280 Proceedings of Royal Society of Edinburgh. [june 20 , 
which in many respects may be looked upon as a period of torrents 
and flooded rivers. Since the close of that period the rivers and 
streams have been engaged in cutting down through the glacial and 
fiuvio-glacial accumulations, so that in some places they have suc- 
ceeded in reaching the Pliocene, and even the Miocene deposits. 
This is especially the case in localities where a movement of up- 
heaval had been longest continued, or where it had been most 
pronounced. The erosive action of Post-glacial times having resulted 
in the formation of alluvial terraces in the valleys over many wide 
regions, we term this period the “ Terracian.” 
Having now sketched in outline the phenomena connected with 
the structure and origin of the great lake-basins of the Alps, I may 
sum up in a few words my general conclusions. I am of opinion, 
then, that these basins came into existence during that powerful 
upheaval which closed the Pliocene — that, in short, they are the 
direct result of that great movement. They owe their origin partly 
to fractures and foldings of the strata, partly to subsidences and 
elevation. They were preserved during the glacial period by the 
glaciers which occupied them, and were only modified to a slight 
degree by morainic obstructions, and by fluviatile and glacial erosion. 
The form and distribution of the Alpine lakes seem readily 
explained according to my views as follows : — 
1. Along the south-east margin of Lake Garda the strata present 
distinct folds, the axes of which run generally from west to east. 
In other words, the undulations and folds of the strata along the 
eastern side of the lake are approximately parallel to the plain of 
the Po. Further to the east their direction is mostly from north- 
west to south-east. The absence of great lake-basins in the Y enetian 
Alps is noteworthy, and may be accounted for in various ways. It 
is not unlikely, in the first place, that fractures and faults would 
tend to take place more in the direction of the folds than perpendi- 
cular to them ; again, during the last great upheaval, when new 
foldings took place, these would probably be formed parallel to the 
pre-existing ones, and only rarely perpendicular to them. Finally, 
the Venetian Alps, according to Taramelli, experienced a less degree 
of elevation in Post-pliocene times than the regions lying to the 
west. Such considerations should lessen our surprise, that no great 
lake-basins occur in the mountain-valleys east of Lake Garda. 
