34 GEOLOGICAL MEMOIRS. 



the strata, which have been much upheaved in conformity with par- 

 allel fissures. 



Ill the centre of the region in question, the Dachstein-limestone is 

 overlaid by limestones having oolitic structure, and of greyish-yellow 

 or white colour. In the lower part of these limestones are beds of 

 marl, which, when softened by inordinate quantities of water, are the 

 causes of great earth-slips. The enormous blocks choking the Adige 

 Valley at Marco, south of Roveredo, have been thus brought down 

 the western slope of Monte Zeuoa. 



The rocks resting on the oolitic limestones are, first, red and grey 

 Ammonitic Jurassic limestone, then Biancone and Scaglia. The same 

 deposits appear regularly on the west banks of the Lake of Garda ; 

 but rest there on spotted marls or immediately on the Dachstein- 

 limestone. 



Eocene deposits are conspicuous near Torbole and Arco. Diluvial 

 gravel occurs in considerable quantities near Arco, Tenno, and Villa. 



Among the eruptive rocks, the syenites along the Sarca and Chiesa, 

 and the porphyries along the Adige, are particularly noticeable. 

 Melaphyres and basaltic rocks, although occurring in many localities 

 of the Adige Valley, have nowhere conspicuously acted on the adja- 

 cent deposits. 



The extended survey in Southern Tyrol, over the whole of the 

 region of the River Sarca (Roveredo, Trente, Val Sugana, Primiero, 

 and Giudicaria), showed that Werfen-slates, resting on mica- schist 

 or on porphyries, and containing veins of carbonate of iron near Pri- 

 miero, prevail over a great area. These slates have undergone con- 

 siderable upheavals near Villarzano and Ravina, south of the Adige. 

 The western range of the Werfen-slates, from Rancon to Dimaro, is 

 nearly always gypsiferous, and is overlaid by rather thin strata of 

 Guttenstein-limestones. Hallstadt-limestone and dolomite are con- 

 fined to the region between Roncon, Tione, and Dimaro ; the upper 

 shell-limestone of the St.-Cassian-strata to the Giudicaria. The fer- 

 ruginous oolites of Vigolo and Roncogno, west of Pergine, may pro- 

 bably belong also to the St.-Cassian-group. The Dachstein-dolo- 

 mite occupies also an extensive area. The oolitic rocks resting on it 

 are powerfully developed between Primiero and Val Sugana, also 

 between the Sarca, the Adige, and the Lake of Molveno ; they are 

 full of characteristic fossils near Cadina (Tridentine) and Rozzo 

 (Sette Communi). 



Another far-spread rock is the red and light-grey Ammonite-lime- 

 stone of the Upper Jura. It is overlaid by the nearly white Neoco- 

 mian limestone (Biancone) ; and this by Cretaceous marl-slates, of 

 an intense red colour (Scaglia). 



The Eocene period is represented by Nummulitic limestones ; the 

 younger Miocene by shelly marls and insignificant lignite-beds. Di- 

 luvial gravel is extensively deposited in the Giudicaria. Abundance 

 of good peat occurs over marly slates near Fiave, south of Stenico. 



[Count M.] 



