128 T. M. EE1DE ON THE DKIFT-BEDS OP THE 



mountain scenery, as relates to our present subject, is, as compared 

 with, the plains, the absence of Drift. This, perhaps, seems what we 

 might naturally expect from the Postglacial denudation which it 

 has since undergone. But in the region of lakes we find lakes 

 still ; and one would expect that if much material had ever existed 

 in the drainage-basins in the form of Drift, it would in travelling 

 down streams be caught in the lakes ; and hence we might expect 

 them to be now filled up. There are no means of estimating the 

 actual amount of material that has thus been entrapped ; a series of 

 borings would be required to do this. But I would point out that 

 the whole of the material brought down is not deposited in the 

 lake ; on the contrary, we find the shores of lakes pretty generally 

 formed of shingle and gravel. The wind-waves must move this ; 

 and doubtless in most cases there is a general progression of materials 

 along the shore, and eventually down stream from the outlet. This 

 may account for some of the material ; and the generally limited 

 area of the drainage-basins in mountain-districts will also tend to 

 explain the absence of great quantities of Drift. It will be seen, 

 and it is in accordance with the theory here put forth, that the 

 larger the drainage-basin in which the Drift lies the greater is its 

 quantity. In this way it is that the plains of Lancashire are so 

 drift- covered, while the hilly tracts are to a large extent driftless. 

 The Drift met with in the mountain-valleys I have described is 

 usually either true Till or boulder- and gravel-drift, when found 

 together, the latter usually overlying the former. The Till most 

 probably has been formed under or in front of the local glaciers 

 during their recession. 



That the ice lingered longer about the mountains than elsewhere 

 is proved hy the iceberg-borne erratics of the Lancashire Boulder- 

 clay. Consequently, while the Drift of the plains was being formed, 

 the greater part, if not the whole, of the materials denuded from the 

 mountains and valleys was pushed forwards by the glaciers and 

 protruded into the sea. I have shown how at the Atlantic Docks 

 the majority of the large erratic stones, deeply grooved and worn, 

 are in the upper bed of plastic clay. The boulders in the lower 

 beds are more frequently rounded. This fact corresponds with what 

 would happen under the sequence of events the theory assumes. The 

 larger stones would not be conveyed away until there was depth of 

 water sufficient for the flotation of the iceberg. 



But I have shown that an enormous amount of material has 

 come down from the Welsh mountains in the form of boulders and 

 shingle, which is distributed on the plains into which these valleys 

 debouch ; and it is extremely probable that much of it has been 

 moved to its present position during and since the emergence of the 

 land from the sea. 



Conclusion 



I fear that my views will not appeal to the imagination in so 

 lively a fashion as do some at present in vogue ; but of this I am 

 sure, I have been animated by the sole desire of seeing things as 



