^^^' 55-] TORSIOIf-STRUCTUEE OP THE DOLOMITES. 577 



force cross the strike, and at another part curve into the direction 

 of strike. In short, the fault-system is pre-eminently a fault- 

 network. Rapid variation in the throw of the fault is a marked 

 feature, and is associated with the frequent branching of faults. 



Similar features of overthrusting, rapid variation in the throw of 

 faults and in the precise angle of inclination of the fault-planes, 

 branching and curving of faults, have been demonstrated by the Aus- 

 trian geologists to be characteristic of the Judicarian-Asta system ^ 

 (cf. Suess) as presented in the Peri-Adriatic region of the Alps. 



(B) New Facts and Deductions respecting the Geology of 

 the Rocks of the Groden Pass. 



(1) The dyke-and-sill phenomena. — Evidences in the field 

 and the author's map and sections afford proof of dyke-and-sill 

 injections as an igneous network in the greater number of the 

 fault-planes of the Groden Pass, not only in the longitudinal or 

 strike-faults,^ but also in the diagonal and transverse faults. Evi- 

 dence is everywhere to be obtained that the fault-shearing must 

 have taken place while the igneous material was still a magma, and 

 could solidify round carried wedges, torn blocks, and the finest 

 fragments of faulted and invaded stratified rock. These shear- 

 and-contact breccias are typical ' fault-rock ' ; they have been 

 grouped hitherto by all observers as ' Buchenstein conglomerates 

 and tuff's,' and referred to the Middle Triassic period as a distinct 

 stratigraphical horizon. 



The present author's observations go to show that the injection 

 of the dykes and sills into fault-planes was associated with the origin 

 of the coarse shear- an d-con tact breccias, and took place in the last 

 epoch of intense crust-movements in the Groden Pass neighbourhood. 

 The development of the fault-system of the Groden Pass and Enne- 

 berg generally was demonstrated in my previous papers to have 

 been the Tertiary epoch of Alpine upheaval ; therefore the date of 

 origin of the so-called ' conglomeratic tuff" ' or ' agglomerate ' is not 

 Middle Triassic, but Tertiary. At the same time, there are true 

 lava-flows interbedded with the lower horizons of the Wengen- 

 Cassian Series, although of no great thickness. These cannot be 

 regarded as a determining factor in the subsequent crumpling, 

 shearing, and faulting of that soft and yielding series between the 

 Mendola Dolomite and the Schlern Dolomite of this region. 



^ The writer drew attention to this feature in a previous paper, when de- 

 scribing the analogy of the fault-systems of Enneberg with the Judicarian and 

 Asta systems of faults, demonstrated by the Austrian geologists in the Peri- 

 Adriatic region. ' No hard-and-fast distinction can be drawn between these 

 systems ; they pass into one another and form one complicated system of 

 movements, which may be proved even in the small district of Enneberg to 

 have affected the positions of both Triassic and Mesozoic rocks,' and therefore 

 to be of Tertiary age (' Coral in the Dolomites,' Geol. Mag. 1894, j). 55) 



2 This was my opinion before carrying out the additional research embodied 

 in the present paper. 



Q. J. G. S. No. 219. 2 p 



