8 



A. BL YTT. 



[No. 8. 



of years followed with a milder climate. DuriDg this period 

 fresh immigrants came from the south and south-west, compelling 

 the older flora to retreat, ln this manner the climate must have 

 changed several times since the Glacial Age and the distribution 

 of plants must have changed in accordance therewith. The 

 periods of variation are reflected in the present flora, and it 

 is the former which have led to the great gaps in the exten- 

 sion of coast as well as inland plants. The sunn}^ screes, the 

 slate districts, and the moist coast tracts are asylums where the 

 diff'erent floras have found refuges. In the intermediary parts 

 they have been dislodged b}^ the new comers. But certain spe- 

 cies being indifferent to the variations, extended constantly to 

 the expense of others, and this is the reason of the Norwegian 

 flora being so monotonous. 



In order to test the accuracy of this assertion we shall 

 first turn to the peat hogs and examine their structure. We 

 shall for comparisons sake also examine the Danish ones, which 

 are well known from the researches of Prof Steensti-up. 



In the forest and mountain districts of Norway there are 

 innumerable marshes. In the forest districts most of them are 

 now comparatively dry, the heather and wood covering parts of 

 the bog, and on the surface of the latter tiny mossy knolls are 

 often found in the middle of which stands the old stump of a 

 tree. An examination of the structure of the peat layers — 

 which is easily made with a bore — shows, that previous to the 

 present time, when the surface is generally more or less dry, 

 there was a period when the bog was much more watery. Un- 

 der the present conditions the growth of the peat is arrested, 

 at all events in dry places. But just below the lichen and 

 heathercovered surface we tind on boring a pure, unmixed white 

 moss (Sphagnum). It is this moss in particular which has for- 

 med the peat in the Norwegian bogs; and in the upper layers 

 — only one or two feet from the surface — flint implements 

 from the Stone Age are often found. At the period this upper 

 layer of Sphagnum was formed, the bogs were woodless, because 

 they were too watery. We see, therefore, that peat in these 



