610 STEVENSON— FORMATION OF COAL BEDS. [November 3, 



stunted and grew slowly amid unfavorable conditions, there being 

 70 annual rings to the inch ; yet the trees lived for several centuries. 

 In the larger swamps, two or even three layers of pine stumps are 

 found, in situ, with their bases and roots well-preserved. As the 

 surface became higher, and drier, the earlier mosses gave place to 

 others; SpJiaynnm appeared and, at length, heathers. The pines 

 yielded to the birches and those to alders, hazel bushes and Corylus. 

 This succession is found only in the central zone ; the deposit is too 

 thin on the border. 



Weber^-'^ after prolonged study of peat areas in northern Ger- 

 many, grouped the peat producing plants into ( i ) those which form 

 the moor; (2) those which grow on the peat; (3) those which love 

 peat or are bound to it. The best illustrations of the relations of 

 these groups are in moors which began in post-glacial time and have 

 continued until now. As the result of his examination, Weber suc- 

 ceeded in determining the stages in development of the bog and in 

 determining the part played by the several groups of plants. He 

 presented a classification which has been accepted by many of the 

 later students. This will be given in detail as applied to the Scandi- 

 navian deposits. 



Somewhat earlier, Blytt^-* had discovered that in western Nor- 

 way the typical succession is 



Feet. 



1. Sphagnous peat, about 5 



2. Forest bed, chiefly of Scotch fir. 



3. Peat more compressed than that of No. i, about 5 



4. Forest bed with oak stumps and myriads of hazel nuts. 



5. Glacial deposits. 



But in eastern Norway, there are four peat layers -alternating with 

 three forest beds. In Denmark he finds equally distinct evidence 

 for successive wet and dry periods. In summing up the conditions 

 observed in Norway, Sweden and Denmark, he finds record of the 

 following climatic changes : 



'"' C. A. Weber, " Aufbau und Vegetation der Moore Norddeutschlands," 

 En(iler. Bot. Jahrb., Vol. 40, 1908, Beibldf., No. 90, pp. 19-34. 

 '"* Blytt, cited by J. Geikie, " Great Ice Age," p. 495. 



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