﻿Vol. 6 1.] DOLOMITES OF SOUTHERN TYROL. 121 



No. 62. Top of the north side of Col Crepa. 



A clear allotriomorphic dolomite, showing no signs of organic 

 structure, except in some parts of the section where cloudy crystals 

 are arranged in a meandrine fashion, suggesting the former presence 

 of corals. 



No. 64. A rock very similar to No. 62, a few feet below it. 



Giau Pass. 



No. 37. From the Giau Pass, about 6 miles south-west of Cortina. 

 Not in place. 



The slide shows a section of a coral preserved mainly in calcite. 

 The structure of the coral is nearly obliterated ; the external wall 

 can, however, be traced, and the septa are defined by linear bands 

 of dolomite- and calcite-crystals. Scattered through the coral occur 

 a large number of minute, perfectly-idiomorphic crystals of quartz 

 (see PI. XIV, fig. 2). They are doubly terminated, and can be 

 recognized by their shape, their grey polarization-colours, and their 

 positive sign, when examined with a quartz-wedge. Unlike the 

 quartz-crystals found in the Carboniferous Limestone of Derbyshire 

 and other areas, they are not cloudy with inclusions, but perfectly 

 clear and translucent. The longer diameters measure from -g^ to 

 -j-J^- inch. These crystals probably represent the colloid silica of 

 the skeletons of the siliceous organisms originally present in the 

 rock, which has been recrystallized. 



Many of the dolomite-rhombohedra show minute bands of calcite 

 extending through them, and coinciding in general with the directions 

 of the cleavage-lines but extending slightly on either side. They 

 possibly represent spaces formed by solution along cleavages, and 

 subsequently rilled with calcite. Staining with Lemberg's solution, 

 and examination with the quarter-inch objective, causes these 

 calcite-bands to be visible as fine pink lines. 



The Hexenfels. 



No. 56. From the base of the Hexenfels, near Falzarego Pass. 



A clear dolomite, partly granular but mainly allotriomorphic. 

 No organisms are visible, and specks of oxide of iron occur 

 sparingly. 



Travernanzez Valley. 



No. 59. Near the junction with the Raibl Beds, just below the 

 Col du Bee. 



A clear coarse-grained dolomite, devoid of organisms. 



Sorapis. 



No. 55. Schlern Dolomite from the flanks of Sorapis, 1 mile north 

 of San Vito del Cadore. 



A fairly coarse-grained dolomite, devoid of organisms. Specks of 

 a compound of iron are scattered through the section. 



