﻿114 PROF. E. W. SKEATS ON THE [Feb. I905, 



the dolomite rests upon limestones and marls, named after St.Cassian, 

 where they are well seen. They are for the most part earthy lime- 

 stones, oolitic in places, and probably of detrital origin, since for 

 the most part they contain a rather large amount of residue. 

 Locally, as at Sett Sass, they become very rich in beautifully- 

 preserved branching corals, and an analysis of one of these shows 

 that, while it is very ferruginous, it is almost devoid of insoluble 

 residue. On the Seiser Alp, intercalated with the volcanic tuffs 

 of St. Cassian age, lenticular masses and blocks of limestone or 

 dolomite, which are known as ' Cipit '-limestone, occur. An analysis 

 of a specimen taken from one of these blocks shows it to be highly 

 dolomitic and to contain surprisingly-little residue ('73 per cent.), 

 considering its intimate association with the St. Cassian tuffs. As 

 these blocks not infrequently contain reef-forming corals, there seems 

 little doubt that they represent scattered reef-like patches of corals, 

 which established themselves during a temporary abatement of 

 volcanic activity in the areas in which they are found. 



An analysis of one of the earthy Wengen limestones found on 

 the northern slopes of the Seiser Alp, shows a great admixture of 

 insoluble matter, probably volcanic in origin. Proximity to land is 

 indicated by the local occurrence (in the Gader Valley, for instance) 

 of plant-remains in the Wengen deposits. 



The Buchenstein Limestones, while not so earthy as those of 

 Wengen age, are shown in two cases to contain between 7 and 

 9 per cent, of residue, and are probably of detrital origin, as 

 contemporaneous volcanic rocks of Buchenstein age appear to be rare. 



The Mendola Dolomite contains over 40 per cent, of magnesium- 

 carbonate, and rather less than 1 per cent, of residue in the two 

 examples analysed. It presents, therefore, a considerable resem- 

 blance to some of the Schlern Dolomites, and may have been formed 

 as a reef to which some detrital material had access. 



The only remaining limestones from the Older Triassic rocks are 

 of Lower-Muschelkalk age. These are very impure, an analysis of 

 one from the Gader Gorge showing over 30 per cent, of residue. 

 They are, in all probability, of detrital origin. Possibly the older 

 crystalline rocks of the neighbourhood were not entirely submerged, 

 and these would serve to account for the presence of so much 

 insoluble matter. 



After the formation of the Schlern Dolomite the area of deposition 

 was restricted, in consequence of 'negative movements' ; some of 

 the area was raised above sea-level, and the succeeding Raibl Beds 

 were laid down in lagoons, salt-water lakes, etc., for we find that in 

 different places the Piaibl deposits vary greatly in character. Reddish 

 marls, sandstones, gypsum, dolomite, and patches of coral are all 

 represented. Possibly some of the magnesium in these beds is to 

 be attributed to direct^ deposition from concentrated salt-water, 

 and the erosion and solution of some of the Schlern Dolomite, as 

 well as the presence of minute Volcanic fragments, would suffice 

 to account for the 3 or 4 per cent, of insoluble residue found in 



