ON LAKE BASINS. 
589 
It miglit be thought from these accounts that lakes were 
universal phenomena^ so numerous and varied are the localities 
I have had occasion to refer to. A little consideration will 
remind the reader that this is by no means the case. There 
are other districts equally extensive in which no sheet of fresh 
water worthy of the name is to be found. Thus throughout 
the greater 23art of South America the rivers carry off the 
waters that fall on the land without expanding into large sheets. 
In Australia there are hardly any lakes of importance^ ex- 
cept those pools that dry up in the summer. There are fe\v 
also in Northern Asia. Mountain lakes^ or lakes such as we 
are now considering^ are in fact very limited in range. 
They are numerous on the slopes of the Alps^ and they 
abound, though on a far smaller scale, in the northern 
part of the British Islands. They are well marked in New 
Zealand, and there are good grounds for believing that many 
of the North American groups belong to the same series. 
But these occupy in all an exceedingly small area of the total 
amount of land. In the northern hemisphere the area is 
limited to small parts of the two great mountain systems, the 
old or north and south range affecting the western lands only, 
and the modern or east and west rang-e affecting the whole 
mass of European, Asiatic, and North African land. The lakes 
connected with the elevation of the Andes are extremely few, 
though so remarkable for their elevation. 
The great discussion concerning lake basins has been raised 
by some of our geologists familiar with a few small districts, 
but having only ^Dartial or hearsay knowledge of many important 
groups. All, lorobably, among the English geologists, are 
tolerably well acquainted with the British lakes, and many of 
them have seen something of the typical Swiss and North 
Italian lakes. The general forms of these are instructive. 
They are represented in the accompanying plate, where the 
English and Scotch lakes, drawn on a scale of 200 miles to an 
inch, may be compared with the Italian lakes, and the Lake 
of Geneva, on a scale of twenty miles to an inch. The actual 
detailed conditions of the basins, and the nature of the evidence 
that each affords in favour of any particular theory, are matters 
that require prolonged and careful study on the spot. At the 
same time there is much to be done by rapid travel in these 
countries, for a mere glance by those familiar with the resnlts 
of aqueous, atmospheric, ice action elsewhere is highly sug- 
gestive, and sound observations may be made by those well 
accustomed to observe and compare. 
The lake basins of the monntains about which discussion 
has chiefly been taken, are those of Geneva, in Switzerland, of 
Como, Lugano, and Maggiore in North Italy, of Scotland and 
VOL. IV. ^^NO. XVII. 2 B 
