down, are deposited in the lower parts of their courses to such an ex- 
tent as to be for ever raising the river beds. Owing to this, the ri- 
vers often change their courses in the lowlands, various side streams 
striking off from the main currents and seeking the sea separately. 
Lakes there are many, the largest being the Thingvallavatn and 
Mypvatn in both of which fish (char and trout) is caught in consider- 
able quantities. Many other lakes are also full of fish. 
GEOLOGICAL FORMATION AND SOIL 
From a geological point of view Iceland is a very young country. 
It is built up of basalt during the latest periods of the world’s history, 
when a long succession of volcanic eruptions piled hundreds of basaltic 
layers one on top of the other, so that the aggregate thickness of the 
strata thus deposited measures about 1000 metres. 
Between the older (tertiary) basalt formations which are chiefly to 
be found in the western, northern, and eastern divisions of the country, 
there are very meagre intercalated layers of other materials; but in 
the midland districts and in the south, where volcanic eruptions were 
frequent during the last stages of the Glacial Period and later, there 
may be seen, besides the basaltic layers, clastic materials in great 
quantities, as tuffs, breccias and conglomerates, formed of volcanic 
ashes, pumice-stone, moraines, riverine deposits, and the debris born 
down by Jjskulhlaup (j6kull bursts). The surface of these districts has 
changed considerably since the Ice Age, for the species of rock, of 
which the strata are made up, are rather soft and have therefore been 
unable to withstand the erosive agencies of air and water, while 
new volcanic eruptions have spread sheets of lava over large parts 
of them. 
During the greatest development of the Glacial Period the entire 
land was glaciated, except a few peaks which, like nunataks, rose 
above the ice. It was a moving mass of ice, projecting into the sea 
on every side, scraping off all loose material and carrying it forward 
and deeply grooving the sheets of basalt as it advanced. The valleys 
and furrows already in the basalt were then broadened and deepened 
by the discharge of ice from the interior icefields. When the ice dis- 
appeared, terminal moraines were left where the edge of the glacier 
had stopped for a time, and these traces of the Glacial Period are 
still visible in the shape of kames and gravel ridges. 
Excepting the volcanic parts in the southern and midland districts, 
the surface features of the land have, on the whole. changed but little