Vol. 55.] THE TOESION-STKUCTURE OF THE DOLOMITES. 631 



The identity in the tectonic character of the adjacent neighbour- 

 hoods is unmistakable ; and if torsion can be applied correctly as 

 an explanation of these features in Enneberg, there is every reason 

 to suppose that it can be applied for the whole area. 



Age of acute torsion. — The Judicarian or north-north-east 

 and south-south-west system of folds and faults in the adjacent 

 neighbourhood affects the whole series of rocks, from Permian to 

 Middle Tertiary. Hence the oldest period which can be adduced for 

 the acute stage of torsion and the injection of the eruptive rocks 

 along the chief torsion fault-lines and curves is Middle Tertiary. 



In a word, the outbreak of the more acid series of 

 eruptive rocks in Southern Tyrol marked an advanced 

 phase in the phenomena of strike - torsion in that 

 region, and was associated with an important system of 

 diagonal and transverse faults, some of which in all 

 probability still act as planes of lateral displacement 

 and crust-adjustment. 



It is worthy, of remark, that the recurrences of eruptive activity in 

 Southern Tyrol would thus be proved to have been always associated 

 with great crust-movements: (1) those of Permian uprise and 

 mountain-making; (2) those of Triassic depression; (3) those 

 of Tertiary torsion and mountain-making, inducing and followed 

 by local subsidences. 



During the period of torsional uprise, the eruptive activity 

 chiefly took the form of central bosses and laccolithic expansions 

 in the characteristic crust-buckles, and was accompanied by fault- 

 dykes and sills. During the subsequent period of local depression 

 the activity has largely taken the form of superficial flows and 

 volcanic outbursts. 



It is just possible that some of the interrupted north-and-south 

 lines of fault in the Judicarian-Asta region (fig. 22, p. 630), as well as 

 the north-and-south exposures of Permian eruptive rocks, in which 

 again Tertiary rocks burst through, may correspond in position to 

 ancient transverse lines and valleys in the pre-Permian and Permian 

 Alps. This seems especially worthy of attention in the occurrence 

 of the Tertiary rocks in the Vicentine area, Asta, and Fleims-Fassa 

 centres. These areas occur along a north-and-south line, and in 

 each case the eruptions are associated with outcrops of old schist- 

 rocks or of older eruptive rocks. In Scotland, it has been proved 

 that fresh outbreaks of eruptive rocks in many cases followed old 

 valleys.^ 



Peri-Adriatic torsion-curves. — The sketch-map of the 

 Judicarian-Asta area given by Suess - has been taken by the 

 present author as the basis of a new diagram (tig. 22). Torsion- 

 curves have been drawn through the area in accordance with the 

 principles laid down in the present paper. Generally considered, it 

 depicts a region folded in one geological age along east-and-west 



1 A. Geikie, ' Anc. Vole. Gr. Brit.' vol. ii (1897) pp. 61, 65, 96. 



2 ' AntUtz der Brde,' vol. i (1885) p. 322. 



