Yol. 55.] TORSION-STETJCTITRB OF THE DOLOMITES. 591 



formation built during the Wengen, Cassiau, and Eaibl periods, 

 having been formed in continuity with the 'Lang Kofl Eeef ' during 

 Wengen and part of Cassian time. The following paragraphs 

 give an account of the researches made and conclusions arrived at 

 by the present author in the years 1892-1896. 



Structural significance of the ravines of Yal la 

 Stries and Yal di Mezzodi. — The Sella Massive occupies an 

 area of subsidence, elliptical in outline. The Groden Pass Anticline 

 curves round it on the north, the Cima di Rossi portion of the 

 Buchenstein Anticline curves round it on the south ; the Campo- 

 lungo diagonal buckle limits it on the east, and on the west the 

 diagonal buckle of the Sella Pass dips towards it. 



Two long narrow valleys with precipitous sides run up into the 

 heart of the Sella Massive. The one is Pissadoi ravine, called also 

 Yal di Mezzodi, ascending from the Groden Pass south-south- 

 westward to the hanging glacier which descends from the Boe ridge ; 

 the other is Yal la Stries, ascending from the Sella Pass eastward 

 to the Boe ridge. Their axial lines would meet in the middle of 

 the mountain at a wide angle, and the direction of curve which 

 would thus be suggested is parallel with several important diagonal 

 fault-curves through the east side of Sella. It is, moreover, practically 

 the axis of the torsion-ellipsoid of Sella itself. 



The line of section shown in fig. 14 (p. 592) runs north-west 

 and south-east, as nearly as possible transverse to the direction of 

 this curve. A second line of section is also given north and south, 

 cutting transversely a subordinate direction of strike in the mountain 

 (fig. 16, p. 594). The strike of the rocks curves round from one 

 direction to another, holding parallel with the peripheral outline of 

 the massive. The dip is, in the main body of the mountain, 

 inward to the centre, but near the periphery the rocks, especially 

 on the south and east sides, dip outward. 



Pitzculatsch exposures. — The first part of the line of 

 section (fig. 14, p. 592) passes from Plon over Pitzculatsch to that 

 corner of Sella which is known as the Griiner Pleck, and thence 

 over the high precipices of the Meisules terrace. 



The Pitzculatsch Pault has been already described (p. 567). 

 South of it, in its immediate neighbourhood, true ' Buchenstein 

 limestone ' (see footnote, p. 569) is wedged into the grass of the steep 

 slopes in block-form, and probably represents sheared rock. The 

 dark, banded limestone and tufaceous strata at the base of the 

 Wengen Series have a considerable surface-outcrop, and can be 

 examined in stream-courses. The general strike is north 60° to 65° 

 east ; the dip is about 50°, but diminishes to 30° nearer Sella. 



A Cipit- Limestone horizon follows, which marks locally the limit 

 between Wengen and Cassian strata, and has been previously termed 

 ' Lower Cassian ' by the present author on account of its containing 

 the first indications of the Cassian fauna. Its character on the 

 Pitzculatsch slope of Sella is precisely the same as that which is 

 to be seen in the typical area of Priilongia.^ 



1 Quart. Journ. Geol. Soc. vol. xlix (1893) p. 16. 



