﻿Vol. 6 1.] DOLOMITES OF SOUTHERN TYROL. 117 



centred dolomite-crystals. Some of the dark centres of the crystals 

 are composed of calcite, as they are stained by Lemberg's solution. 

 The majority of the crystals are cavernous on a microscopic scale, 

 and this gives the appearance of cloudiness to these individuals. One 

 clear crystal of orthoclase, showing both cleavages, is to be noted, 

 and exceedingly-minute, dark-reddish to opaque particles are possibly 

 of volcanic origin. 



No. 92. Above the bedded dolomite, at the head of the valley 

 above Wolkenstein. 



An allotriomorphic, slightly-cavernous dolomite. The former 

 presence of meandrine organisms is indicated by the arrangement of 

 the dolomite-crystals with dark centres. 



Area of the Marmolata. 



No. 35. Southern shore of the Fedaja See ; from a height of 

 6500 feet. 



A limestone crowded with small branching structures, which 

 under the quarter-inch objective appear to be chambered. 



A few dolomite-crystals and fragments of crystals are present. 

 Some of these have regularly- arranged dirt-inclusions, while others 

 consist of alternate zones of dolomite, calcite, and again dolomite. 

 Meandrine patches of cloudy material represent decomposed 

 organisms. Much of the calcitic groundmass is cloudy, and polarizes 

 not in distinct crystals, but as an aggregate. Planes of movement 

 and recrystallization are noticed in places. Where recrystallization 

 has resulted in the formation of large twinned and cleaved crystals, 

 these are in places found to be crowded with minute acicular 

 bodies. At first these seem to be opaque, but when closely examined 

 they are seen to be translucent. 



One fragment, possibly volcanic, is present. 



No. 34. West of No. 35 and lower down the valley, northern part 

 of the Marmolata. 



Similar generally to No. 35. The branching chambered structure 

 is common. The section has been stained with Lemberg's 

 solution, and some of the branching structures appear to be 

 cavities in the slice filled with the stain, since they do not affect 

 polarized light. The great majority, however, show pclarization- 

 colours, and, as is usual with organisms, they are stained more 

 deeply than the background. Most of the slice consists of 

 calcite, twinned and cleaved, and showing planes of movement 

 and small veins of secondary calcite. A few crystals and fragments 

 of idiomorphic dolomite occur. Some of the fragments look clastic, 

 and extinguish not 'uniformly but as an aggregate, which would 

 suggest that a secondary change in the mineral had occurred. 



No. 33. A few feet above No. 34. 



No dolomite is present, and planes of movement are very con- 

 spicuous. In other respects it closely resembles Nos. 34 & 35, 

 and the branching structure is again common. 



