1887.] Professor Sacco on Origin of Great Alpine Lakes . 273 
sinian consists principally of marshy and lagoon formations, in 
strong contrast to the underlying Tortonian, which is chiefly of 
deep-sea origin. 
Along the foot of the Alps the Messinian is very poorly de- 
veloped, and has been little studied. In the Eastern Alps, how- 
ever, there occurs a certain old alluvial deposit, cemented into hard 
rock, and containing terrestrial and lacustrine fossils. It has been 
elevated and much disturbed, but here and there is seen to overlie 
the Tortonian, while elsewhere it lies abruptly against much older 
formations. This alluvium M. Taramelli is inclined to include in 
the Messinian ; while M. Kossi * has assigned to the same geological 
horizon the extensive marshy deposits of the province of Treviso. 
But if in Northern Italy so strong a contrast exists between the 
deposits of the Tortonian and Messinian epochs, while on the 
northern side of the Alps the Upper Miocene strata are poorly de- 
veloped, surely we must infer from this that a powerful movement 
of elevation affected the region of the Alps and Apennines in post- 
Tortonian times. Is it not evident that this upheaval finally 
banished the sea from the northern side of the Alps, where it had 
so long prevailed, while on the south side of the Alps it changed the 
large and deep Tortonian gulf of the valley of the Po into a region 
of lagoons, low lands, and marshes ? Is it not to this period that 
the existing orography of the Alps, at all events in its general out- 
lines, ought to be assigned ? 
To this movement of powerful and wide-spread elevation suc- 
ceeded another movement, also of great intensity, but in the 
opposite direction. Thus in the valley of the Po the marshy 
accumulations of the Messinian are overlaid directly by the deep- 
sea deposits of the Piacentian. No marine deposits of Pliocene age 
occur on the north side of the Alps, and Swiss geologists therefore 
do not admit that the subsidence referred to affected their country. 
For my part, I think it highly probable that the movement in 
question did affect the whole mountain-region, but with varying in- 
tensity. The absence of marine Pliocene on the north side of the 
Alps I would attribute to the relatively higher position of that 
region above the sea-level. In consequence of the upheaval of late 
* “Note illustrative alia carta geologica della Provincia di Treviso,’’ Boll. 
Soc. Geol. llal ., vol. iii. 1884. 
