74 



PHYSICAL GEOLOGY 



Fig. 52. — Landslide, Turtle Mountain, Alberta. 

 (Photo. Hopkins.) 



along a plane of 

 steeply dipping slate 

 which had been lubri- 

 cated by underground 

 water. 



In mountainous re- 

 gions, where the val- 

 leys are deep and the 

 slopes steep, condi- 

 tions are extremely 

 favorable for land- 

 slides (Figs. 51, 52). 

 One of the most de- 

 structive of such slides 

 occurred on the Ross- 

 berg in Switzerland 

 in 1806. Here the rocks high up on the mountain slid suddenly into 

 the valley, burying the village of Goldau and causing the death of 

 several hundred people. Masses of rock, some of which were as 

 large as houses, were spread over the valley for two or three miles. 

 Evidences of many prehistoric landslides are to be seen in Switzer- 

 land, as well as in other mountainous regions. At Siders a land- 

 slide is spread out for several miles across the Rhone valley, and 

 some of the hills formed from the material of the slide are almost 

 200 feet high. So 

 marked is this land- 

 slide topography that 

 it forms the boundary 

 between the French 

 and German-speak- 

 ing people in the 

 Rhone valley. 



Conditions favor- 

 able for landslides 

 were created artifici- 

 ally in the excavation 

 of the Culebra Cut 



in the Panama Canal, 



l , 1-11 ' H; - 53- — A lake in eastern Trance formed by a 



Where the rock will landslide< The character of the material of the dam is 



Continue tO slide peri- shown in the foreground. 



