438 PIIOCBEDINGS OP THE GEOLOGICAL SOCIETY. [JlUie 5, 



favourable conditions of existence in the seas which then covered 

 Lancashire. 3rdlj and lastly. On the land emerging from the sea, 

 the isolated glacier- areas show that the climate was severe, but yet 

 not so severe as in the time of the continuous ice-sheet. On the 

 Continent the traces of this lowering of the temperature are to be 

 found in the travelled blocks and the Boulder-clay, which occupy 

 the whole region north of the continuation of the line passing through 

 the Thames valley eastward into Russia. To the south, however, 

 of this line there is no evidence of a continuous ice-sheet — a fact 

 which can only be accounted for bj' the climate at the time having 

 been less severe than in the northern region. Nevertheless a mer 

 de glace extended far over the Jura from the lofty axis of the Alps ; 

 and glaciers have left their unmistakable moraines in the valley 

 of the E.hine, at least as far down as Suabia, as well as in Lombardy. 

 The Alps, indeed, formed an axis, from which the ice extended 

 far down on every side into the lower districts. M. Desor has 

 proved that the three climatal changes which are so marked are 

 traceable also in Switzerland. The lignite beds of Diirnten, which 

 have furnished the remains of Eleplias antiquus, rest on an ancient 

 moraine, and are also covered by a mass of glacial detritus. It is 

 clear, therefore, that before the accumulation of the lignite the cold 

 was suiRciently intense to allow of glaciers occupying the horizon, 

 that during the growth of the trees on the spot the glaciers had 

 retreated, and that subsequently there was a reversion to the in- 

 tense cold of the first Glacial period. These three changes have not 

 been traced in any other part of the Continent. 



The moraines and roches moutonnees and detritus which cover the 

 flanks of the Pyrenees prove that they formed an axis from which 

 the glaciers radiated into France and Spain. And similar remains 

 detected by M. Dclanoue in the valley of the Dordogne prove that 

 the higher region of Auvergnc was also covered with ice. 



The mere fact of these glaciated areas being isolated shows that 

 the Pleistocene climate was less severe in Central than in Northern 

 Europe, although the angular condition of the superficial detritus, 

 pointed out by Mr. Godwin- Austen, in the south of England, and the 

 twisted and contorted river-gravels of Britain and Northern France, 

 noted by Mr. Prestwich, that have been disturbed by the contact 

 of ice, imply a temperature considerably lower than that which is 

 now found in those countries. 



On physical grounds, therefore, we have reason to believe that in 

 the Pleistocene period, treated as a whole, there were two distinct cli- 

 matal zones — the arctic, which extended as far down as a line passing 

 through the vallejr of the Thames eastwards, and a zone with cold 

 winter and warm summer, which extended from this line as far south 

 as the Alps and Pyrenees. In the one the northern division of the 

 Pleistocene mammaha found their head quarters, while the other 

 afforded a common feeding-ground for both northern and southern 

 animals. And the northern boundary of the latter gradually passed 

 northwards, as the temperature became warmer, as far as the shores 

 of the Baltic, probably in the latest stage of the Pleistocene. 



