THE PEAT CLISTASE. 379 



along with a dry heath flora. One forest generation could now succeed 

 another without leaving a trace, owing to complete decomposition in the air. 

 With another change bringing an increase of rainfall, the development of 

 moor would begin anew, and the trunks would become submerged in the peat. 



In connection with the above, Blytt distinguished the following periods : 



1. Last part of the glacial period. Moist climate. 



2. Arctic period = Dryas period of Nathorst. Clay with arctic plants. Conti- 



nental climate. 



3. Aspen period. Peat about 1 m. thick, with Popidus tremxda and Betvla odorata. 



Insular climate. 



4. Stumps and forest remains. Continental climate. 



5. Peat with trunks of Pinus silvestris and Stone Age implements. Insular climate. 



Subarctic period (including 3 and 4, which correspond with the pine period 

 of Nathorst). 



6. Stxmips and forest remains, especially hazel and oak. Boreal period. 



7. Peat with trunks of Quercus sessiliflora. Insular climate. Atlantic period, 



marked by the migration of the Atlantic flora. 



8. Stumps and forest remains. Continental climate. Subboreal period. 6 and 8 



correspond with Nathorst's oak period. 



9. Peat, consisting of Sphagnum. Moist climate, Subatlantic period. 



10. Present. Drying of most peat areas, resulting in the development of heath or 

 forest. 9 and 10 = alder-beech period. 



Fliche (1875) determined from the peat-bogs of France that Picea excelsa 

 was followed by PiniLS silvestris, together with species of Salix, Betula, Alnus, 

 Taxus, and Juniperus, and that these were succeeded by Quercus and Ulmus. 



Nathorst and Carlson (1885, 1886) have studied the fossils of calcareous tufa 

 in 42 localities in Sweden, and have reached the following conclusions: 



The presence of arctic-alpine species {Dryas, Salix herbacea) in three locali- 

 ties in Jemtland indicates that alpine plants once occurred at lower altitudes, 

 and explains the appearance of alpine species to-day below the high mountains. 

 These tufa deposits with alpine fossils were not formed during a purely arctic 

 climate, but at a time when the arctic vegetation was disappearing and the 

 pine invading. The occurrence of Hippophae inland at considerable eleve- 

 tions indicates that this coast species was originally alpine. The presence of 

 pine in most of the deposits and the absence of spruce must be taken to show 

 that the pine invaded Jemtland before the spruce, though the latter is now 

 dominant in many places. 



Johanson (1888) found that Swedish peat-moors show the same stump 

 layers which Blytt has discovered in those of Norway: 



In a moor in Smaland the author found three clear layers of pine stumps. 

 The bottom layer of the peat consisted of swamp-peat, Phragmites communis, 

 etc., at a depth of about 13 feet. At a depth of 8 to 10 feet appeared numerous 

 large stumps of Pinus silvestris, the majority of them stiU upright. Then 

 followed a layer of Sphagnum peat with Eriophorum vaginatum and CaUuna 

 vulgaris. At a depth of 5 to 6 feet, pine stumps were again found, and this 

 layer was separated by Sphagnum peat from the uppermost layer of pine 

 stumps, which was about 2 to 3 feet below the surface of the moor. Occa- 

 sionally oak stumps also appear in peat moors. 



Stump layers have a wide distribution in Swedish peat-moors, and indicate 

 that Sweden has undergone, since the glacial period, the same climatic changes 

 that Norway has. There are some peat moors in which no layers of stumps 



