A. V. Jennings — The Landwasser and Landquart. 259 



imtnecliately covering grits, was at that time undergoing denudation. 

 The Labrador volcanic breccias, as they have been called, bear 

 witness to the fact that during their accumulation the covering grits 

 were being largely demolished, the granite sparingly, if at all. Now, 

 assuming these breccias to be Permian, would it not be possible to 

 trace the gradual uncovering of the Western granites by the character 

 of the debris found throughout the newer beds of the Eed Sand- 

 stones? A very arduous task, no doubt, but an interesting one. 

 Then the schorlaceous rocks of such distant localities as Teignmouth, 

 Budleigh Salterton, and the Midlands, should be carefully compared. 

 Perhaps the first question to get answered is — Is there any region 

 known, except the West of England, which produces crystalline 

 schorlaceous rocks crammed with chlorides ; and fine grits, saturated, 

 so to speak, with tourmaline ? 



I need not say what a very important bearing these tourmalinized 

 grits have on the volcanic theory of Dartmoor. Were the Dartmoor 

 rocks first exposed to denudation, the once plutonic tourmalinized 

 grits ; or were they the higher lavas and ashes of a volcano ? They 

 cannot very well have been both. Then how are we to reconcile the 

 apparently early appearance of these covering grits in the con- 

 glomerates with the famous Cattledown hypersthene-andesites found 

 by the late Mr. R. N. Worth, and referred by him to an ancient 

 Dartmoor volcano ? Dartmoor is a wondrous easy problem if we 

 suppress inconvenient evidence. But hear all sides, and it is a tough 

 nut to crack. 



In conclusion, I cannot refrain from expressing my admiration of 

 the pertinacity with which my friends, Messrs. Somervail and Lowe, 

 have so continuously attacked the Culm conglomerates. These 

 granitic fragments are entirely new facts, and facts which may lead 

 to a good many more, and one real new fact about Dartmoor is worth 

 a volume of theories, however large such volume may be. 



V. — On the Courses of the Landwasser and the Landquart. 

 By A. Vaughan Jennings, F.L.S., F.G.S. 



CASES of relatively recent change in the courses of rivers, due to 

 the invasion of their valleys by neighbouring and more rapidly 

 working streams and the consequent diversion of their waters, have 

 been investigated of late years by an increasing number of geologists 

 in different countries. Such phenomena are, of course, most frequent 

 in mountain districts, and the Swiss Alps have yielded many 

 examples of greater or less certainty. Some cases are evident and 

 undeniable ; others are difficult to decide upon, and need careful 

 consideration of all available evidence ; while in yet other instances 

 it is possible that statements as to the occurrence of such changes 

 have been accepted on inadequate authority. The generally received 

 opinion as to the present and past relationship of the Landwasser 

 and the Landquart can certainly not be included in the last category, 

 but neither can it, I think, be rightly placed in the first. 



The Landquart is a river of Northern Graubunden which now 

 :flows from the glaciers of the Silvretta group northward and 



