﻿112 PROE. E. W. SKEATS ON THE [Feb. I905, 



and so numerous that the rock assumes the character of a submarine 

 calcareous tuff. In this connection it may be mentioned that a 

 partial analysis of the insoluble residue from specimen No. 7, near 

 the Schlern plateau (p. 103), gave 64-26 per cent, of silica and 23*23 

 per cent, of ferric oxide and alumina. Slight reactions for calcium, 

 magnesium, and sodium were obtained, and a stronger indication of 

 the presence of potassium. A short distance below the summit of 

 the Schlern, on the southern and western sides, a later outpouring 

 of the augite-porphyry lava is interbedded with the Schlern 

 Dolomite. 



Area of the Langkofl. 



The two specimens which contain much residue come from 

 material lining the steep eastern slope of the mountain, and 

 possibly represent a reef-talus. Analyses from the solid mass of 

 the mountain show only a trace of residue. This, in conjunction 

 with the great thickness of the deposit, supports the view that it 

 was a coral-limestone formed during subsidence. 



Area of the Marmolata. 



Of the specimens collected in situ, two contain no residue, and 

 two analysed by Profs. Dcelter & Hcernes l are similarly free from 

 insoluble matter. The only specimen containing an appreciable 

 quantity (-6 per cent.) was collected from near the junction of the 

 dolomite with the contemporaneous lava poured out to the north of 

 the area. The facts again favour the view of the formation of the 

 deposit as a coral-limestone during a period of subsidence. 



The three areas just considered were subjected to similar condi- 

 tions of deposition, during a movement of subsidence commencing 

 not later than the Wengen period (in the Schlern area it commenced 

 in the Upper Muschelkalk period), and continued until a 'negative' 

 movement which set in at the commencement of the Eaibl period. 



In the remaining areas to be considered, the formation of the 

 deposit, which now consists mainly of dolomite, did not commence 

 until after the deposition of the Lower St. Cassian Marls and Lime- 

 stones. It is not surprising to find, therefore, that the dolomite is 

 much thinner than in the areas already considered ; at Tre Croci, 

 near Cortina, for instance, the thickness is reduced to about 300 feet. 



St. Cassian Dolomites. 



Area of the Sella. 



An examination of the results of analyses from the dolomite of 

 the Sella shows a progressive decrease in the amount of residue 

 present, from below upwards. It would seem that to the north 

 and east of the Schlern, Langkofl, and Marmolata massifs we 



1 Jahrb. d. k.-k. geol. Eeichsanst. vol. xxv (1875) p. 319. 



