312 G, Stefanhii — Geological History of Yenetia. 



depth toward the end of this substa^e ; it was slowly tilled up 

 with sediments in the middle Miocene, assuming at the end of 

 the Miocene a continental phase. Invaded in part once more 

 by the lower Pliocene, bearing a fauna of less tropical aspect, 

 the region emerged again and for the last time before the end 

 of this period. 



During this long time tectonic movements caused at least 

 four violent disturbances. The tirst took place in the middle 

 Oligocene, and was accompanied by the basaltic eruptions of 

 Yicenza. To these ancient movements is due the shape of the 

 Preadriatic gulf, which assumed its shape, we repeat, immedi- 

 ately after, — i. e., in the upper Oligocene. 



The successive tectonic movements were produced along the 

 same major lines, at the end of the middle Miocene, at the 

 beginning of the upper Pliocene, and in the middle Quater- 

 nary. With the second of these periods of uplift is correlated 

 the beginning, and with the last two a rejuvenation of the 

 drainage system, revealed by the nature of the sediments and 

 by very plain morphologic records. 



The existence of continental Quaternary terrains, and of the 

 underlying marine Pliocene buried under alluvium at an eleva- 

 tion considerably below the present sea-level in the plain of the 

 Po, is contirmed by every-day experience in the construction of 

 deep wells, proving that these last Pliocene and post-Pliocene 

 elevations have been probably accompanied or immediately fol- 

 lowed by sinking in the adjoining regions. 



I have already said that the same phenomenon occurred at 

 the beginning of the upper Tortonian — the intra-alpine zone 

 rose, the extra-alpine zone, that is to say the bottom of the gulf, 

 sank. 



In studying these movements from a still wider point of 

 view, I believe the conclusion can be drawn that, in all the 

 instances considered, the elevation of a zone, which may be 

 called a zone of erosion, is coincident w-ith the sinking of the 

 bottom in the corresponding basin of sedimentation. 



As to the direction of these different folds, it is evident that 

 they are always produced parallel to the shores as well as in the 

 direction of pre-existing folds. 



The Venetian Prealps are a result, then, of the juxtaposition 

 of folds more and more recent, as one passes from north to 

 south. 



This phenomenon, pushed to the extreme, particularly in the 

 eastern part of the region, will produce the complete dying out 

 of the alpine folds toward the plain, with the overturning and 

 stretching of the lower flank of some of them, pushed some- 

 times to the formation of true overthrust faults, which give a 

 very characteristic nature to the structure of the Prealpine 

 chain of Yenetia. 



