1886.] ON YARIATIONS OF CLIMATE IN THE COURSE OF TIME. 



7 



mates. During the Glacial Age these species grew in the plains 

 at lower latitudes, but as the climate became milder they receded 

 gradually to the Far North and the high mountains. In the 

 warm plains they had to give vvay to the new immigrants and 

 this is the reason of our discovering hyperborean plants on the 

 mountains of Europe. 



If now we were to apply this explanation to the scattered 

 •extension of the species in Norway, we must bear in mind, that the 

 distances here are smaller, although at times there are several 

 degrees of latitude between the places, where the same species 

 appear. We must, therefore, see if an acceptable explanation 

 of the Norwegian flora can be made by means of geology, and 

 if the same be supported by other circumstances. 



It is not long since, geologically speaking, that the Scandi- 

 navian peninsula was covered with an inland ice, stretching 

 right out to sea, above which only solitary moiintain tops rose, 

 like the „nunataks" in Greenland. It is evident that the majority 

 of the present flora could not then exist in Norway. But the 

 present flora is older than the Glacial Age, which is conclusively 

 proved by specimens from the same being found in coal strata, 

 older than that period. Thus, yew^ fir, and spruce, hazel, willow 

 etc. have been found in old peat bogs of England and Switzer- 

 land, for instance, which are covered by the bottom moraine of 

 the inland ice. The present Norwegian flora, therefore, must 

 have lived in other countries which were free from ice during 

 the Glacial Age and inimigrated to Nonvay as the climate be- 

 ■came milder and the ice receded. This is the reason of Scandi- 

 navia having no peculiarly characteristic species, because the 

 flora has immigrated from outside countries and the time is so 

 Short since it settled in the country, that it has not yet had 

 time to produce new species. 



If we m^j now apply the geological way of explanation to the 

 flora, we come to the conclusion that the immigration took place 

 during repeated changes in the climate. After several thousands 

 of years with a severer climate which favoured the immigration 

 and extension of northern and eastern species, other thousands 



