56 



years, and during which the formation of turf was arrested, to 

 be resumed again when a wet period supervened. Such inter- 

 rupted periods of dryness and wet he considers to be closely 

 related to the several long-interrupted glacial periods which, 

 according to Geikie, have succeeded one another. In accordance 

 with Herr Blytt's view, the close of the first glacial age was 

 followed by a dry period, in which an Arctic flora appeared in 

 Scandinavia, traces of which, as leaves of Dryas octopetala and 

 Salix reticulata ) have been found in the clay underlying the 

 bogs in Denmark and Southern Sweden, in the latter of which 

 the same flora is to be seen interposed between two ancient 

 moraines. The boreal flora, the author is of opinion, we may 

 refer to a dry period, characterised by great summer heat; and 

 in the deposits belonging to this age we find abundant remains 

 of such deciduous trees as the hazel and the Primus avium, 

 which are now of rare occurrence in Norway, while many other 

 vegetable forms represented in these beds have been long extinct. 

 The differences observable in the bogs of Denmark and Norway, 

 Herr Blytt refers to the fact that while the former has under- 

 gone very little if any elevation, the latter has risen since the 

 glacial age 600 feet above the level of the sea. In Norway the 

 formation of the turf-beds may be gauged by their varying 

 elevations. Thus in South-east Norway, where the old sea- 

 level has been raised to a height of 600 feet, the turf is from 20 

 to 26 feet deep, while at low levels, as 30 feet above the strand, 

 the bogs are seldom more than from two to four feet deep." 



In Sir Joseph Hooker's address to the Geographical Section 

 of the British Association, in i88i,f he thus resumes Professor 

 Blytt's facts respecting the stratification of the bogs : — 



" The proofs of the alternating wet and dry seasons rest on 

 the fact that the different layers of peat in each bog present 

 widely different characters, and these characters recur in the 

 same order in all the bogs. First, there is a layer of wet spongy 

 peat, with the remains of bog mosses and aquatic plants ; this 

 gradually passes upwards into a layer' of dry soil containing 

 the remains of many land plants and prostrate trunks of trees, 



f Reported in Nature, 8th September, 1881. 



