacial 

 period;" though it is not pretended that our present knowl- 

 edge is sufficient to render such a classification more than a 

 provisional one. 



In the early Tertiary period, as we have seen, the climate of 

 the northern hemisphere, as shown by the Eocene animals and 

 plants, was very much hotter than it is at present partaking, 

 indeed, of a sub-tropical character. In the Middle Tertiary or 

 Miocene period, the temperature, though not so high, was still 

 much warmer than that now enjoyed by the northern hemi- 

 sphere ; and we know that the plants of temperate regions at 

 this time flourished within the Arctic circle. In the later 

 Tertiary or Pliocene period, again, there is evidence that the 

 northern hemisphere underwent a further progressive diminu- 

 tion of temperature ; though the climate of Europe generally 

 seems at the close of the Tertiary period to have been if any- 

 thing warmer, or at any rate not colder, than it is at the present 

 day. With the commencement of the Quaternary period, 

 however, this diminution of temperature became more de- 

 cided ; and beginning with a temperate climate, we find the 

 greater portion of the northern hemisphere to become gradu- 



