Vol. 55.] THE TOKSION-STETJCTURE OF THE DOLOMITES. 579 



(2) The torsion -phenomena. — Another new and far more 

 striking feature in the geology of the Pass is the abundant evidence 

 that the most conspicuous crust-movement has been one of crust- 

 torsion J My own observations illustrative of torsion at theGroden 

 Pass may now be classified, reference being understood to the 

 scheme, map, and sections :- — 



1. Torsion of the strike of the strata. — The strike of the rocks in the 

 various fault-blocks of the anticline veers round from longitudinal to oblique 

 directions. 



2. Distortion of the anticline. — The anticlinal 'buckle' (Lapworth) 

 is asymmetric, divided into two unequal wings by the Plon fault. Both wings 

 are well exposed on the western slope, where they form together an anticlinal 

 fan of fault-blocks, expanding broadly in the Grroden Valley. On the eastern 

 slope, the northern wing is well exposed on the Pass, but vanishes below Varda 

 in the Enneberg Valley. While the southern wing is represented on the Pass 

 only by the higher horizons of strata, it is fully exposed on the Langs-da-fiir hill 

 above the Valley. The anticline, therefore, shows considerable variation within 

 narrow spacial limits. 



What can be actually seen in the Pass structure is a number of separate 

 fault-blocks, twisted obliquely away from a central convergent area ; and the 

 wider fault-gaps (and many of the narrower) filled up by intrusive rocks and 

 fault- breccias. What may be deduced from the Pass structure is that if the 

 intrusive rocks could be melted away, and the fault-blocks of stratified rock 

 could be pulled back into line one with another on the opposite slopes of the 

 Pass, the form obtained would be that of an anticlinal fold, the axis of which 

 runs centrally along the Pass in the direction of its length, or, in other words, 

 traverses the Pass in its meridional direction. 



3. Opposite fold-arcs curving away one from another. — The 

 distortion of the anticline in its several parts is such that no two sections 

 through it show the same relations (compare figs. 1 & 4, pp. 568 & 572). 



The northern wing curves from west-north-west round a southern arc to east- 

 north-east, and has been overcast southward into the form of a knee-bend with 

 overthrusts at different parts towards the south-south-west and south-south- 

 east ; normal faults curved in the same sense as the reversed faults have thrown 

 down the strata to the north towards the Dolomite-clifis of Spitz Kofi and 

 Tschampatsch. 



The southern wing curves from west-south-west round a northern arc to east- 

 south-east, and is cut by the Pitzculatsch Fault. The adjoining cliffs of Sella 

 exhibit a back-fold curved in the same sense, but rather more south-west and 

 south-east. An overthrust-plane cuts this back-fold, the overthrust taking place 

 towards the north-west, north-north-west, north-north-east and north-east. 

 This is, therefore, a return overthrust to northward, compensating the overthrust 

 to southward in the northern wing of the anticline. 



1 The crust-movements concerned in bringing about the present structure 

 of the Grroden Pass and the region of which it forms a part, embrace not only 

 those of folding, faulting, overfolding, overthrusting, etc., as usually under- 

 stood, but in addition, and even more conspicuously, those which are commonly 

 grouped under the head of torsion. 



Those geologists who are familiar, on the one hand, with the advances made 

 during the last quarter of a century in knowledge and in speculation respecting 

 crust-deformation, by means of folding and faulting, normal or overthrust in 

 effect, and parallel, orthogonal, or oblique in direction ; and, on the other 

 hand, with the remarkable torsional results worked out by Daubree in the 

 laboratory, and by Lossen and others in the field, will have no difficulty in 

 recognizing for themselves what tectonic principles and results are new in the 

 present paper, and what have been derived from, or anticipated by, the work 

 and deductions of others. As respects the terminology employed, reference 

 may be made to the works of Heim, de Margerie, Suess, Bertrand, Lapworth, 

 Peach & Home, Daubree, Lossen, etc. 



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