272 Proceedings of Royal Society of Edinburgh. [june 20 , 
study of those lakes, we must, in the first place, transport ourselves 
in imagination to that epoch of powerful earth-movement which, 
according to most geologists, closed the Miocene period in the 
Alpine lands, and gave to that mountain-region its last general up- 
heaval. It was during this epoch of powerful movement that, 
according to common belief, the Alps received their present oro- 
graphic features, while many geologists were of opinion that the 
formation of the great Alpine lake-basins ought to be assigned to 
the same epoch of disturbance. With this latter opinion I cannot 
agree. On the contrary, I have been led to conclude that the 
movement of upheaval which brought the succeeding Pliocene 
period to a close was of much greater extent than that which took 
place after Miocene times ; and therefore, so far as regards the 
question at present under review, viz., the origin of the Alpine 
lake-basins, the Post-pliocenic movement is much the most im- 
portant. 
Be this as it may, it is quite certain that with the close of 
Miocene times marine conditions entirely disappeared on the 
northern side of the Alps. After that date the only deposits laid 
down in that region are of fluvio-lacustrine, fluviatile, and glacial 
origin ; and as none of these contains fossils, they do not furnish us 
with a sufficiently exact basis for the study of the phenomena 
which have taken place at the foot of the mountain-region since 
Miocene times. By various geologists these unfossiliferous deposits, 
which are in general gravelly in character, have been assigned to the 
Messinian, to the Piacentian, and even to the Astian stage, and in 
large measure also to the Quaternary. It is probable that during 
each of these epochs some of the deposits in question were formed, 
but as the classification of the latter is still far from being estab- 
lished, it is better for our present purpose that we should confine 
our attention to the post-miocenic accumulations which occur on 
the south side of the Alps. These, unlike those of Switzerland, are 
mostly marine and fossiliferous, and therefore afford us a more 
secure basis for the study of the question at issue. 
In the valley of the Po the Messinian is well marked, especially 
at the foot of the Apennines, where it contains gypsum and marls 
(with Dreissena , Melania, Melanopsis, Neritina, Paludina , Ceri- 
thium ), arenaceous, and calcareous beds ; in other words, the Mes- 
