190 Reports and Proceedings — Edinburgh Geological Society. 



the Tertiary crust movements in the Alps this passage zone had 

 been the great crush-zone of the district. It occurred in Fassa 

 below a massive development of calcareous rocks, and above an 

 almost equal thickness of mixed deposits ; it was therefore a well- 

 marled ' critical ' zone within the earth's crust, interleaved between 

 rock material, presenting strongly contrasted physical characters. 

 The maximum deformational effects had been attained at this zone, 

 and in the other leading ' critical ' zone presented by the Wengen- 

 Cassian marls. Innumerable planes of overthrust and downslip had 

 developed within these bands, some with only 10 degs. to 20 degs. 

 inclination, others much steeper. Vast eruptions of molten rock 

 had found their way into these deformational zones, and con- 

 solidated in the form of wide sheets and sills at those definite 

 horizons within the Triassic succession. Thus, one of the general 

 results of her detailed survey had been to disprove the previous 

 conception that the porphyrite rocks in Fassa had originated as 

 surface outflows in Triassic time, and to show that they had been 

 intruded into the local fault lines and planes of crust deformation 

 which developed during middle and late Tertiary Alpine move- 

 ments. A similar result had been obtained several years ago by her 

 for the area on the north. The previous investigators had failed to 

 recognize the presence of the innumerable crust planes with 

 extremely low inclination, and consequently overlooked the corre- 

 lation of the igneous invasions with pre-existent deformational 

 structures. After indicating on the map the complete sequence of 

 the igneous rocks at Monzoni, Mrs. Gordon proceeded to describe 

 her new results regarding cross-fold formation. Several folding 

 movements had affected this district. In the first place, undulations 

 directed east and west had formed with a steep southern face and 

 a long northern slope, the width of an undulation being about 

 4|^ miles. These had been deformed by oblique cross-folds, which 

 developed simultaneously along two directions, E.N.E.-W.S.W. and 

 W.N.W.-E.S.E. During these movements the steep south faces of 

 the original plications were overthrust towards S.S.E. and S.S.W., 

 and the first inrush of molten rock occurred into zones of crust 

 attenuation and fracture. Still later, another duplex system of 

 cross-folds was superinduced rectangularly upon the earlier in 

 N.N.W.-S.S.E. and N.N.E.-S.S.W. directions. Overthrusts and 

 shear-slips took place again, and fragmented the previous thrust 

 masses and igneous intrusions. Mrs. Gordon showed by reference 

 to her map that the most intense effects of crust deformation had 

 been coeval with this advanced stage in the superposition of duplex 

 deformational systems upon the original and fundamental east- west 

 undulations. A subsequent epoch of crust adjustment and surface 

 erosion had ensued, characterized by local subsidences taking place 

 pre-eminently along the previous crust fractures. Local crumplings 

 had then occurred around large masses of igneous rock or the larger 

 deformation fragments of Triassic limestone. Small igneous inter- 

 calations of highly differentiated rock materials accompanied these 

 inthrows. Mrs. Gordon's interpretation of this remarkable series of 

 cross-folds was based upon the principle of the simultaneous action 



