314 Dr. M. M. Ogilvie Gordon — Monzoni and Tipper Fasm. 



spurs that descend to the Monzoni Alpe. Certain peripheral dykes 

 of very basic types of monzonite are also of this period. 



The next set of injections show marked differentiation into granitic 

 and augitic varieties. Usually the injections are found in group 

 form, the more acid and more basic types occurring together or 

 within a few yards of one another. Dyke-pairs of granite and 

 porphyrite or of monzonite aplite and hornblendic monzonite are 

 very common, and there are fault-dykes of aplite, pegmatite, or 

 highly felspathic monzonite. Seams of orthoclastic rock are freely 

 injected both in strike and cross directions. Those groups, pairs, 

 or seams of smaller dykes occur across the olivine-gabbro and normal 

 monzonite rocks in Monzoni, and also sporadically at the peripheral 

 shear and contact-zone, where they are very often associated with 

 a fine-grained basic porphyrite that weathers greenish, and answers 

 in its thinner threads to the description of the igneous rock which 

 has passed in the literature under the name of ' pietra verde.' 



The last injections include liebenerite porphyry, plagioclastic 

 porphyrite, and some ultrabasic limburgite types. Their occurrence 

 in the field is in north-south direction or very few degrees east or 

 west of this direction. They cross all other dykes ; several excellent 

 exposures that I found prove them to be the youngest type of 

 injected rock in Monzoni. They mark certain ' focal areas ' within 

 the mountain where strike and cross faults intersect. At these areas 

 local inthrows have occurred in relation to a cross-movement from 

 east to west, whereby cross-slices of Monzoni were overthrust 

 westward, and behind each thrust-slice there was a zone of downslip 

 and inthrow. 



The western thrust-slices present an arrangement of gneissose 

 bands following strike-curves convex to the west. This strike-curve 

 is orthogonal to the strike-curve convex to the south, which is 

 characteristic of the front portions of the Pellegrino and other 

 thrust-masses overthrust to the S.S.E. The focal areas around which 

 these transverse or 'Judicarian' strike-curves are arranged occur 

 within Monzoni, but the focal area corresponding to the general 

 strike-curve of the monzonite rocks is immediately north of Monzoni, 

 at an area in Monzoni Alpe where inthrow has taken place, and 

 where the N.N.E., N.S., and N.N.W. cross-faults that radiate 

 through Monzoni converge. 



I regard the olivine-gabbro and contemporary basic types of 

 monzonite in Monzoni as the deeper-seated facies of the massive 

 porphyrite sills that spread through the Triassic horizons in the 

 neighbouring districts ; whereas the granites, aplites, and the more 

 segregated types of porphyrite and monzonite in Monzoni were 

 coeval with certain fine-grained basic injections into the porphyrite 

 sills of the vicinity. 



The occasional ultrabasic dykes in north-south cleavage-planes 

 were still later. In Monzoni, in the neighbourhood of the chief 

 shear-zone, the rocks have been rippled along an east-west strike ; 

 in the Allochet ridge east of Monzoni there is rippling in this 

 direction, and cross-rippling due north and south. The wave-length 



