DRAINING OF SWAMPS. 435 
those of Lombardy; she had, however, constructed smaller 
but more numerous lakes, which the improvidence of man has 
permitted to disappear. Auguste de Gasparin demonstrated 
more than thirty years ago that many natural dikes formerly 
existed in the mountain valleys, which have been swept away 
by the waters.” * 
Many Alpine valleys in Switzerland and Italy present un- 
questionable evidence of the former existence of chains of lakes 
in their basins, and this may be regarded as a general fact in 
regard to the primitive topography of mountainous regions. 
Where the forests have not been destroyed, the lakes remain 
as characteristic features of the geographical surface. Dut 
when the woods are felled, these reservoirs are sooner or later 
filled up by wash from the shores, and of course disappear. 
Geologists have calculated the period when the bottom of the 
Lake of Geneva will be levelled up and its outlet worn down. 
The Rhone will then flow, in an unbroken current, from its 
source in the great Rhone glacier to the Mediterranean Sea. 
Draining of Swamps. 
The reclamation of bogs and swamps by draining off the 
surface-water is doubtless much more ancient than the drain- 
ing of lakes. The beneficial results of the former mode of 
improvement are more unequivocal, and balanced by fewer 
disadvantages, and, at the same time, the processes by which it 
is effected are much simpler and more obvious. It has ac- 
cordingly been practised through the whole historical period, 
and in recent times operations for this purpose have assumed a 
magnitude, and been attended with economical as weil as 
sanitary and geographical effects, which entitle them to a high 
place in the efforts of man to ameliorate the natural conditions 
of the soil he occupies. 
The methods by which the draining of marshes is ordinarily 
accomplished are too familiar, and examples of their successful 
* Economie Rurale de la France, p. 289. 
