150 



Stainmoor. In other words, I regard them as of the same age, 

 and as primarily due to the same set of causes. The contortions 

 on the top of the section at Erith (fig. 7) — that is to say the 

 "Trail" — date from the period when the icy barrier was retiring, 

 in other words, to the period when our Cumberland and Westmor- 

 land drifts were in course of formation. 



Horizontal passage of Till into Sand and Gravel. — There is very 

 little to add to what I have stated above in regard to the horizontal 

 passage of Till into deposits consisting chiefly of water-worn and 

 rounded materials. These last are, I think, simply the ordinary 

 materials liberated from the ice as it melted, but modified more or 

 less by the rolling and wearing consequent upon the action of the 

 water proceeding from the melting of the ice nearer the margin of 

 each basin. One would expect, from the very nature of the causes 

 at work, that where the sediment liberated from the ice lay in the 

 path of larger bodies of water in movement, the materials of that 

 sediment would be more or less modified in consequence. And 

 that is exactly what is the case as a rule. 



Undisturbed deposits beneath Boulder Clays. — The existence of 

 soft and incoherent strata lying apparently without any signs of dis- 

 turbance underneath boulder clay, and in places that have almost 

 certainly been traversed by thick masses of ice in motion, has often 

 given rise to much discussion, and has been explained in a variety 

 of ways. In many such cases in East Anglia, for example, there seems 

 to be no doubt, as Mr. Reid has pointed out, that some of the older 

 deposits were, during the periods of more intense glaciation, com- 

 pacted by freezing into masses as hard as the ice itself. I am in- 

 clined to think that there were also other factors at work, which will 

 have to be taken into account. Amongst these I think we must not 

 overlook the angle of thrust of the moving ice. Where the direction 

 of thrust formed a large angle with the surface affected, there cannot 

 be much doubt that considerable disturbance would result, and any 

 quantity of the rock affected might, in time, be removed. But 

 where the direction of thrust formed a very low angle with the 

 surface, as it usually did far away from the influence of the higher 



