﻿Vol. 6 1.] THE DOLOMITES OF SOUTHERN TYROL. 



8. On the Chemical and Miner alogical Evidence as to the Origin 

 of the Dolomites of Southern Tyrol. By Prof. Ernest 

 Wellington Skeats, D.Sc, F.G.S. (Read December 7th, 

 1904.) 



[Plates X- XIV — Microscope-Sections.] 



I. Introduction. 



The country of the ' Dolomites ' has long been classic ground to 

 geologists. The researches of Dolomieu 1 at the end of the eighteenth 

 century, and of L. von Buch 2 early in the nineteenth, first aroused 

 the interest of geologists in the district. Their attention at first 

 was mainly directed to speculations concerning the mode of origin 

 of the mineral, named after the French geologist, of which the moun- 

 tains are so largely composed ; this question, even at the present 

 day, is far from settled. The stratigraphy of the district has 

 always presented many points of difficulty. The earlier observers, 

 struck by the contrast in scenery and composition between the 

 bold, precipitous, dolomite-masses and the marls and stratified tuffs 

 of the green pasture-lands or ' Alpen,' were at a loss to explain 

 their mutual relations, especially as very few fossils were at first 

 discovered in any of the deposits. In 1834, however, Graf Miinster,'' 

 who had examined the strata near St. Cassian, enumerated, and (in 

 part) described and figured 400 species of fossils from them, and 

 subsequent observers have added largely to the number. The precise 

 age of these deposits, which had till then been a matter of discussion, 

 was settled by the examination of their fossil contents. It was shown 

 not only that the beds were of Triassic age, but that, unlike the Trias 

 of most of the European areas, they had been deposited under marine 

 conditions. In 1845 Bronn 4 suggested that the St. Cassian fauna had 

 inhabited a shallow sea where coral-banks were numerous. 



The stratigraphy of the district was first systematically described 

 by Baron Ferdinand von Bichthofen, 5 in a brilliant paper, in which 

 he claimed that the curious relations of the dolomitic and non-dolo- 

 mitic strata could be explained if it were assumed that the masses 

 of dolomite represented altered coral-reefs formed during a period 

 of subsidence, while the St. Cassian marly and tufaceous deposits 

 were laid down in the lagoons, bays, and channels of a coral-sea. 



" x ' Observations sur la Physique, &c.' vol. xxxix (1791) p. 3. 



2 ' Ueber Dolomit als Gebirgsart ' Abhandl. d. k. Akad. Wissensch. Berlin, 

 1822-23 & ' Einige Bemerkungen iiber die Alpen in Baiern ' ibid. 1828, p. 84. 



3 Neues Jahrb. 1834, pp. 1-15 & pis. i-ii; see also ibid. 1842, p. 119. 



4 Rid 1845, pp. 504-508. 



5 ' Geognostiscke Beschreibung der Umgegend von Predazzo, St. Cassian & 

 der Seisser Alpe in SM-Tyrol' Gotba, 1860, 4to. 



Q. J.G. S. No. 241. ii 



