Tarns on the Ilaijstacks Mountain, Biittermere. 409 



The outflow valley, though narrow in comparison with the width 

 of the tarn, is broad in proportion to the size of the stream ; it is 

 bounded by steep walls, and below this comes a nearly level 

 surface, which in parts is slightly convex, suggesting the outline of 

 a moraine ; the stream runs at the bottom of a slightly meandering 

 gorge, considerably below the level of this surface. 



Further down the slope of the sides becomes much steeper, and 

 the depth of the gorge increases greatly. At two points, A and 0, 

 are seen portions of former gorge-like channels at a much lower 

 level than the present stream-bed alongside them (see Fig. 3). The 

 lower of these contains an unusually large boulder of banded ash. 

 It seems probable that these deeper gorges are parts of an old 

 pre-Glacial channel, which was filled up by moraine. It is difficult 

 to imagine that sufficient scree material could be derived from the 

 low side-walls of this valley to make any appreciable difference in 

 the level of the stream. The walls of these deeper gorges consist 

 of rock in situ, while in the present channel none is seen until we 

 reach a point far below the level of the lake, where the stream 

 cascades over the crao-s. 



Fig. 4. — Cross-sections of the outlet of Blackbeck Tarn, along the lines X-Y and 

 W-Z of Fig. 3. 



After careful consideration of all the evidence it seems quite clear 

 that this tarn is not a rock-basin, but is held up by some kind of 

 loose material which blocks the outlet, and we incline to the belief 

 that this material is of the nature of moraine rather than scree. 



None of the facts above mentioned throw much light on the past 

 history of the tarn, but it seems very probable that if the old partly 

 buried channel could be cleared out the tarn would be completely 

 drained. Unfortunately we have not, up to the present, been able to 

 obtain any soundings, so that the real depth of the water is unknown : 

 judging from the surrounding slopes, it is not likely to be great. 



Although it is not possible, with the evidence at present at our 

 disposal, to be quite certain, we think it highly probable that this 

 tarn is entirely of post-Glacial date, and it is to be regarded as the 

 direct consequence of the damming of a small pre-Glacial valley by 

 morainic material. 



(2) Haystack Tarn. — The second tarn on the Haystacks is a 

 good deal smaller than Blackbeck Tarn, but still it is of considerable 

 size, covering approximately one and a half acres. It is without 

 a name on the six-inch Ordnance Map, so as a matter of convenience 

 we have named it Haystack Tarn. This tarn is now evidently being 

 rapidly filled up, as shown by the strong growth of rushes and peaty 

 material. It contains several small islands of rock in situ, showing 

 the normal strike of the district, i.e. about E. 30° N. The taru is 



