408 



H. II. East all Sf Bernard Smith— 



At its xipper end the tarn is being gradually filled up in the usual 

 manner by stream deltas, but since the gathering-grountl is so small 

 this must naturally be a slow process. It seems to be much 

 assisted by vegetation, which is more luxuriant than might be 

 expected at such an elevation. 



Turning now to a consideration of the outlet, we find several 

 interesting features. No rock is found in siiil at or near water- 

 level ; it is only at some distance down the stream that we first 

 observed any unmistakable rock in place ; this is at least seven or 

 eight feet below the surface of the lake. The narrow outflow valley 

 is filled with rounded mounds, which are very suggestive of 

 moraines, although they oontaiu a good many angular blocks. 



r^' 



Fig. 3.— Outlet of Blackbeck Tarn. 



A, C, old gorges ; E, large boulder : B. D, present channel higher than at A, C 



respectively. Scale about 2-1 inches to 1 mile. 



Many of the loose blocks lying on the surface are similar to the 

 rock in situ on either side of the outlet. This suggests that the 

 apparent moraine may in reality be scree, or a mixture of scree and 

 rainwash. On the other hand, many of the boulders in the banks 

 of the stream and in the stream itself are totally different from the 

 rocks on either side, or j» sitil lower down the stream, and we were 

 not able to match them in the immediate neighbourhood. The local 

 rock is a fine-grained, cleaved, and slickensided ash, while most of 

 the boulders proper, which are obviously ice- or water-worn, 

 consist of coarse-grained banded ashes or tuft's, which may possibly 

 liave come from Green Gable. 



