SUMMIT LEVELS AMONG ALPINE MOUNTAINS 121 



lack of a commonly used English equivalent for the German word 

 Felsenmeer. Equally striking is the fact that very few physiographic 

 textbooks even mention one of the most characteristic and widely 

 exemplified features of alpine mountains. Frost-action is, of course, 

 chiefly responsible for the wonderful chaos of broken rock above 

 tree-line. The Felsenmeer is itself direct evidence of exceptionally 

 rapid disintegration. At many points the blocks of the rock-chaos 

 are in special danger of being swept away by avalanches, or of more 

 slowly moving valleywards by the powerful thrusting action of 

 freezing water. The development of the Felsenmeer means a vast 

 increase of rock surface on which frost, changes of temperature, and 

 all the other chief methods of weathering, and therewith destruction, 

 can act. Below tree-line an all-mantling Felsenmeer, because of the 

 forest blanket, is forbidden. Much of the broken rock below tree- 

 line is exotic, having fallen from the treeless zone. The indigenous 

 Felsenmeer below the tree-line is chiefly concentrated beneath cliffs, 

 and is a vanishing quantity when compared with the immense rock- 

 chaos above. Both as an evidence of incomparably more rapid 

 frost attack above tree-line than below, and as a condition for more 

 effective attack by agents other than frost, the Felsenmeer is significant. 

 b) Removal of rock-waste. — On the other hand, the streaming of 

 weathered material down the slopes is, other things being equal, 

 probably several times more rapid in the treeless zone than below it. 



(1) The direct beat and wash 0} the rain have practically negli- 

 gible effect on waste-removal below tree-line. The power of heavy 

 rain washing the treeless zone, either in the derived form of rills or 

 as a sheet flood, is manifest to anyone who has experienced a good 

 shower above tree-line. 



(2) During the last two field-seasons the writer has for the first 

 time become conscious of the importance of burrowing mammals in 

 preparing loose rock-waste for speedy transit to the valleys. In the 

 western Cordillera field-mice, gophers, moles., marmots, bears, and 

 other species are each year doing an immense geological work. 

 There can be no exaggeration in saying that these burrowers annu- 

 ally turn over hundreds of thousands, if not millions, of tons of soil 

 or disintegrated rock in either the Coast Range or the Selkirk Range 

 of British Columbia. Such work is of relatively little importance 



