Mr. De la Beche 07i the Excavation of Valleys. 247 



The road that passes through it may be said to be notched and 

 tunnelled in its sides. This place presents us with two epochs. 

 1. That when some great catastrophe broke away portions of 

 the high Alps, with sufficient force to round the fragments, and 

 lodge them above the margin of the gorge, as well as at the 

 bottom of the ancient lake. 2. That in which the river has ex- 

 cavated the narrow gorge, cutting through the gravel and 

 through the rock beneath it. Fig. 3. will afford a general idea 

 of this celebrated spot; the height of the gorge being there 

 represented very considerably greater than its real proportion 

 to its length : a, o, the cross range cut through ; b, h, gorge 

 of the Via Mala, excavated by the Rhine ; c, c, c, bed of the 

 actual river, which has cut through the bed of the ancient lake 

 as well as the gorge; d,d, supposed surface of the ancient 

 lake; g, g, gi g, g, ancient gravel. It can I think be scarcely 

 doubted that this gorge has been formed by the river that now 

 rushes along it, and still continues its excavations. It has cut 

 below the ancient bed of the lake, as may be seen where the 

 gravel level has been destroyed and torn away at the higher 

 extremity of the gorge. 



The same violent cause which has lodged the gravel in the 

 higher parts of the Via Mala, has also deposited an immense 

 abundance of the same rolled fragments between Tusis and 

 Coire, which actual causes tend constantly to destroy and carry 

 away. The accumulation of mountain detritus produced by 

 actual meteoric influences upon this gravel is also seen on both 

 sides of Coire ; from different ravines the torrents throw out 

 daily upon the valley of the Rhine the disintegrated fragments 

 of the mountains, and these have arranged themselves in the 

 form of a talus at the bottom of each ravine upon the more 

 ancient gravel, in the same manner that sand poured through 

 a notch in a block of wood would arrange itself upon a table 

 on which the block rested ; — in this illustration the table re- 

 presents the ancient gravel ; the notch in the wood, the ra- 

 vine in the mountain ; and the sand, the modern detritus. This 

 ancient gravel, between the junction of the two Rhines and 

 Coire, is cut into cliffs and ravines, and undergoes daily dimi- 

 nution from actual causes. It contains laige blocks and boul- 

 ders, which would seem to refer the epoch of its Ibrmation to 

 that which scattered blocks from the Alps in all directions. 

 The gravel upon the higher part of the Via Mala is the same 

 as here mentioned, and is probably of the great block epoch, 

 and it must have been sub.sc'(|uent to this that the gorge itself 

 was cut out, gradually draining the lake behind it. 



The celebrated falls of Niagara afford an example of a river 



now 



