276 Proceedings of Royal Society of Edinburgh. [june 20 , 
the Piacentian marls. These facts seem to me to demonstrate the 
synchronism of the alluvial continental deposits nearer the moun- 
tains with the marine beds of the Astian. 
Now since we find that the yellow marine sands of the Astian 
are represented along the foot-slopes of the Apennines by more or 
less extensive gravelly, conglomeratic, torrential accumulations, and 
since in the higher parts of Piedmont we encounter continental de- 
posits of undoubted Pliocenic age (which attain a thickness of even 
100 metres at a distance of more than 50 kilometres from the Mari- 
time Alps, and rest directly upon the marine Astian), it seems only 
reasonable to expect that similar continental accumulations ought to 
be met with occupying a like geological position at the foot of the 
Central Alps. Indeed, when we consider the more extensive drain- 
age area of this latter region, its larger valleys and more imposing 
water-flow, we can hardly doubt that more or less extensive alluvia, 
synchronous with the Villafranchian of Piedmont, must have been 
deposited during the second half of the Pliocene by the great rivers 
then descending to the Pliocene sea. And these alluvia would 
form irregular deltas, now and again anastomosing and dovetailing, 
and spreading out from the Alps towards the Apennines. That 
great alluvial accumulations do occur along the foot of the Central 
Alps is of course well known, and the only question therefore that 
remains for discussion is the classification and correlation of those 
deposits. Unfortunately, owing to the fact that the cuttings made 
by the river-courses in the plains of the Po are generally of incon- 
siderable depth, the whole thickness of the alluvia is not seen, and 
the determination of the deposits therefore is not an easy matter. 
As a rule, it is only the superficial Quaternary conglomerates that 
are exposed in sections. Por the same reasons which induce me to 
believe that along the base of the Alps in Italy very extensive 
Pliocenic alluvia exist, I am of opinion that a large proportion of 
the alluvial accumulations, more especially the conglomerates, which 
occupy a similar position at the northern foot of the Alps, ought to 
be assigned to the Pliocene rather than the Quaternary. 
But the second stage of the Pliocene period was characterised 
not only by the commencement of the elevation of the Alpine and 
Apennine regions, and by the accumulation of the marine and con- 
tinental deposits already referred to, but by the initiation of those 
