194 GLACIAL HISTORY. 



an inroad into the basin of the Lake of the Four Cantons,, and 

 thence gradually covered the Canton of Lucerne with a bed of 

 ice, whilst the right branch, after uniting with the glacier of the 

 Muottathal, advanced between the Righi and the Rossberg to the 

 Canton of Zug, and thence spread over the districts of Freiamt 

 and Aifoltern. The two branches probably united again to the 

 north of the Righi. A great central moraine brought down in- 

 numerable blocks of the St.-Gothard (Geissberg) granite, which 

 cover the mountain-terraces above the lake of Uri (as, for in- 

 stance, near Seelisberg and Morschach), and are scattered over 

 the Cantons of Lucerne and Argovia and the district of Affol- 

 tern. A lateral moraine carried down immense masses of lime- 

 stone, which extend high up on Mont Pilate, and which form 

 near Hergottswald an enormous rampart cut through by moun- 

 tain-streams. At the time of its greatest extension the glacier 

 of the Reuss reached to the chain of the Albis, and stretched its 

 branches through the Schnabel pass and the Mutschelle into the 

 region of the Limmat, carrying over the same St.-Gothard gra- 

 nite. The fine terminal moraines of the Cantons of Argovia 

 and Lucerne, which have already been mentioned (p. 178), indi- 

 cate a time when the glacier terminated in that region. 



Between the glaciers of the Reuss and the Aar, and the ter- 

 minal moraine of the Rhone basin, there was, at the period of 

 the greatest extension *of the glaciers, a small island stretching 

 from the district of the Napf to the Aar, which remained un- 

 covered by ice, and possesses no trace of erratic boulders in any 

 part of its formation. 



The glacier of the Linth received its principal supply from 

 the Canton of Glaris, although a vast glacier must have come 

 through the valley of the Wallensee to unite with the Linth 

 glacier near Wesen. The whole then advanced through the 

 Gaster and March, towards the basin of the Lake of Zurich. It 

 covered a great part of the Canton of Zurich with a thick icy 

 mantle, which, at the time of its greatest extension, reached the 

 Bachtel, and on the other side extended to the ridge of the 

 Uetlibcrg. At that time its surface was loaded with several 

 moraines, one of which started from the Glamisch, the Rauti, 

 and the mountains bordering the Linth valley, and brought the 

 limestones of those high regions to the Canton of Zurich, where 



