1887.] Professor Sacco on Origin of Great Alpine Lakes. 277 
glacial conditions which subsequently attained so great a develop- 
ment. Even at an earlier stage than this, namely, in the Astian 
epoch, the Alpine snow-fields and glaciers probably reached a not- 
able development, especially in the northern part of the chain, 
where the geographical and orographical conditions, together with 
distance from the sea, would necessarily exert an influence favour- 
able to glaciation. For these reasons, I incline to think that the 
first glacial epoch of Swiss geologists coincided generally with the 
closing stage of the Pliocene. If, as I believe, the first notable ex- 
tension of glaciers began in Astian times, then we should expect to 
encounter on the south side of the Alps very considerable alluvia of 
Pliocene age, extending outwards from the mountains far into the 
plains. And this is just what I do find. 
The actual cause of this former great extension of the Alpine 
glaciers I would assign to evaporation from a much wider water 
area than presently exists. Much of what is now dry land in 
Northern Italy was then submerged — the water being partly that 
of the sea, partly lacustrine. The vapour rising from these sub- 
merged areas, passing north over the Alps (which at that time were 
being powerfully upheaved), would be precipitated as snow, and so 
would eventually give rise to glaciers. It must be remembered that 
the extraordinary glacier-development in question has, in all proba- 
bility, not been the first to have taken place in the Alps. At 
various horizons in the Tertiary strata great erratic blocks have been 
met with. More especially is this the case with the Miocene of the 
hills near Turin, where, scattered through sandy, marly strata of 
marine origin, occur enormous blocks, angular in shape, which could 
only have been carried by ice. It seems most likely that the ice- 
bergs or ice-rafts by which they travelled were detached from the 
front of the glaciers descending from the Alps into the sea of 
Miocene times. 
But if the movement of elevation began to be manifested more 
or less pronouncedly during the Astian epoch, it was yet gradual 
enough to allow of the continued accumulation of the deltas, which, 
step by step, were compelled to recede from the foot of the Alps. 
At the end of the Pliocene period, however, the movement assumed 
extraordinary intensit} 7- . Thus, the lower Pliocene (Piacentian) of 
deep-sea origin were uplifted 350 or 400 metres, and even more 
