430 NATURAL SCIENCE. ^,^^3^. 



deposits of the Mediterranean, we may, therefore, consider that the 

 severity of the Glacial Epoch died out rapidly towards the south, a 

 refrigeration of 20° in Britain being represented by one of 5° only in 

 the South of Europe. 



Thus far we have dealt solely with the temperature of the sea. 

 We will now study the evidence as to the temperature of the air during 

 the same period, and here again we can employ both physical and 

 biological data. The evidence for the former existence in Northern 

 and Central Europe of vast sheets of ice, of greatly extended glaciers, 

 and of deeply frozen soil, is overwhelming, and is so familiar that it 

 need not again be discussed. All the country north of the Thames, 

 and north of a line drawn eastward through Saxony, was buried under 

 a perennial sheet of ice and snow. Near this limit, and apparently 

 advancing or retreating with the ice, stretched a belt of barren and 

 frozen land, with dwarf birch and willow and other arctic plants, 

 but without trees. In this belt flourished also a mammalian fauna 

 like that now inhabiting the Arctic Regions. 



Remains of this boreal fauna and flora have now been found so 

 abundantly, and the list includes so many species, that it would be 

 impossible in the limits of a short article to give more than one or 

 two examples. Taking the examples from what is now the warmest 

 part of our islands, we may instance the dwarf birch and the bear- 

 berry found in clays at Bovey Tracey, in Devonshire, though both 

 these species are arctic and alpine plants not now living in the South 

 of England. In several parts of Norfolk and Suffolk a still more 

 arctic flora is found, for it includes the Salix polaris, a plant now 

 extinct in Britain, even on the highest mountains. Arctic mammals, 

 also, must formerly have been abundant in the South of England, 

 for besides the lemmings and musk-ox of the Thames Valley, we 

 have at Fisherton, near Salisbury, quite an extensive arctic fauna. 



An arctic flora like that just described has lately been traced 

 through great part of Central and Northern Europe by Professor 

 Nathorst ; and the corresponding mammalian fauna, with the 

 interesting addition of certain species now inhabiting the cold deserts 

 of Central Asia, is gradually being brought to light, principally 

 through the exertions of Professor Nehring. 



To compare then with now, we must again go to high northern 

 regions, for it is only within the Arctic Circle that we can find 

 physical conditions, and a fauna and flora, like those which once 

 characterised our islands. Britain in those days was probably much 

 like the existing Greenland, though with important differences caused 

 by geographical conditions. After making every allowance for the 

 probable excessive snowfall in Western Europe, it seems impossible 

 to place the average temperature at the southern margin of the 

 ice-sheet higher than the freezing-point — that is to say, 20° lower 

 than at present. It must be remembered that we are dealing mainly 

 with a low flat country, not much above the sea-level, and distant 



