906 THE EXTINCTION OF SPECIES. 



the plants which took possession of the ground whence glaciers and snow-fields 

 retreated after the gi'eat diluvial ice-age, it is not necessary to look so far afield. 

 We need only bear in mind that in the period preceding that in which the glaciers 

 attained their maximum size in the higher mountains of the Alps, a flora must have 

 existed there, and that this flora would have been forced down from the higher to 

 the lower parts of the mountains and into the sub-alpine regions by the climatic 

 vicissitudes which occasioned the glacial condition. In the Tertiary Period the 

 diminution of temperature accompanying an increase of elevation was doubtless not 

 materially diflferent from what it is at the present day. The general relief of the 

 Alps was the same in the Miocene pei-iod as it is now; also in the Eocene period, and 

 even in the more recent portions of the Cretaceous period the Alps were already a 

 considerable mountain region including probably some high peaks. The Limestone 

 Alps had their fjords, and the Central Alps were deeply cut into by cross valleys. 

 The vegetation clothing the lower slopes could not be the same as that of the higher 

 regions, but, as at the present day, there must have been several floras situated one 

 above the other. Glaciers must have existed in a latitude of from 46° to 48° at an 

 elevation of 3000 metres in the highest depressions in the mountains, and that at so 

 small a distance as 50 kilometres from the sea-coast, and subject to a yearly variation 

 in temperature of 8°-10° Centigrade; and even though woods of Laurels and Myrtles 

 flourished in the latter part of the Miocene period of South-eastern Europe on the 

 spurs of the Alps on the margin of the Wiener Becken, that does not exclude the 

 possibility of an Alpine flora having developed simultaneously on the snow moun- 

 tains of that neighbourhood, and on the Rax-alp and the Hochschwab (in the 

 mountains of Northern Styi-ia). The Carniola Sclineeberg to the north of the Gulf 

 of Fiume afibrds quite sufiicient proof that even a mountain of only 1800 metres 

 may harbour Laurels and Evergreen Oaks at its feet, whilst alpine vegetation 

 flourishes on its summits. 



The fossil remains of the Miocene flora that are known to us were all discovered 

 in lowland places, and they therefore only represent the plants belonging to gently 

 undulating ground or growing on quite low movmtains, and no inferences can be 

 drawn from them as to the nature of the vegetation of the higher regions. I think 

 that we may fairly deduce the conclusion that the majority of the alpine species 

 lived on the heights of the Alps as long ago as in the Miocene period, and that the 

 Alpine Flora though repeatedly forced down to lower levels, always returned again. 

 As a matter of course the composition of the Alpine Flora underwent many changes 

 in the process. The partial intermixture of species belonging to adjacent floras 

 with the alpine species, which must inevitably have taken place in the course of 

 these displacements, led to inter-crossing and consequently to the production of 

 new species, whereof a proportion were no doubt adapted to the altered climatic 

 conditions and capable of preserving their existence. On the other hand, many 

 of the species which already inhabited the Alps in the Miocene Period have died 

 out there or have only survived at isolated spots of limited area, as, for instance, 

 Wulfenia Carinthiaca (see p. 882) in Carinthia, and Rhizohotrya alpina on the 



