570 MISS M. M. OGILVIE [mRS. GOKDON] ON THE [Aug. 1 899, 



Mendola Dolomite, and of the next higher or 'Buchenstein' (see foot- 

 note, p. 569) horizon of limestones. An important dyke is exposed 

 on the northern slopes of the Vallbach hill and in the bed of the 

 stream. It marks a fanlt-line which penetrates the northern half 

 of the anticline and lets down the Wengen strata to the north, just 

 as the fault of the Pitzculatsch hill cuts the southern half and effects 

 the downthrow of the Wengen strata to the south. These two faults 

 are distinguished as A & B in the section (fig. 1, p. 568), and may 

 be conveniently termed the Pitzculatsch and Vallbach Faults 

 respectively. 



Another intrusion on the summit and southern slope of theVallbacli 

 hill presents a connected 'torsion-network' (Lessen) of dykes 

 and sills, threaded through the Muschelkalk and Lower Trias in 

 fault-plaues inclined northward at various angles, and sometimes 

 vertical (fig. 1, p. 568). The Vallbach intrusions occur in con- 

 nexion with a series of faults that penetrate the northern wing of 

 the anticline, and effect torsion of its strike round the dolomite- 

 cliffs north of the Pass. 1 followed this network in all its detail, 

 ascending the precipitous rocks facing the church of Sta. Maria, 

 and discovering there very good examples of shear-and-contact 

 metamorphism in horizons of Muschelkalk ; then tracing the various 

 threads round the slopes facing Plon and along the ridge of the 

 Vallbach hill between the Vail and Frea streams. Altered and 

 brecciated Muschelkalk-rocks in the form of the so-called ' Buchen- 

 stein agglomerate' accompany everywhere the igneous intrusions. 

 It is quite impossible to show all the details in the map (PI. XL)^ 

 yet it is hoped that sufficient detail is there given to prove that 

 the injection of igneous material has taken place in 

 a fault-network associated with an actual twist in 

 the strike of the rocks. 



First in importance in this map I rank the demonstration that 

 it gives of the intrusive rock running into and along the sub- 

 ordinate oblique and transverse faults on the Groden 

 Pass slopes, as well as into and along the main longitudinal, 

 inclined planes of fault. The intrusive rock extends for a 

 considerable distance in a north-and- south transverse fault between 

 Wolkenstein and the Pass. This may be termed the Wo Ik en- 

 stein Fault, and it is one of the chief transverse faults of the 

 district. 



Fresh specimens of the intruded rock may be described as some- 

 times typical porphyrite of the district with augitic crystals, some- 

 times a plagioclase-porphyrite ; amygdaloidal inclusions are frequent. 

 What have hitherto been grouped as ' Buchenstein tuffs,' and attri- 

 buted along with the augite-porphyrite to Middle Triassic age, are 

 fault-rocks representing a compounded mass of fault-dyke material 

 and fragments of the various stratified rocks affected in the planes 

 of crust-movement. Slickenside appearances are very prevalent, 

 while cleavage is another marked feature, extremely variable in the 

 rocks nearest the siUs and dykes. 



The 'fold-form' of the western slope of the Groden Pass (figs. 2 & 3, 



