^^^' 55-] TOKSION-STKUGTURE OF THE DOLOMITES. 627 



The opposite Dolomite-mountains represent torsion -segments 

 curving away one from the other and from the torsion-axis along 

 the various correlated oblique directions, as already demonstrated in 

 the cases of Sella and Sett Sass. These examples of oblique torsion- 

 systems along one and the same original line of strike suffice to 

 prove the general application of torsion to the complicated strati- 

 graphy of the neighbourhood. The complications would not have 

 arisen, had not Permian and Middle Triassic flexures previously 

 existed in another direction of strike than that called forth by 

 the horizontal forces acting during the later uprise of the Alps. 



On the other hand, all the faults are reduced to order, when it is 

 recognized that the area has been broken up into a number of 

 individual torsion-systems in each of which the strike has under- 

 gone the necessary change. Adjacent systems are separated by 

 cross-faults, many of which give evidence of having continued 

 to act as planes of adjustment after torsion had taken place (see 

 also p. 574). 



Strike-torsion at Eassa. — In order to investigate further 

 the action of the later horizontal forces of compression and torsion, 

 one of the torsion-axes of strike must be followed. The new strike- 

 axis of Col di Lana and Cima di Rossi, which lie east-north-east 

 and west-south-west across the Buchenstein Yalley, curves south- 

 west at Canazei and passes obliquely across the Passa Valley. There 

 it forms the torsion-axis of a system in which the southern spurs 

 of Rosengarten branch at the north-western area of subsidence, 

 and the diagonally opposite, south-eastern area is occupied by the 

 Vallaccia and Monzoni group (fig. 22, p. 630). The Buchenstein and 

 the Fassa axes form together one torsion-curve veering from west- 

 south-west to south-west. A parallel axis of torsion farther south 

 passes through the ' eruptive ' area of Fleims and Predazzo. The 

 torsion-axis may be said to lie in the eruptive rocks, while areas of 

 subsidence are present all round the eruptive centre except on the 

 south-east side. The Latemar group occupies the area of subsidence 

 on the north-west side of the Pleims axis, and the dolomite-rocks 

 of Yiezzena and Dosso Capello lie south of the axis. The torsion- 

 curve in both these cases is a curve which is characteristic of the 

 Judicarian-Asta system of faults (pp. 577 & 602, footnotes). 



The angle of torsion through which the old east-and-west strike 

 was shifted was much greater at Fassa and Fleims than at Buchen- 

 stein ; and the eruptive group of Yiezzena and Predazzo occurs where 

 the torsion-curve crosses the original strike at an angle of about 45°, 

 that is, where the torsion was unusually pronounced. At the same 

 time, the area is proximal to the Permian porphyrJ^ The inevitable 

 conclusion is that eruptive activity broke out in that area afresh as 

 a result of torsion, and must therefore have occurred at a 

 fairly advanced stage of the torsion. The latest outbreaks in 

 the area may be identified with the most acute phase of torsion, since 

 the transverse, as well as the diagonal, faults which cut the main 

 overthrusts and torsion strike-faults of the Groden-Pass and the 

 Buchenstein- Yalley systems are occupied by fault-dvkes, radially 



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