TRANSACTIONS OF SECTION E. 587 
or gulf towards the east. The denudation of this formation has been enormous 
along the base of the Alps, and only mere remnants are to be found. It is easily 
seen that their preservation is purely due to the accidental position in places where 
the great denuding force—viz., the advance of ice from the mountains—has been 
unable to touch them; in other instances the early deposition of moraine matter 
upon them has acted like a shield, and prevented their entire destruction, Such 
examples are well seen near Ivrea, in the well-known section in the gorge of the 
Chieusella near Stombinella, and in the moraine near San Giovanni. 
The scattered remnants of the pliocene formation south of the Alps, which took 
perhaps thousands of years to lay down, show well how soon a great formation, 
together with the preserved remains of the fauna living at the time, may be 
completely destroyed by subsequent denuding forces. Similar destruction must have 
occurred over and over again in past geological ages, and shows clearly how the 
scanty, broken record can be accounted for. 
It is an established fact that the great valleys of the Alps and Himalayas existed 
much in their present form during miocene times, and they may owe their exca- 
vation partly to the glacial action of that period, when these mountain slopes rose 
from the plain or margin of the ancient sea, far in front of the present line of slope, 
and were far higher than now. This idea particularly strikes one when looking 
at the ice ground spurs that run out into the plain south of the Lago d’Orta. The 
general and local elevation and depression that took place in post-miocene times 
seem quite sufficient to account for the difference in the comparative levels of 
adjacent transverse valleys, or an elevation along the base of the chain, clearly 
indicated at Orta by the northerly dip of the marine beds. It is reasonable to 
suppose that these movements were exerted in different degrees, at points all along 
this face of the Alps and within the same, and that the depression on the west has 
been less than on the east, so that the sea never extended far up the valley of Susa, 
and to a comparatively short distance up that of the Dora Baltea as compared with 
Maggiore, and the formation and excessive depth of this and similar lakes on the 
east is mainly due to this local depression and elevation. Depression has steadily 
continued in the delta of the Po, as in the Ganges at Calcutta; for, at Venice, borings 
showed depression of land surface to an extent of 400 feet, and they did not reach 
the base of the formation." 
It is not improbable that during the earlier extension of the glaciers into the 
Maggiore basin,” the sea still had access to it ;* this would have greatly aided in the 
remoyal of the marine deposits, and then the deeper erosion of its bed near the 
Borromean Islands, so well put forward by Sir Andrew Ramsay. "When we see 
the gigantic scouring which glaciers have effected in the hardest rocks on the sides 
and bottoms of valleys, when we lmow for certain the enormous thickness they 
reached in the Alps, I do not doubt for a moment their capability of deepening a 
rock basin very considerably, or their power to move forward over and against 
slopes so low as 2° to 3°.4 
The earliest extreme extension of the glaciers was very great ; we have evidence 
of it on the miocene hills near Turin, their surface being scattered over with trans- 
ported material of great size, quite unconnected with that other ancient period of 
glacial conditions during the miocene times mentioned above at a period too 
remote to further dwell upon here. Eyen now I feel that in dealing with this 
subject of the glaciation of the Alps, many of you may say that I am departing too 
much from geography. To this I would answer, glacial periods have been so inti- 
mately connected with the interchange of sea and land conditions, that where can 
1 Lyell, Prin. vol. i. p. 426. 
2 With reference to the moraines of Ivrea, see pamphlet by Luigi Bruno, 
LT terreni costituenti Vanfiteatro allu sbocco della Dora Baltea. 
3 The evidence is stronger as regards the Lago Garda. 
4 There appears to be too great an advocacy, on the one hand, of ice action 
having done all the work of denudation; while, on the other, some writers consider 
this to have been extremely limited ; it is the combination of the two forces, I think, 
that effects so much and in so different a manner and degree. 
