22 GENERAL HISTORICAL SUMMARY. 



ceding was a wetter one. In the second place, Norway has been elevated 

 since the glacial period, and the greater depth of peat-beds at high altitudes 

 is taken as an indication that the formation of peat began long before the land 

 reached its present level. 



The four layers of peat investigated by Steenstrup in Denmark are separated 

 by forest layers which agree with those of Norway. The profile for the two 

 countries is as follows: 



1. The present. The moors are mostly dry and contain a new root layer 

 ready to be buried under peat deposits as soon as the new moist period begins. 



2. Peat. Probable period of the invasion of sub- Atlantic flora, apparently 

 prehistoric, because stone implements are found in the young layers. 



3. Stumps with forest remains. 



4. Peat with trunks and leaves of Quercus sessiliflora. 



5. Stumps with forest remains, hazel, oak, etc. 



6. Peat with pine trunks. 



7. Stumps and forest remains. 



8. Peat with leaves of Popidus tremula and Betvla odorata. 



9. Clay with arctic plants, Dryas octopetala, Salix reticulata, Betvla 

 nana, etc. 



10. Closing stages of the glacial period; moist climate. 



Blytt's theory has been the storm center of the study of Scandinavian and 

 Danish moors. It has been accepted and modified by Sernander (1891, 1894, 

 1895, 1899, etc.), and vigorously combated by Andersson (1893, 1896, 1898, 

 1903, etc.). Blytt (1892) found further support for his view in an investiga- 

 tion of the calcareous tufas of Norway. Johanson (1888), Hulth (1899), 

 Holmboe (1904), Lewis (1905-1911), Haglund (1909), Samuelson (1911), and 

 others have studied boreal moors with especial reference to the theory of 

 alternating wet and dry periods. A brief summary of the views maintained 

 in this field is found in Chapter XIII. 



Hult, 1885-1887. — To Hult belongs the great credit of being the first to 

 fully recognize the fimdamental importance of development in vegetation, 

 and to make a systematic study of a region upon this basis. He maintained 

 that the distribution of plant communities could be understood only by tracing 

 the development from the first sparse colonies upon bare soil or in water to 

 the now dominant formations. He also laid down some of the general prin- 

 ciples upon which the developmental study of vegetation must be based, and 

 was the first to grasp the significance of the climax. In his classic investiga- 

 tion of the vegetation of Blekinge in Finland (1885:161), Hult traced the 

 succession of each intermediate formation through its various stages to the 

 supposed climax. He found that grassland on poor soil became heath; on 

 rich soil, oak wood. The heath developed into forest, dominated by Betula 

 alone, or mixed with Picea, Pinus, or Quercus. Betula is displaced upon dry 

 sandy soil by Pinus, upon moist soil by Picea. The spruce forest reacts upon 

 the soil tQ such a way as to favor the invasion of Fagus, which eventually 

 replaces the spruce. The birch forest can also be replaced by oak forest, which 

 gradually develops into beechwood. Where the oak becomes dominant in 

 grassland or heath, it develops into a scrub, which appears to yield finally 

 to beech scrub. On dry banks, the scrub is replaced by birch, this by spruce, 



