Yenetia during the Neogene. 307 



recently emerged. Among the various talus slopes which com- 

 posed the delta, there appeared here and there, in the midst of 

 a tropical ve£>-etation, lakes or ponds, in which lived Melanias, 

 Planorbis, Pisidium ; into which fell with the leaves and 

 branches of Cinnamomum and other trees destined to become 

 buried and to form beds of lignite, the shells of Helix and 

 Clausilia ; and where herds of Hjomoschus, Dinotherium, and 

 Mastodons came to water. 



The early drainage system. 



It is in these early rivers, accordingly, that the beginning of 

 the recent drainage system can probably be found, whose origin 

 has not been overlooked by the geologists of the region, par- 

 ticularly Mms. Taramelli, Rossi, Dal Piaz, etc. 



The lithologic nature of the pebbles forming the Pontian 

 conglomerates in the extra-alpine region of Yenetia varies 

 greatly from place to place, according to the nature of the rocks 

 outcropping in the corresponding river basins. Thus there 

 are conglomerates formed almost entirely of dolomite, and of 

 limestones with flints, oolites, and Hippurites in eastern Yene- 

 tia. In eastern Treviso they become polygenetic, and mixed 

 with these limestones are Triassic or Permian sands, red hme- 

 stones and even nummulitic limestones. They enclose mica 

 schists, gneiss, granites and quartz porphyries in western Tre- 

 viso, evidently connected with streams rising in the Yalsugana 

 and Cima d'Asta, where many of these crystalline rocks are 

 only exposed to-day. Definite traces of this early drainage sys- 

 tem can elsewhere be recognized in certain patches of a con- 

 glomei-ate with rounded pebbles which one meets here and 

 there in the interior of the region, in the mountain region of 

 Friuli, at an elevation of 1500-1600 meters above sea-level, 

 everywhere on the divide between the valley of upper Tag- 

 liamento, and the head of the valleys of the Meduna and the 

 Arzino. The study of the rocks which are found as pebbles 

 in the Pontian conglomerates permits us to make still other 

 deductions. The Mesozoic limestones (particularly the Turon- 

 ian and Senonian limestones with Rudistes) form, it will be 

 remembered, the periphery of the Alpine chain in this region, — 

 that is to say, the base of the intra alpine zone, — but they never 

 appear farther in the interior, where the Upper Cretaceous 

 (locally called Scaglia) is transgressive on Jurassic or Eocreta- 

 ceous limestones. The great frequency of pebbles of this 

 Rudistes limestone in the Pontian conglomerate of Friuli is a 

 further proof in support of the hypothesis just enunciated, of 

 the partial emersion of the intra-alpine zone before the end of 

 the Tortonian ; for it is only in the Tortonian that these peb- 

 bles begin to appear. On the other hand, it must be noted 

 that the marine Tortonian beds, lying conformably on the 



