Yol. 55.] TORSION-STRUCTUEE OF THE DOLOMITES. 623 



(4) A series of foiu" crust-whorls was determined by the inclined planes of 

 the fault-curves. The lowest whorl is exposed in Middle Trias, and partly in 

 Lower Trias ; it passes through Langs-da-Fiir, Campolungo, Cherz, Monte Sief, 

 to Castello, and is characterized by inclined faults towards the Pralongia and 

 Sett Sass basin, and intrusive porphyrite in the faults. The succeeding whorl 

 is exposed in the Wengen-Oassian Series and passes through the Ruones, Pra- 

 longia, Montagna della Corte, and Castello meadows. It is characterized by 

 overthriist southward, and steep flexure northward towards Stuores and the 

 southern curve of Sett Sass. The next whorl is fragmentary, being represented 

 by the Cassian and Schlern-Dolomite rocks composing the Richthofen Reef and 

 the continuation of that slice round the western and southern curvature of Sett 

 Sass. This fragment also shows overthrust southward and steep northward 

 flexure. The highest whorl in this basin is that of the Upper Trias composing 

 Sett Sass, which has been overthrust southward above the Richthofen Eeef and 

 bent steeply northward towards Eisenofen. All four whorls are incomplete on 

 the .east side of the basin, where they are cut by cross-faults. 



(5) The most important tectonic feature is the result of the particular com- 

 bination of normal and reversed faults similarly inclined, but with very different 

 angles of inclination. The most compressed portion of the area is at Monte 

 Sief and Sett Sass, where the series of faults is as follows : — 



p, .fa. Highly inclined normal fault at Monte Sief. 



ii-lanes meet I ^ Moderately „ reversed „ at Montagna della Corte. 



upwara. [ ^_ Slightly „ „ „ at the Richthofen Reef. 



Planes meet ( d. Moderately ,, normal „ in Sett Sass. 



downward. \ e. Highly „ reversed ,, at Eisenofen. 



The grouping of these inclined faults is such that increased compression 

 tended to bring the mass of strata composing Sett Sass nearer the strata of 

 Monte Sief and Col di Lana. 



Appendix. 



Analogy of Monte Sief with Eodella Hill. — The diagonal 

 fault between Sasso di Stria and Sett Sass has eflPected a lateral 

 southward displacement of the strata which composed the east-and- 

 west anticline of Cima di Eossi, Belvedere, and Col di Lana. The 

 eastward continuation of this anticlinal buckle of older Trias and 

 lava must be sought some distance south of the Nuvolau and 

 Camera Dolomite-massives, 



The diagonal fault west of the Sasso di Stria arch is parallel 

 with the diagonal fault of the Sella arch, and these two faults form 

 the eastern and western limits respectively of the area of torsion 

 described in the foregoing pages. These are definite confines, 

 which limit a four-sided area, influenced by the Groden-Pass torsion- 

 system on the north and the Buchenstein torsion-system on the 

 south. The area is a typical torsion-unit in the Dolomites, and 

 displays in a marked degree the phenomena of interference cross- 

 faults, cutting a series of peripheral overthrusts round the synclines, 

 and parallel flexure-faults between the anticlinal buckles and the 

 synclinal basins. 



Both the limiting diagonal faults displace the outcrop of the 

 Belvedere-Buchenstein Anticline towards the south : that is, they 

 eff'ect downthrow on their east side. Eodella is present, west of 

 the Sella Fault, as a curious torsion-block of older rock in the imme- 

 diate vicinity of the torsion-basin occupied by the Platt-Kofl and 



