﻿Vol. 6 1.] DOLOMITES OF SOUTHERN TYROL. 115 



some of the dolomites of Raibl age. At the close of the Raibl 

 period a further depression of the district became general, and 

 thoroughly-marine conditions supervened. The first-formed Dach- 

 stein deposits were probably of the nature of coral-reefs, since 

 the base of the dolomite is very free from residue. The bedded 

 character of most of the deposit and its fossil contents make it 

 probable that, for the greater part, it was of sedimentary origin, and 

 Profs. Doelter & Hoernes record two analyses from the upper part 

 of the mass in which the residue approaches 1 per cent. 1 



IV. The Mineralogical Evidence. 



About eighty of the specimens collected were sliced, with a view 

 to the examination of any organisms which might be recognizable, 

 and for the study of the mineralogical characters exhibited by the 

 various limestones and dolomites. The results of the examination 

 of the sections of Schlern Dolomite will be considered first, and 

 afterwards the results obtained with rock-sections from other 

 horizons will be stated briefly. 



The Schlern Dolomite. 

 Area of the Schlern. 



No. 7. Bedded dolomite, from the edge of the Schlern plateau. 



Transverse and longitudinal sections of echinoderm-spines occur, 

 while similarly-orientated coral-sections are recognized somewhat 

 doubtfully, owing to loss of structure duriug dolomitization. Both 

 allotriomorphic and idiomorphic crystals of dolomite are present, the 

 idiomorphic crystals having cloudy centres. Minute iron-stained 

 patches scattered throughout the section may represent finely- 

 divided volcanic matter. 



No. 8. About 500 feet below the edge of the Schlern plateau. 



No organisms can be identified. The former presence of corals 

 may perhaps be inferred from the meandrine arrangement of those 

 dolomite-crystals which have regularly-arranged dark centres. 

 Minute brown inclusions present are almost isotropic, and may be 

 volcanic. 



No. 10. About 800 feet below No. 8. (See PI. XI, fig. 1.) 



The section consists largely of allotriomorphic, dark-centred 

 dolomite-crystals exhibiting a meandrine arrangement. Some minute 

 opaque iron -stained fragments are to be seen. 



No. 11. About 300 feet below No. 10. 



No organisms have escaped the loss of structure consequent upon 

 dolomitization. The section consists of allotriomorphic cloudy 

 crystals of dolomite, with scattered fragments of magnetite and 

 green augite, the latter being similar in appearance to the pyroxenic 

 constituent of the tuffs and lavas of the Seiser Alp. 



1 Jahrb. d. k.-k. geol. Eeichsanst. vol. xxv (1875) pp. 322, 323. 



i 2 



