1864. | Geology and Paleontology. 331 
which it is hard to assign precisely the date in the series of geological 
events. On the one hand we have Buch, Hoffman, and Ball, fully 
persuaded that the same causes which elevated the Swiss mountains 
produced the depressions which separate them. They think that the 
elevation was accompanied by crevasses more or less profound, which 
have formed the valleys, and that in the interior there exist other 
cavities, the roofs of which will be subsequently broken in—the 
present lakes being the remains of such cavities or founderings which 
have not yet been filled up by the silt brought down by the rivers. 
On the other hand, the disciples of Buffon, Playfair, and the Werner 
school, attribute the valleys and water-basins to erosion, or the destruc- 
tive action of fluids in motion. The latter class, as we have already 
noticed, are split into two parties, and disagree as to the nature of the 
erosive medium—the one following their ancient masters, look to the 
currents of the sea, rivers, and torrents; the others, amongst whom are 
some of our own, and French and continental geologists, advocate the 
newer theory of their having been scooped out by the grinding action 
of massive glaciers. Each of these theories may be justified by par- 
ticular facts; and M. Desor, at least, adopts them both, and applies 
either one or the other, as circumstances demand, distinguishing the 
lakes as orographic, and lakes of erosion. The former may be further 
divided into three classes—the lakes in synclinal valleys, such as 
the lake of Bourget ; those in isoclinal, such as Brienz and Wallenstadt, 
and those in the transverse valleys or cluses, of which the lakes of 
Thoune and of Uri are examples. The lakes of the Alps, according 
to M. Desor, are chiefly orographic ; whilst those of Neuchatel, Bienne, 
Morat, Zurich, Constance, and others in Lower Switzerland, are lakes 
of erosion. The question of the epoch of their formation is, however, 
very much complicated when the strata around them are examined. 
All over Lower Switzerland and the Jura are spread the well-known 
“ Alpine blocks,” which by their mode of transport would necessarily 
have passed above the lakes in arriving at their actual sites from their 
original beds ; and we cannot conceive why, if a current brought them, 
it should not have filled their basins and made a great mound of débris 
at the débouchures of the Alpine valleys. This difficulty involving 
the impossibility of the suspension of such blocks in mid-air, or the 
unlikelihood of their sustention on the surface of water 1,000 feet 
above the valley below, has been one of the main causes of the readi- 
ness with which the hypothesis of the former greater extension of 
the glaciers has been received, for across the surfaces of the ice- 
filled depressions the Alpine blocks would have naturally travelled 
from the Alps to the Jura. This general body of ice, covering all the 
valleys and deep hollows, is certainly a cause of uncertainty as to the 
epoch of the formation of the lakes, for they may evidently be anterior 
to the glacial epoch, their basins during that era being filled with water 
or ice; or they may be posterior, although M. Studer is not disposed 
to admit a posterior origin, which appears too recent to reconcile with 
the evident connection of the basins and valleys with the orography of 
the country. 
Another difficulty occurs. For a long time there has been known 
