iQii.l STEVEXSON— FORMATION OF COAL BEDS. 611 



1. Arctic freshwater beds, containing Salix polaris. S. reticulata, Betula 

 nana. etc. A semi-continental climate. 



2. Sub-glacial stage, with Betula odovata, Popnlus tremula, Salix, etc. 

 The moors were wet, the climate humid ; equivalent to the Danish " birch 

 or aspen period." 



3. Sub-Arctic stage, drier, many bogs became dry and were overspread 

 by forest growth ; Scotch fir (Pimis sylvestris) makes its first appearance. 



4. Infra-boreal stage, climate again humid ; the flora of Denmark is 

 still of true northern type; Pinus sylvestris the common tree. 



5. Boreal stage, climate drier and forests overspread the bogs, forming 

 a root bed ; Corylus and oak abundant. 



6. Atlantic stage, climate mild and humid ; Quercus scssi flora abundant 

 in Denmark and southern Sweden ; this is the Danish " oak period." 



7. Sub-boreal stage, drier than the last : many peat bogs dried up and 

 became forested. 



8. Sub-Atlantic stage, bogs again wet and the youngest peat layer was 

 formed ; this is the Danish " beech or alder period." 



9. Present stage, the bogs are drying and are becoming forested. 



Stages I to 4 are wanting in the low level bogs of the Scandinavian 

 coast as that region was still submerged. 



The peat deposits of Sweden have been studied by H. and L. 

 von Post, /\ndersson, Sernander and others, and those of Finland 

 by Andersson. It suffices for the present to present only the salient 

 facts as recorded by L. von Post/-^ reference to the work of some 

 others being deferred to a later portion of this work. A'on Post's 

 studies were made in the province of Xarke, southern Sweden. His 

 grouping is essentially the same as that offered by Weber but he 

 gives details, necessary to the present discussion, not noted by other 

 students. He finds the following types of deposits : 



Limnische. I. i. Allochthonous mineral deposits made in open water: here 

 are clay, with diatoms, poor in plankton, and clay-gyttja, which is 

 clay with much plankton and diatoms. 2. Allochthonous organic sedi- 

 ments, including (a) plankton-gyttja, in open, comparatively deep 

 water, gray to green, more or less elastic, composed of plankton, algae 

 abounding; (b) detritus-gyttja, in comparatively shallow water, from 

 Potaniogeton and Nympha-a, red-brown to yellow-black, granular, 

 mostly plant debris with some plankton; (c) Schwemmtorf, composed 

 of plant detritus; (d) Ufertorf. like the last and formed very near 

 the line of low water. It contains lenses of Lake and of Swamp peat. 



^''' L. von Post, " Stratigraphische Studien iiber einige Torfmoore in 

 Narke," Geol. Forcn. Forhaudi, Bd. 31, 1909, pp. 633-640, 644. 647. 



209 



