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WAT ORE 
[Fuly 8, 1886 
fore, must have lived in other countries which were free 
from ice during the Glacial Age,and immigrated to Norway 
as the climate became milder and the ice receded. This 
is the reason of Scandinavia having no peculiarly charac- 
teristic species, because the flora hasimmigrated from out- 
_ Side countries, and the time ts so short since tt settledin the 
country that it has not yet had time to produce new species. 
If we may now apply the geological theory of explana- 
tion to the flora, we come to the conclusion that the im- 
migration took place during repeated changes in the 
climate. After several thousands of years with a severer 
climate which favoured the immigration and extension of 
northern and eastern species, other thousands of years 
followed with a milder climate. During this period 
fresh immigrants came from the south and south-west, 
compelling the older flora to retreat. In this manner the 
climate must have changed several times since the Glacial 
Age, and the distribution of the 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 extension of coast as 
well as inland plants. The sunny screes, the slate dis- 
tricts, and the moist coast tracts are asylums where the | 
different floras have found refuge. In the intermediary 
parts they have been dislodged by the newcomers. But 
certain species, being indifferent to the variations, ex- 
tended constantly, at the expense of others, axd this zs 
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-bogs and examine their structure. 
We shall, for comparison’s sake, also examine the Danish 
ones, which are weli known from the researches of Prof. 
Steenstrup. 
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. Under the present 
conditions the growth of the peat is arrested, at all events 
in dry places. But just below the lichen and heather- 
covered surface we find on boring a pure, unmixed white 
moss (Sphagnum). It is this moss in particular which 
has formed 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 v a3 formed 
the bogs were woodless because they were too watery. 
We see, therefore, that the peat in these bogs has not 
grown very much within historical times, and that the 
layer of stumps of trees, which are found on the surface 
in the knolls, indicates an arrest of the growth of the 
peat, the duration of which may probably be measured 
by many hundreds, perhaps by thousands, of years. It 
might be argued that the present drier state of the bogs 
was simply due to the circumstance that the peat had 
grown so high that the moisture had run off. But this is 
not an acceptable explanation, because if we bore deeper 
in the peat we find that the oldest bogs are built of four 
layers of peat, and between these stand three layers of 
stumps, so that these bogs are for the fourth time covered 
with trees since they began to form. And as most of 
the bogs, if not all, are at present drier than they were 
before, the theory of merely local variations of the 
moisture is also insufficient to explain the phenomena. 
It remains, therefore, only to assume ¢hat periods of ary 
and wet have alternated during ages. The peat layers 
generally belong to the latter, and the stump layers speak 
of drier periods, when the bog was covered with trees. 
Of these four layers of peat, which in some places 
measure upwards of twenty-six feet in thickness, only the 
two youngest inclose, as far as the researches in Norway 
go to show, remains of foliferous trees sensitive to cold. 
And this justifies the assumption that they correspond to 
the four layers which Steenstrup has shown in the bogs 
of Denmark, and which appear like geological strata with 
distinct fossils, viz., the aspen, the fir, the oak, and the 
black alder. This comparison of the peat layers of 
Norway and Denmark is further supported by the cir- 
cumstance that layers of stumps are also found in the 
| Danish bogs, and here, too, they stand between the peat 
| layers of the various periods. They indicate long periods, 
during which also the Danish bogs were dry and partly 
covered with forests when the peat ceased to grow. But 
during these dry times the flora was changed through the 
immigration of new species, and when a wet time again 
set in, it was other trees which grew around the bogs, and 
which spread their boughs, leaves, and fruits over the 
watery bog, and the remains of which were buried by 
the growing layers of peat. 
In this manner the structure of the peat confirms the 
conclusion to which the distribution of the flora pointed, 
and if we take the fossil plants and marine shells to cur 
aid we may explain the gaps in the extension of the species 
without assuming long transports of seed. 
In the freshwater clay of Scania and Seeland, Prof. 
Nathorst has discovered numerous remnants of Arctic 
plants. This clay lies de/ow the peat. When it was 
deposited in the cavities of the old bottom moraines of 
the inland ice, not only the dwarf birch, but even hyper- 
borean plants, such as the Arctic Sadzx polaris and others, 
flourished in the southernmost parts of Scandinavia : 
| therefore the Arctic flora was the first which immigrated 
znto Scandinavia. It entered whilst the climate was very 
severe; but the climate became milder and more moist; the 
peat began to form ; then the aspen and birch entered, and, 
later on, under varying conditions of moisture, the fir and 
the spruce, with the flora of the mountains and forest glens, 
a series of species which have not yet been mentioned, viz. 
Mulgedium and Aconitum, many great ferns and grasses, 
wood-geraniums, and lychnis, &c. But the climate be- 
came warmer and warmer; and finally the foliferous 
trees, more sensitive to cold, entered, viz. the hazel, the 
lime, the ash, the oak, the maple, and a number of others 
from warmer regions. In the province of Bohus quanti- 
ties of stones of sweet cherries are found in many places, 
in peat, where this tree is now extinct ; and in the Nor- 
wegian peat-bogs hazel-nuts are very frequent in a certain 
layer, not only in the interior of the great coniferous 
forests, where not a single hazel-tree is found, but even in 
the heathery, woodless coast-lands. It will, theretore, be 
seen that the hazel and the sweet cherry were then very 
plentiful, and from this we may justly conclude that the 
trees, and shrubs, and herbs which thrive in their com- 
pany were also once far more plentiful than at present. 
Lt 7s this flora which has found an asylum in the above- 
mentioned screes. 
Following the period when Southern Norway was 
covered with foliferous forests to a far greater extent than 
now came a warm and moist one, in which the peat 
again began to grow. At that time the coast oak 
(Quercus sessiliflora) was_far more frequent than at 
present, judging by the evidence of the peat-bogs, and at 
that time, the shell deposits inform us (as shown by Prof. 
M. Sars), the present marine animals of the west coast were 
found in the Christiania fjord. And there 7s every reason to 
assume that the present flora of the west coast immigrated 
thither at that period from the south ef Sweden along the 
Christiania fjord to the west coast. 
New changes again set in, with new immigrants, and 
finally came the present age with its comparatively dry 
climate. But all these events are prehistoric, as is shown 
by the stone implements lying in the uppermost peat 
layer, close under the surface. 
PP DY ig aE aes 
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