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46
I. PHYSICAL GEOGRAPHY.
vations regarding temperature began to be made in Sweden, but, until the middle
of the 19th century, the first-named observations are so unreliable or incomplete
that scarcely any deductions can be drawn from them.
A climatic question of the highest importance to Sweden and there examined
very carefully is that of the influence of the forests on its climate. This
influence is, according to Hamiierg, very slight, or even immaterial, as regards
temperature and humidity. As to rainfall, the forests are found to cause an
increase. It is, however, rather slight in most cases, and only on the coasts, with
a shoreward wind, does it amount much. But its real value is not yet known,
on account of the great difficulty in exactly measuring the quantity of moisture
and, especially, of snow which has fallen. According to Hamberg, the greater
part of the increase found is due to errors of observation, which tend always
to diminish the quantity measured, but more so on open plains and naked
mountains than on those covered with woods.
Regarding these matters, compare also the article Hydrography (p. 20).
4. GEOLOGY.1
Geologically speaking, Sweden is a country of very ancient origin and
consists to by far the largest extent of rocks whose formation dates
back to the earliest epochs of the world’s history. Futhermore, the main
mass of the land of Sweden has existed as a continent continuously
throughout the enormous periods of time that have elapsed since the
Swedish Silurian deposits, now only in part preserved, were first formed.
Exception must here be made respecting Skåne, the southernmost part of
the country, which was partially covered by the sea even during the Trias,
the Jurassic, and the Cretaceous Periods.
The above-mentioned characteristic of having formed a continental mass for
so vast a period of time, Sweden shares with Norway, Finland and the adjacent
parts of Russia, whereas most of the other European countries are covered by
more recent formations, several thousands of meters in thickness, which prove
those countries to have been covered by the sea during the greater part of the
time that Sweden has been solid land.
The following geological systems are found represented in
Sweden, each of them occupying approximately the area of the country
here assigned to it: Archaean 78 %; Pre-Cambrian Groups (Algonkian)
9-10 %; Silurian, unmetamorphosed 6-40 metamorphic 5-60 %; Trias
0-04 Rhæt-Lias 0-16 %; Cretaceous 0-70 %; also traces of the Tertiarj’
1 Of the maps illustrating this Article the one representing Sweden’s Rocks has been
reproduced, on a reduced scale, from the Geological General Map, scale 1: 1 500 000, published
by Tbe Geological Survey of Sweden (Sveriges geologiska undersökning), Series Ba, No. 6,
2nd Edn. 1910. — The map showing the conditions prevailing during the latter part of the
Glacial Period is based upon a map published by the same Institution, scale: 1:2 000000;
Series Ba, No. 5, 1898.
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