IB 



A. BLYTT. 



[No. 8. 



plants and animals, the formation of the terraces the shellbanks 

 and the shore-lines, the rows in which the moraines appear, 

 and, finally, the alternation of the peat-layers and various geolo- 

 gical strata. It remains now only to find a natural cause of 

 such a periodical variation of the climate; but before doing this 

 it is necessary clearly to understand what the theory demands. 



It does not require great chcmges, all the facts on which it 

 is founded may be explained by comparatively small variations 

 in the extremes of temperature and rainfall. No very great 

 variation is required in order that the holly and similar coast 

 plants should be able to grow by the Christianiafjord, as the 

 theory assumes they once did. Because the holly, which cannot 

 stand the winter-cold at Christiania (lat 60 " N.), has for many 

 years been succesfully cultivated in open air at Horten, only 

 half a degree further south, on the same fjord. And along the 

 coast, plants of oriental origin have during the last thousands 

 of years spread from the Christiania and Throndhjems fjord right 

 out to the open shores of Jæderen and Fosen, the former in 

 lat. 58, 59 ^ and the latter in 63, 64 ^ N., and there would hardly 

 be required a very great change to enable them to grow also 

 in the interveuing district of the province of Bergen, which 

 would again make their extension continuous. 



Whether the surface of a bog becomes covered with forest or 

 not, whether the peat grows or not, whether during the rising the 

 erosion is strong enough to hollow out the shore-line, or the 

 carrying power of the river is great enough to the formation of 

 terraces, whether the edge of the inland-ice recedes or advances, 

 whether a deposit of clay or marl is to be formed in a certain 

 place near the shore, or whether clialk only is to be left — may 

 entirely depend on small variations in the climate, as the con- 

 ditions will alter as soon as a certain point is reached. The 

 periodical changes, dealt with here were, therefore, not great; 

 but as they acted simultaneously, and in the same direction, 

 over whole climatic areas, it must be generally-acting forces 

 which caused the same and not variations in local conditions. 



The theory advanced hel-e proves thus that the climate is 



