Dr. M, M. Ogilvie Gordon — Monzoni and Tipper Fassa. 313 



E.N.E. strike and northward dip of the whole mass. In succession 

 from south to north the zones are : (a) the lowest zone, a light 

 coarse-grained monzonite specially rich in mica ; (b) a finer-grained 

 differentiation of the micaceous type of monzonite : (c) a coarse- 

 grained, pyrosenic, or gabbro-like monzonite ; (d) a finer-grained 

 dark type, highly augitic ; this uppermost zone sends short apophyses 

 into the limestone of the peripheral zone. 



Differential movements subsequent to the 'Asta' injection of 

 monzonite have concentrated themselves at the zone between the 

 finer-grained micaceous type and the coarse gabbro-like monzonite. 

 The dip-joints curve steeply northward at this horizon, and the 

 auffitic se2:reo:ation zones have been downthrown to the north and 

 west and sliced by several shear-planes both in strike and cross 

 <lirections. The chief fault-zone runs entirely through the Monzoni 

 mountain, following a curved strike, which, like the Judicarian-Asta 

 fault-system round Allochet and Campagnazza, is convex to the north. 

 The fault-zone through Monzoni is parallel with the peripheral fault- 

 system, limiting Monzoni on the west, north, and east. In the 

 fault-zone the monzonite rock is sheared and slickensided in the 

 very highest degree, having been converted into a monzonite fault- 

 schist, or in some places into a coarser fault-breccia. Moreover, the 

 fault-zone is the seat of later injections, in contact with which the 

 earlier gneissose bands of monzonite have endured extreme contact 

 alteration. The later injections have two very important tectonic 

 features in common with the porphyrite sill and dyke system of the 

 Campagnazza. They extend continuously in the strike fault-curve 

 through Monzoni, and in numerous cross-faults (N.N.W., N.S., and 

 N.N.E.) which cut Monzoni into a series of cross- segments com- 

 parable with those of the Campagnazza. This feature in itself gives 

 a safe indication that the later injections in Monzoni were, like the 

 porphyrite sills in the Campagnazza, associated with the ' Judicarian' 

 movement. But there is still stronger evidence. The whole of 

 Monzoni has been cross-cleaved, the strike-cleavage being north- 

 east to south-west, and the slabs of dip-cleavage being inclined to 

 the south-east. The cross -cleavage planes of Monzoni are in 

 fact a repetition of those displayed in the stratified rocks of the 

 Campagnazza, and the differential correlative planes are similarly 

 developed. The later injections in Monzoni ascend pre-eminently 

 the vertical cross-cleavage planes or the inclined planes dipping 

 south-east. Thus it may be safely concluded that the later irruptions 

 in Monzoni took place in the Miocene epoch when the Asta-Judicarian 

 movements had reached their most intense phase in the Alps. 



The series of later injections includes a much greater mineralogical 

 variety of igneous types than the earlier intrusion. The first in- 

 jections of the later series include somewhat abnormal augitic and 

 hornblendic types of monzonite and a still more basic olivine-gabbro 

 type, coarsely ci'ystalline for the most part, but passing into basaltic 

 facies. This rock is readily recognized in the leading fault-zone 

 by its chai'acteristic ferruginous and serpentinous decomposition 

 products. It also runs northward as cross-dykes in the rugged 



