566 Notices of Memoirs — Prof. Soilas — Glaciers. 



in a complete rock bar. Beside the present course of the effluent 

 stream is a parallel strip of moraine running down towards Llyn 

 Llydaw, but living rock soon appears in this in such a way as to 

 Bhow that if there be any old channel in this direction it must be 

 exceedingly narrow and tortuous. If this lake be not contained in- 

 a true rock-basin it must be very shallow, or else must have found 

 exit by a gorge quite as narrow as those found at the end of some 

 of the Swiss glaciers. 



Immense quantities of moraine material occur on the south-east 

 side of Llyn Llydaw, but a careful examination of the map and the 

 ground shows that only two possible outlets exist, that now used 

 tor this purpose, and a second which is occupied by bog resting on 

 moraine, and gives rise to a small stream which is joined lower 

 down by the outlet of Llyn Teyrn. The moraine is, however, only 

 a thin skin on the surface of rock. The present outlet shows live 

 rock 40 or 60 feet below the level of the lake, and the second 

 possible exit at a rather less distance below the same level. If the 

 moraine were stripped off, there is little doubt that this lake, like 

 Glaslyn, w^ould show a basin of rock which would hold water, 

 unless it is very much shallower than is generally supposed to be 

 the case. 



II. — On Pitch Glaciers or Poissiers. By Prof. W. J. Sollas, 



D.Sc, F.R.S. 1 



PITCH and the ice of glaciers strikingly resemble each other in 

 behaving as solids or liquids, according to their manner of 

 treatment. On the sudden application of torce they break like 

 brittle material, but behave as fluids when subjected to gradual pull 

 or pressure. Hence it is possible to employ pitch in the construction 

 of working models of glaciers in oi'der to obtain an insight into 

 those internal movements of actual glaciers which are beyond the 

 reach of direct observation. The study of glacial deposits has 

 shown that many erratic boulders were transported, during the 

 Glacial period, from lower to higher levels, and left stranded on 

 the flanks of mountains some hundreds of feet above their source. 



This standing difficulty in the way of physical theories of glacier- 

 movement has been explained by the study of pitch models, which 

 show that the lower layers of material on approaching an obstacle 

 are carried up in an ascending current. The inference, which is 

 confirmed by other kinds of observation, is that similar movements 

 tnke place in actual glaciers. Further, a glacier sometimes over- 

 rides its terminal moraine without disturbing it ; and in an experi- 

 ment this was exemplified, for pitch flowed for several months over 

 a ridge of loose material without carrying a particle of it away. 

 A i-emark made by Professor Fitzgerald to the effect that viscosity 

 seemed merely to retard, not to alter the nature of, the movement, 

 in the cases described, led the author to experiment with less viscous 

 material, such as Canada balsam and glycerine, with concordant 



^ fiead before Section C of the British Association at Ipswich, September, 1895. 



