ICE AND GLACIERS. 101 



glacier are heaped up and form immense walls ; these are called 

 the lateral and terminal moraine of the glacier. Other heaps 

 of rock, the central moraine, stretch along the surface of the 

 glacier in the direction of its length, forming long regular dark 

 lines. These always start from the places where two glacier 

 streams coincide and unite. The central moraines are in such 

 places to be regarded as the continuations of the united lateral 

 moraines of the two glaciers. 



The formation f the central moraine is well represented in 

 the view above given of the Unteraar Glacier (Fig. 13). In 

 the background are seen the two glacier currents emerging from 

 different valleys ; on the right from the Schreckhorn, and on 

 the left from the Finsteraarhorn. From the place where they 

 unite the rocky wall occupying the middle of the picture de- 

 scends, constituting the central moraine. On the left are- seen 

 individual large masses of rock resting on pillars of ice, which 

 are known as glacier tables. 



To exemplify these circumstances still further, I lay before 

 you in Fig. 14 a map of the Mer de Glace of Chamouni, copied 

 from that of Forbes. 



The Mer de Glace in size is well known as the largest glacier 

 in Switzerland, although in length it is exceeded by the Aletsch 

 Glacier. It is formed from the snow-fields that cover the 

 heights directly north of Mont Blanc, several of which, as the 

 Grande Jorasse, the Aiguille Yerte (a, Figs. 14 and 15), the 

 Aiguille du Geant (b), Aiguille du Midi (c), and the Aiguille 

 du Dru (d), are only 2,000 to 3,000 feet below that king of the 

 European mountains. The snow-fields which lie on the slopes 

 and in the basins between these mountains collect in three prin- 

 cipal currents, the Glacier du Geant, Glacier de Lechaud, and 

 Glacier du Talefre, which, ultimately united as represented 

 in the map, form the Mer de Glace; this stretches as an ice- 

 current 2,600 to 3,000 feet in breadth down into the valley 

 of Chamouni, where a powerful stream, the Arveyron, bursts 

 from its lower end at k, and plunges into the Arve. The low- 

 est precipice of the Mer de Glace, which is visible from the 

 valley of Chamouni, and forms a large cascade of ice, is com- 



SANTA BARBARA 



