1821.] and odjoining Parts of the Continent. 455 



with the magnesian limestone that rests in the coed formation of 

 England, and characterised by containing gypsum, salt and 

 metallic ores, and occasionally beds of saliferous marl, red sand- 

 stone, and rouhwacke ; the latter entirely destitute of all these 

 substances, and comprehending beds which their organic 

 remains and superposition to the elder alpine limestone and 

 occasional structure show to be contemporaneous with the lias 

 and oolite, and sometimes green sand and chalk formations of 

 England. The chalk seems to occur only on the Italian side of 

 the Alps, near Vicenza. 



These beds of alpine limestone are bounded externally by the 

 Tertiary formations of the Plain of Lombardy on the south ; and 

 by similar tertiary formations in the Great Valleys of the Danube, 

 and of Geneva on the north. 



Internally, they are terminated by two precipitous escarp- 

 ments; one on each side of, and both rising towards, the centraL 

 primitive ridge. 



Betv/een these two escarpments there are detached ridges 

 and insulated or outlying masses of the same alpine limestone 

 covering occasionally large tracts of the intermediate primitive 

 country. 



'Note. — The great north escarpment produces a remarkable 

 effect upon the upper courses of all the important rivers that 

 rise on the north side of the central watershed of the Alps, i. e. 

 the Iserre, Rhone, Rhine, Inn, Salza, andEnns. 



Most of their tributary streams take origin in the central pri- 

 mitive ridge, and descend northwards till they meet the great 

 escarpment of the alpine hmestones. On approaching this, they 

 are suddenly deflected nearly at right angles to their former 

 direction, and run under it from 50 to 100 miles, till some gorge 

 or fracture in the limestone allows them to escape into the plains. 



The above rivers enter their gorges at the following places : 

 The Iserre at Grenoble. Rhone at St. Maurice. Rhine at 

 Sargans. Inn above Kufstein. Salza at Werfen. Enns at 

 Hiflau, 10 miles north of Eisenertz, in Styria. 



The extent of their course under the escarpment is as follows: 



Iserre from Confians to Grenoble. 



Rhone from the Furka to St. Maurice. 



Vorder Rhine from its source to Coire. 



Inn from Landek to Inspruck and Kufstein. 



The course of the Upper Salza is not in the valley immediately 

 subjacent to the limestone escarpment, but in a parallel valley 

 of primitive rocks at no great distance to the south of it. 



Some minor rivers between this valley and the escarpment are 

 similarly affected by it, and escape by minor gorges. 



Enns from Radstadt to Hiflau. 



The south calcareous belt appears to dip (at least at its west 

 extremity near Como and Verona) towards the plain of Lorn- 



