62 STRATIGEAPHICAL GEOLOGY 



become greenish from the development of augite or hornblende 

 crystals, which increase in size till the rock passes into amphibolite 

 or pyroxemite. By others, however, some of the phyllites are 

 considered to be of Brioverian age. 



2. Austria and Switzerland 



A long tract of crystalline rocks, some of which are probably 

 Archaean, extends from the Graian and Cottian Alps on the borders 

 of France and Italy through the southern part of Switzerland 

 (Pennine, Lepontine, and Rhaetian Alps), and is continued eastward 

 through the Tyrol into Carinthia and Styria. 



According to von Hauer's map of the Eastern Alps, the funda- 

 mental rock of that region is a group of banded hornblendic and 

 micaceous gneisses, which he terms " the Central Gneiss " ; outside 

 this is a series of micaceous schists, followed by a formation called 

 the Thonschiefer, i.e. silvery or sheeny schists. 



The gneisses of the " Central " group are only occasionally exposed 

 along the central axis of the chain. Those of the Velber-Tauern 

 Pass and the neighbouring Gross Venediger are thus described by 

 Professor Bonney : 82 " These, whether micaceous or hornblendic, 

 recalled to my mind certain members, but not the most coarsely 

 crystalline, of the Hebridean of Scotland and the Lauren tian of 

 Canada, which are often distinctly modified by subsequent pressure. 

 We also find slightly foliated, coarsely crystalline, granitoid rock 

 with nodes or enclosures, probably a granite subsequently modified, 

 the upper part of the mountain chiefly consisting of the latter 

 rock." The Gross Venediger rises to a height of 12,000 feet. 



Overlying these gneisses and apparently passing down into them 

 is a series of fine-grained gneisses and mica-schists, often distinctly 

 banded with white (quartzose) and dark (biotitic) layers, and this 

 bedding-foliation is often modified by a subsequent cleavage- 

 foliation. With these rocks are associated bands of porphyritic 

 gneiss which Professor Bonney regards as igneous rocks intruded 

 into them before the production of the earlier foliation. 



The Thonschiefer Series is a well-defined group of rocks which 

 extends throughout the Eastern Alps from the Swiss border nearly 

 as far as Gratz. It consists mainly of leaden-coloured micaceous 

 schists which have glistening sheeny surfaces, but it includes bands 

 of a more quartzose schist with some of calc-schist and crystalline 

 limestone. 



Again, in the Western Alps of France, Italy, and Switzerland, 

 Professors Bonney, Gastaldi, and others have recognised a similar 

 succession of (1) coarse banded gneisses apparently succeeded by 



