6 G. F. Wright— Theory of an 



the gulley by ice in its passage southward across the harbor," 

 for they were so scattered through the unstratified mass that it 

 Mas impossible to draw a line between the shelly and the shell- 

 less clay.* In the glacial deposits surmounting the chalk cliffs 

 near Flamborough Head, Mr. Lam pi ugh showed me elongated 

 masses of sandy material containing well-preserved shells, but 

 which were included in till, and had evidently been drawn out 

 by the shearing movement to which the whole mass was sub- 

 jected. There could be little question that in this instance the 

 mass had in some way been pushed up from the sea bottom by 

 the same ice-movement which had carried thither the rest of 

 the till. Here the elevation was between 200 and 300 feet, 

 and I see no reason why the causes operating to produce that 

 amount of movement and elevation might not under favorable 

 conditions have transported similar masses to the elevation of 

 the shell-beds at Moel-Tryfaen. 



In recent speculations upon the movement of ice too exclu- 

 sive attention has been given to its analogies with the motion 

 of a semi fluid, forgetting that under a mechanical thrust ice 

 moves like a solid, and may plough up and push along before 

 it whatever is in its way. Indeed, as I recall the phenomena 

 at Muir glacier, I feel confident that this is what is taking 

 place on the bottom of the inlet. A large number of the ice- 

 bergs are formed by the falling off of the precipitous ice-front, 

 owing doubtless to the fact that in the ordinary motion of the 

 glacier the upper strata move faster than the lower. At times 

 I saw such masses break off in columns more than 250 feet in 

 height, and extending below the surface of the water, but the 

 fractures did not reach to the bottom of the ice, for occa- 

 sionally an immense mass in front of the ice-wall would rise 

 bodily out of the depths of the water, bringing up much dirt 

 with it. This projecting foot of the ice may perhaps have 

 been moved forward bodily at the bottom of the inlet by 

 successive mechanical thrusts of the moving mass of ice behind. 

 So in analogous situations where there is a concentration of 

 lines of pressure from behind, we can conceive that material 

 would be gradually thrust up in front of the ice without much 

 attrition. At any rate, the fact that the material is so raised 

 and pushed along in front of the ice I think will have to be 

 accepted. 



Returning now to the specific glacial phenomena in Eng- 

 land, it would seem that they can be generalized under one 

 glacial epoch, upon the following scheme, which is based upon 

 the facts as they are now reported. The beginning of the 

 glacial period was marked, in the seas surrounding England,. 



* Quarterly Journal of the Geological Society, Aug. 1886, p. 283. 



