Br. A. P. Young— Structure of the Tarntal Mass. 345 



serpentine schist and dolomite is now completely inverted, but whether 

 it is to be regarded as a simple overthrust mass or the lower limb of 

 a recumbent fold cannot be decided on the evidence. 



In the Mieselkopf occurrence the alternate plates of schist and 

 dolomite breccia ai'e parallel to the larger bands of dolomite seen on 

 the ridge, from which it appears that the earlier flows of magma were 

 guided by movements of the crust which coincided in direction with 

 the general movement to which the present structure is due. 



As regards the tectonic character, the mass of the Tai'ntal may be 

 divided into two parts. The massive Triassic dolomite with Rhsetic 

 and perhaps Liassic limestones in normal position forms the lower 

 part. This may be called the ' Knappenkuchel block'. The upper 

 part of the mass includes the serpentine, schist, and Tarntal breccia, 

 all probably older than the Trias and in inverted sequence. This 

 may be called the * Reckner block'. 



Where the two masses meet is a sheared band formed partly of 

 the upper beds of the lower block and in part of the lower beds 

 of the upper block, approximately bands 3 and 4 of the section on 

 p. 340.1 



The series on p. 340 and Fig. 9, p. 339, arranged in the original 

 sequence, would stand thus : 6 5 4 1 2 3, — 6 being lowest. 



Phtsiography. 



A conspicuous topographical feature of this mountain is the Griibl, 

 the great cirque already mentioned. It no doubt owes its present 

 form to ice erosion, by which the massive dolomite has been removed 

 down to the present floor of schists. Small knolls of schist at the 

 lip of the cirque show the well-rounded form of true roches 

 moutonnees. The ice-tongue of sufficient mass to mould these 

 knolls must have been fed by an extensive field of firn, and the 

 snow-line must have stood for a considerable time at a level above 

 the floor of the cirque, not lower probably than 2250 metres above 

 sea, or 100 metres above the present floor. Above this level the 

 available collecting area diminishes rapidly with the height ; at 

 2500 metres it still includes the whole feeding-ground of the Upper 

 and Lower Tarntal; 100 metres higher, at 2600 metres, little but 

 the slopes of the ridges would remain. It seems, then, probable that 

 the snow-limit at the period in question stood somewhere between 

 2250 and 2500 metres, or say at about 2400 metres. 



We have here evidence of a resting stage during an advance or 

 (more probably) a retreat of the ice. At the period of extreme 

 glaciation the snow-line could not have been higher than 1800 metres, 

 that is, it must have been at least 600 metres lower than the level 

 attained when the ' Griibl ' was excavated. 



The Lower Tarntal is a straight east and west groove, the erosion 

 of which must be due chiefly to running water. It has been beheaded 

 by the Lizumbach, and the flow of water is now insignificant. 



The Upper Tarntal is a basin-shaped hollow 80 metres above the 

 Lower Tarntal, and has also been truncated considerably on the 



1 This modifies somewhat the hypothesis {a) (p. 603 of last year's paper) offered 

 before the discovery of the Mieselkopf occurrence. 



