590 MISS M. M. OGILYIE [mRS. GOEDOlSr] ON THE [Aug. 1 899, 



East-aud-west cross-faults limiting the Buchenstein 

 torsion -system. — The western extremity of the Belvedere 

 ridge, named Cima di Rossi, is separated from the Eodella Hill 

 complex of similar rocks by the fault over the Sella Pass (p. 570) 

 towards Canazei. This transverse fault is accompanied here by a 

 fault-dyke continuous with the intrusive sheet in the strike-shears. 

 The Eodella fault-block west of the transverse fault has been twisted 

 in counter-clockwise direction to the east-north-east, and the Cima di 

 Eossi block, east of the transverse fault, has been twisted also in 

 counter-clockwise direction, but to the west-south-west. Eeferring 

 to the diagram of torsion (fig. 8, p. 581), the Eodella block and the 

 Cima di Eossi block represent the B & D force-spirals respectively 

 in two adjacent torsion-systems. 



Again, the downthrow of the transverse fault is on the east side, 

 towards Sella ; the fault therefore neutralizes the sum of the diagonal 

 faults through Soraruaz, Campolungo, and Bova Alp (p. 599), whose 

 downthrow is in all three cases on the west side, towards Sella. 



The limiting cross-fault east of the Buchen stein torsion-system 

 is the Yalparola Fault, with an easterly downthrow. 



If we now in imagination turn back the intercrossing axes of the 

 torsion -strikes into straight line one Avith another, Cima di Eossi 

 would be brought into touch with Eodella at the western extremity 

 and Col di Lana with Monte Padom at the eastern. 



Superposition of Tertiary upon Triassic strike. — 

 I previously pointed out the obliquity of Tertiary lines of crust- 

 movem.ent to pre-existing lines of Triassic disturbance (see p. 563). 

 The probable relation of the later movements to the earlier may 

 now be indicated, in accordance with the results obtained. 



A Middle Triassic flexure or fault, with an east-and-west strike in 

 this particular locality, was acted upon obliquely during the Tertiary 

 upheaval by combined movements of compression and torsion, after 

 the manner described in the case of the Groden Pass. While the 

 new movements apparently concentrated themselves along the pre- 

 existing lines of crust-weakness, the new crust-buckles took shape 

 across the former strike in the form of cross-folds, and the move- 

 ments culminated in oblique shears and diagonal and transverse 

 ruptures, accompanied by the injection of dykes and sheets in the 

 curved faults. The overlapping or virgating shear-wedges of torsion 

 then gradually adjusted themselves in the new directions of strike, 

 while adjacent fault-blocks settled themselves on opposite sides of 

 the diagonal and transverse ruptures, such movements of adjustment 

 taking place along fault-planes primarily determined during the 

 period of active torsion. 



IV. The Sella Massive. 



The Sella Massive presents a highly characteristic type of the 

 mountains in the Southern Tyrol Dolomites. 



The geological map published by Mojsisovics^ gives expression 

 to the theory that Sella Mountain was pre-eminently a coral-reef 



^ ' Die Dolomit-Eiffe von Siid-Tirol u. Venetien,' 1879, chap, viii, pp. 227-240. 



