582 MISS M. M. OGILVIE [mKS. GORDON] OS THE [Aug. I 899, 



separating the Groden Pass area from the Pralongia and St, Cassian area. The 

 fault runs in a north-north-westerly and south-south-easterly direction, but a 

 bi'aneh crosses the Pass north and south towards Crap di Sella. These three 

 faults afterwards furcate to south-south-west. Still two other faults occur 

 farther east — one, the north-north-west and south-south-east fault at St. Cassian ; 

 the other, the north-and-south fault which cuts oiF the Groden Pass Anticline 

 finally against the Centurinus group. 



8. Correlation in form and structure between the anticline 

 and the adjacent synclinal areas. — The diagonal faults of the Groden 

 Pass and their furcations sweep closely round, or pass into, the Dolomite- 

 massives occupying the synclinal areas north and south of the Groden Pass 

 anticline. The geological map (PL XL) shows that the diagonal torsion-faults 

 in springing across and away from the anticlinal buckle permitted the virgating 

 fault-blocks to be twisted away from the directions of strike into increasingly 

 oblique directions. The various oblique positions assumed by such torsion- 

 offshoots from the Pass anticline have determined the boundaries of the synclinal 

 areas immediately adjacent to the Pass. 



Hence torsion-faulting is the basis of the correlation in form which obtains 

 between the convex curves of the anticline and those of the adjacent Dolomite- 

 massives. There is also a correlation in structure, since the opposite synclinal 

 regions behind the main overthrusts and return overthrusts of the Pass anticline 

 are clearly opposite regions of rock-distension, correlated with the Pass area 

 of strong compression and even dovetailing of crust-folds. In the peripheral 

 parts of the massives which immediately adjoin the anticline the rocks have 

 undergone a thrust towards the anticline ; while in the internal parts, remote 

 from the anticline, the rocks have subsided into deep troughs. 



A certain reciprocity of structure may be noted between individual synclinal 

 basins on opposite sides of the anticline. It will be remembered that the 

 synclines diagonally opposite each other have undergone the same direction of 

 spiral twist. Thus the Spitz Kofl and Tschampatsch groups in the Gardenazza 

 Massive are the reciprocals of the Pitz Kofi and Meisules groups in the Sella 

 Massive. Again, a structural correlation has been indicated between the deep 

 synclines of the Lang Kofi and Sass Songe mountains at diagonally opposite 

 curves ; and a correlation also exists between the shallow synclines of the 

 Sta. Maria-Wolkenstein and the Pralongia meadows placed diagonally opposite 

 each other at the north-western and south-eastern curves of the ellipsoid. 



9. Torsion-figures. — Oblique fault-angles are formed (a) when a 

 diagonal fault directed north-north-east and south-south-west useets or intersects 

 a diagonal fault directed north- north-west and south-south-east ; (b) when a 

 north-and-south fault meets or intersects any diagonal fault ; (c) in various 

 cases of oblique intersection between longitudinal and cross-faults. The several 

 possibilities o. coincidence and intersection can be verified in the accompanying 

 map (PL XL), together with the consequent formation of distorted lozenge- 

 shaped and polygonal figures. 



Meantime, attention is simply called to such as occur in the Groden Pass. 

 The two limiting-faults AB' & A'B (fig. 7, p. 578) form an X shape, with elon- 

 gated centre, disposed east and west across the Pass, while the areas between the 

 arms of the X are laid out in long-sided V and W figures, with the intervention 

 of small triangular wedges at sharp torsion-curves. These forms are similar 

 to the characteristic torsion-fi'gures which were obtained experimentally by 

 Daubree. 



The chief joints and the cleavage-planes have the same oblique and inter- 

 secting directions as the diagonal faults, and, like the latter, these finer planes 

 of rupture veer round to directions parallel with the curving strike of the 

 Pass folds. In short, the present author's observations go to show that the 

 torsion -figures, evident on a large scale in the general structure of the Pass, 

 are equally demonstrable in the cleavage-phenomena of the rocks. 



10. Superposition of the torsion-phenomena upon pre- 

 existing crust-folds. — The intimate association of the longitudinal bundles 

 of faults and the furcating diagonal or transverse faults is unmistakable. 

 Not only do fault-dykes pass uninterruptedly from one to the other, but also 

 the stratigraphy on the opposite sides of a diagonal fault shows that the 



