Yol. 55.] THE TORSION- STKUCTUEE OP THE DOLOMITES. 589 



First, one observes that the divergent faults east of the Soraruaz 

 diagonal fault curve variously north-eastward and south-eastward, 

 whereas the faults west of the Soraruaz Fault curve north-westward 

 round Cherz, and south-westward through the Arabba Hills. 

 Further, that the chief oblique faults intersecting the eastern fault- 

 bundle are north-north-west and south-south-east in direction, 

 whereas those across the western bundle are north-north-east 

 and south-south-west in direction, becoming north-east and south- 

 west and east-north-east and west-south-west in the strongly- 

 compressed part of the Cherz Hill curve. 



From a knowledge of the Groden Pass and a comparison of figures, 

 it is not difficult to recognize two oj)posite fold-arcs, meeting in a 

 central area (Soraruaz) of fold-intersection and maximum torsion- 

 shear. The torsion force-couples have induced clockwise torsion 

 in the north-western and south-eastern quarters, counter-clockwise 

 torsion in the north-eastern and south-western quarters. 



If a straight line be now drawn from Canazei in the Avisio Valley, 

 through the area of intersection and north of Monte Sief, to meet 

 the Yalparola stream, the line will have a west-south-westerly and 

 east-north-easterly direction parallel with the line followed by the 

 main torsion-fault of the Groden Pass. Such a line, moreover, will 

 be found to correspond with an actual line of contact in nature, 

 between an intrusive igneous sheet and the Wengen strata exposed 

 on the Pordoi, Sella, and Cherz slopes. The natural line varies 

 from the drawn one only where the former follows the contours of 

 Campolungo and Cherz above the Arabba stream. The line from 

 Canazei to the Yalparola stream is recognizable as the chief torsion- 

 strike, while a subordinate torsion-strike runs from west-north-west 

 (Cherz Hill curve) to east-south-east (Pieve and Cordevole Yalley 

 curve). 



The complete torsion-system of Buchenstein may be embraced 

 within an elliptical outline, and, just as in the case of the Groden 

 Pass, there are opposite areas of subsidence behind the northern 

 and southern wings of the anticline I'espectively. Sella and Sett 

 Sass represent two segmented portions of the northern synclinal 

 area separated by the diagonal buckle of Campolungo, while the 

 Marmolata mountain represents the southern synclinal area. 



Relation of Col di Lana to the Belvedere ridge. — 

 The petrographical similarity between the rocks of Col di Lana and 

 Cherz Hill on the one hand, and those of the Belvedere ridge on the 

 other, has been the subject of frequent comment by geologists. The 

 apparent thickness of the rock-complex on Col di Lana and Cherz 

 Hill is due to the occurrence of the overthrust-planes. Now, the 

 system of torsion-faults set forth above explains Col di Lana and 

 Cherz Hill as obliquely-twisted segments forming the northern fold- 

 arc of the Buchenstein Anticline, whose southern fold-arc is formed 

 by the Belvedere ridge. Thus, instead of Col di Lana representing 

 an individual centre of eruption in Middle Triassic time, as suggested 

 by some, it is shown by its stratigraphy to have been originally a 

 homogeneous part of the Belvedere body of strata. 



