Vol. 55.] TOESION-STKUCTUEE OF THE DOLOMITES. 617 



includes the south-western summit (2434 metres) and is continued 

 northward to the Eisenofen huts. Flexure-faults directed north- 

 north-eastward and south-south-westward are again present — the 

 western with downthrow to the west, the eastern with downthrow 

 to the east. The most deeply sunk part of Sett Sass is the western 

 wing, which is wedged between the diagonal arches of Pralongia 

 and Eisenofen. 



Relation of the Sett-Sass Syncline to the Buchen- 

 stein Anticline. — Sett Sass represents a synclinal basin as deep 

 as that of Sella, and, like it, bounded by a polygon of faults with 

 downthrow to the mountain. As the map (PI. XL) shows, Monte 

 Sief and Col di Lana are at the east-north-eastern end of the twisted 

 Belvedere-Buchenstein Anticline, while Cima di Eossi is at the west- 

 south-western end. A steep northward flexure of the strata marks 

 the whole northern face of this anticline. 



In its proximity to this anticline on its south side, and in its 

 downthrow from the Cassian strata of Pralongia, Sett Sass offers a 

 precise analogy with the conditions affecting the south and east of 

 the Sella Massive. The resemblance became evident to me while 

 engaged in mapping the area of Sasso Pitschi, Pordoi Pass, and 

 Plan de Sass ; and it suggested a clearer interpretation of the 

 geology of Sett Sass than had occurred to me from my more limited 

 standpoint of 1892. 



The writer's map^ was reduced from the original survey, and 

 several of the details were omitted for the sake of clearness in the 

 reduced map. The accompanying map of the west and south sides 

 of Sett Sass is therefore given, with all the details as originally 

 entered on the Survey map on the scale of 95-QQQ (Ph XL). 



Peripheral overthrust round the southern curve of 

 Sett Sass. — The chief feature of the south side is the rock which 

 was called ' Pichthofen Piff ' by Mojsisovics and portrayed by him in 

 an excellent photograph.^ This so-called reef may be explained 

 in precisely the same way as tlie present writer explained Sasso 

 Pitschi,^ namely as a slice of Schlern Dolomite below an overthrust- 

 plane. 



Careful collection of the fossils in the Cassian marls overlying 

 the Pichthofen Peef, and as careful comparison of these with the 

 fossils found in the Cassian marls below the Peef and upon 

 Pralongia and Stuores meadows, made it impossible to determine 

 any zonal distinction. In short, the Cassian marls above and below 

 the Pichthofen Peef are identical both in respect of their fauna and 

 their petrographical character. 



With regard to the relations of strike and dip, these vary con- 

 siderably when they are followed round the southern curve of the 

 mountain. The Schlern-Dolomite rocks of Sett Sass strike east and 

 west, and di^D 12° northward . The Cassian strata dip regularly below 



^ Quart. Journ. Geol. See. vol. xHx (1893), map A. 



2 ' Dolomit-Riffe,' 1879, p. 248. 



3 ' Coral in the Dolomites,' Geol. Mag. 1894, p, 53. 



