90 Reports and Proceedings — Oeological Society of London. 



The area of movement of the Groden Pass system is an ellipsoid 

 in form. Two foci occur within it, where the effects of shear and 

 (strain have culminated. The forces of compression acted not in 

 parallel lines, but round the area, thus causing torsion of the earth- 

 crust. Two main faults occur (with a general east-and-west trend) 

 whose actual lines of direction intersect at a point about midway 

 between the foci of the torsion-ellipsoid. These are the chief strike 

 torsion-faults ; many minor ones pass out easterly and westerly from 

 the foci, forming longitudinal or strike torsion-bundles. The strike 

 system of faults is cut by a series of diagonal or transverse curved 

 branching faults, with a more or less north-easterly or north- 

 westerly direction. These diagonal faults may cut each other, or 

 may combine to form characteristic torsion-curves. The author 

 regards the longitudinal and diagonal faults as constituting one 

 system. Each portion on one side of the anticlinal form of the 

 system has its reciprocal on the other side. The Spitz Koti syncline 

 on the north is the reciprocal of that of Sella on the south, the 

 Langkofl on the south-west of that of Sass Songe on the north-east, 

 and so on. 



The anticlinal area of the Buchenstein Valley is next described. 

 Here we have a torsion-system similar to that of the Groden Pass, 

 and made up of similar elements ; but the western portion of the 

 anticlinal is much compressed and displaced. Opposing areas of 

 depression are also found here, that of Sella and Sett Sass on the 

 north being reciprocated by that of the Marmolata on the south, and 

 so on. The porphyrite-sills have here been mainly injected into the 

 knee-bends of the northern wing of the anticlinal form, but igneous 

 injections and contact-phenomena are also met with in some of the 

 transverse faults. 



A full description is given of the sequence and stratigraphy in 

 the Sella massive — once regarded by some authorities as a Triassic 

 coral-reef. This is an ellipsoidal synclinal area with N.N.E. and 

 S.S.W. axes twisted to north-east and south-west. Peripheral over- 

 thrusts have taken place outward from the massive, in such a way 

 as to buckle up the rocks like a broad-topped fan-structure, and these 

 overthrusts are traced by the author completely round the massive. 

 A central infold of Jurassic strata occurs on the plateau, where the 

 Upper Trias has been overthrust inwards on three sides of the infold. 

 The author next passes in review the results obtained in the areas 

 of Sett Sass, etc., and shows how they all present corresponding 

 tectonic phenomena. 



The district thus studied in detail by the author forms a typical 

 unit in the structural features of the Dolomite region. It is cut off 

 to the eastward by the limiting fault (north-and-south) of Sasso de 

 Stria, and to the westward by the parallel fault of Sella Joch. 

 These are definite confines, which limit a four-sided area, influenced 

 by the Groden Pass torsion-system on the north and the Buchenstein 

 Valley system on the south. The limits of this four-sided figure 

 include a compound area of depression (formed by the Sella and 

 Sett Sass synclinals) traversed by the diagonal Campolungo buckle. 



