618 MISS M. M. OGILVIE [mRS. GORDON"] ON THE [Aug. 1 899, 



Sett Sass, but assume irregular relations with respect 

 to the Richthofen Eeef. The strike-readings are north 45^ west 

 above the Eichthofen lieef, veering to north 60"^ west a little 

 eastward, and to east and west still farther east. The dip varies 

 from 25° northward above the Eichthofen Eeef to 60° farther east ; 

 and still farther east the strata are tilted almost vertically. The 

 Schlern-Dolomite rock of the Eichthofen Eeef is reall)^ at a higher 

 level than that occupied by the Cassian strata in the col between 

 the Eeef and Sett Sass. Such rapid variation along the plane 

 between the Cassian strata and the underlying Schlern Dolomite 

 would in itself suggest some stratigraphical disturbance of the 

 nature of a thrust-plane. 



' Dolomite '-rock forms only the upper half of the Eeef, and 

 very rapidly thins out eastward. The lower half of the Eeef is 

 separated from the upper half by an inclined joint- 

 plane. The lower half consists of the brownish-yellow limestones 

 which mark the uppermost horizons of Cassian rocks all round 

 Sella, at Crap de Sella, on Pralongia, and elsewhere. 



Another joint separates this lower half of the Eeef-rock from a 

 thin basal grey limestone. I followed all three horizons of the 

 reef both eastward and westward, and found that soft Cassian 

 marls gradually appeared along the continuation of 

 these inclined 'joints'; I regard the inclined joints 

 as subordinate shear -planes associated with a main over- 

 thrust-plane above the Eichthofen Eeef, upon which the fossiliferous 

 soft- bedded Cassian marls have been overthrust southward above the 

 higher horizons of Cassian limestone at some points, and for the most 

 part, and above Schlern Dolomite at the Eichthofen Eeef. 



The map (PL XL) and section (fig. 10, p. 586) perhaps explain the 

 relations better than a verbal description. Combined with the 

 overthrust there has been a differential twining movement in the 

 sense of the B-spiral. The overlay of the fold has been twisted 

 south-eastward, while the underlay has been twisted north-westward. 

 The easterly shear-faults denote segmentation of the underlay due 

 to torsion. 



Peripheral overthrust round the west of Sett Sass. 

 — A curvature of the peripheral overthrusts takes place where the 

 diagonal Eisenofen arch (p. 617) crosses the overthrust. The mode 

 of torsion of a thrust-plane under such conditions has been demon- 

 strated already in several cases. Here torsion of the strike of the 

 strata has been effected from east and west on the south to north-west 

 and south-east on the west, while the shear-faults run north and 

 south. 



A series of narrow ridges diverge from the diagonal fault on the 

 west side of the Eisenofen arch. They radiate from the curvature 

 of the cliffs westward and north-westward, and are composed of 

 Eaibl strata, massive Dachstein-Limestone blocks, and, in less 

 number, Schlern-Dolomite blocks. The Eaibl rocks are clearly in 

 their true position, as thej^ may be followed at about the same level 

 along the base of the western cliffs. The Dolomite-blocks are 

 largely fallen masses. 



