1887.] Professor Sacco on Origin of Great Alpine Lakes. 281 
2. Upon the south-west margin of that lake the foldings of the 
strata run usually from south-west to north-east— a direction which 
coincides generally with that maintained by the anticlinal and 
synclinal axes of the Western Alps, and explains why the Central 
Alps advance so much further into the plain of the Po than the 
Eastern Alps. By this arrangement of the axes in the region under 
review, it is obvious that the folds of the strata are directed 
approximately perpendicular to the plain of the Po. Now, since 
the faults and foldings which followed the trend of the original 
undulations must have been both numerous and important ; and as 
the Post-pliocene elevatory movement which took place in the 
Alpine region to the west of Lake Garda was very powerful, it is 
only natural that great sub-Alpine basins should have been formed 
in that region, the general trend of these basins being perpendicular 
to the plain of the Po. 
3. In that region where the discordancy between the undulations 
of the Central Alps and those of the Venetian Alps is most marked, 
we ought to encounter the largest faults and most pronounced fold- 
ings of the strata. Now, it is just in that particular region where 
Lake Garda occurs — a lake which advances further than any of the 
other Alpine lakes into the plain of the Po, and which in places 
exceeds the great depth of 800 metres — so that its bottom is nearly 
800 metres below the level of the sea. 
4. The larger foldings which occur along the southern area of the 
Eastern Alps are directed, as I have said, parallel to the plain of 
the Po, thus differing notably from the Post-miocene and Post- 
pliocene undulations of the Central Alps. This direction of the 
folds of the Eastern Alps, taken in connection with the disposition 
of the Alpine chain in a strong curved line, seems sufficient to 
account for the absence of deep lacustrine basins at the foot of the 
Venetian Alps. 
5. The northern region of the central area of the chain (including 
a large portion of the German Alps and the eastern part of Switzer- 
land) having experienced conditions very similar to those which 
have affected the Alps of Lombardy — for, doubtless the powerful 
elevation that closed the Pliocene epoch influenced the whole area 
in question, — we there meet with deep lacustrine basins similar to 
those of Northern Italy. These basins we see extend in a direction 
