650 THE FRESH- WATER LOCHS OF SCOTLAND 
limnography in the near future, which will have an important 
influence on our conceptions as to the past history of the earth and 
its fauna and flora. 
In all, about 250 lakes have been referred to and briefly described. 
About 60 of these are situated in inland drainage areas, and the 
remaining 190 lakes are situated in the areas which drain directly to 
the ocean. The area covered by the 60 lakes of the inland drainage 
areas is just about the same as that of the 190 lakes draining 
directly to the ocean, namely 300,000 square English miles for each. 
This arises from the great size of the Caspian Sea, which is situated 
in the inland drainage area of the Eural-Asian continent. It is 
diflicult to estimate even approximately the area covered by all the 
lakes and rivers of the world, but it may be taken as not less than 
1 ,000,000 square English miles, or about of the land-surface. 
The most abundant development of lakes at the present time is 
found in those regions which have in recent geological times been 
covered by an ice-sheet. As examples may be cited the lakes 
situated towards the head-waters of the rivers St Lawrence, Churchill, 
Nelson, and Mississippi in America, and the Rhine, the Rhone, and 
the Po in Europe. On the other hand, some of the greatest river- 
basins in the world contain very few lakes, and none of great dimen- 
sions. The Amazon and the Orinoco in South America, the Indus 
and Ganges in Asia, the Niger and Orange Rivers in Africa, may be 
mentioned in this connection. In Eastern Africa there are numerous 
lakes towards the head-waters of the Congo, the Zambesi, and the 
Nile, and there is no evidence of glaciation in the region. Here the 
basins appear to have been formed by earth-warping and volcanic 
action in recent geological times. 
A detailed study of the phenomena now exhibited at the surface 
of the solid crust of the earth is the surest method of obtaining 
knowledge for the correct interpretation of the conditions under 
which the various geological formations of past ages were laid down. 
In the present state of our knowledge, five distinct regions appear to 
be indicated, each of which has its own individual characteristics, 
although it must be admitted that on the border-lines between these 
different areas the interpretation of the phenomena may be difficult 
and uncertain. 
1. The Region of Inland Drainage Areas. — This is estimated 
to cover 11,000,000 square English miles of the continents, or about 
20 per cent, of the land-surfaces and 5J per cent, of the whole 
surface of the globe. The rainfall is usually less than 10 inches 
per annum. The sand, gravel, and fine dust derived from the dis- 
integration of the rocks are distributed by winds and water in a 
manner not observed in other regions, and these fragments often 
