24'6 Mr. De la Beche on the Excavation of Vallet/s. 



The celebi'ated Rheingau may perhaps also be cited as art 

 example of a gorge having drained a mass of waters behind it; 

 for if closed, a lake would be formed over the plains of the 

 Rhine back thence towards Basle. 



These appearances are not confined to one partof the world ; 

 it is very easy to see from the descriptions of intelligent tra- 

 vellers, that they exist voy commonly: I have myself observed 

 examples in Jamaica. The district named St. Thomas in the 

 Vale is a marked one : here we have low land bounded on all 

 sides by hills which would form the banks of a lake, were 

 not the waters let out by the gorge through which the Rio 

 Cobre flows. Luidas Vale, in the same island, is a district sur- 

 rounded on all sides by high land, and would form a lake, were 

 not the waters, derived from heavy tropical rains, carried off* 

 by sink-holes in the low grounds. In consequence of this escape 

 of the waters a lake cannot be formed, and therefore no dis- 

 charging river, which should deliver the excess of waters over 

 the lowest lip of the high land. This vale therefore presents 

 ho such gorge as woukl have resulted from the cutting power 

 of a draining river, such as has taken place at St. Thomas in 

 the Vale. 



It is needless at present to attempt a further enumeration 

 of these appearances ; they will readily present themselves to 

 the minds of those who have attentively examined any large 

 district, particularly a mountainous district : but the famous 

 gorge of the Via Mala in the Grisons is too striking an ex- 

 ample to be omitted. 



The valley of Domleschg, at the upper part of which stands 

 Tusis, is separated from that of Schams by a lower cross range 

 of mountain, which would bar the progress of the Rhine down 

 the valley, and convert the valley of Schams into a lake, were 

 it not for the opening of the Via Mala, which has been cut 

 through the cross range. 



Upon entering the gorge of the Via Mala, ancient rounded 

 gravel will be observed to compose the upper part of the cliff' 

 and to rest upon soft gray schist. It seems not to have been 

 formed, but to have been cut through by the causes that exca- 

 vated the gorge. The same gravel forms terraces in the val- 

 ley of Schams, also cut through at the upper exti'emity of the 

 Via Mala. As we descend the gorge it will be observed in 

 many places high above the river, reposing on the schist. 

 The gorge itself is of considerable length, its general breadth 

 from fifty to seventy yards, and its depth several hundred feet. 



of a lake, tlic ilrainagc of which was effected by a cut tliroiigh the high 

 land that hounds it on the west. It' this ontlet were closed, the waters of 

 the Anio would niiain cover the iilaia and convert it into the bed of a lake. 



The 



