76 



absence of wave motion in the sea, owing to the presence of icefloes 

 on its surface, or to the rapidity of the emergence. 



Origin of the Upper Boulder Clay. The Upper Boulder Clay 

 was probably formed in the same manner as the Lower Boulder 

 Clay, but during a second submergence of the land. The receding 

 glaciers would then move over the Middle Sands and Gravels, 

 which would no doubt, in some cases, be contorted, in others 

 removed altogether. At the same time the Lower Boulder Clay 

 might be denuded in places, especially on valley sides facing the 

 moving glacier. The sands, gravels, and boulder clay over which 

 the glaciers moved this time being everywhere nearly uniform in 

 mineralogical character, the resulting clay would no doubt be ot 

 the same colour throughout, and be more sandy than the lower 

 clay, owing to the presence of sandstone boulders in the beds 

 over which the glaciers passed. These inferences are in strict 

 correspondence with the results of observation. 



An explanation which requires two submergences to produce 

 the tripartite form of the deposits is no doubt complicated ; but 

 nevertheless, it seems right, for I have elsewhere shewn from positive 

 observation, that in the neighbouring district of Furness there 

 occurred an inter-glacial period of sufficient duration for the 

 accumulation of immense quantities of vegetable matter character- 

 istic of a temperate climate ; so that two invasions of the glaciers 

 seem necessary, and consequently two recessions of the same. 



Origin of Mounds of Sands and Gravels. The mounds of sand 

 and gravel occurring at the mouth of valleys probably originated 

 at a time when the glaciers were shrinking back into the hills, and 

 the Upper Boulder Clay was being formed. Sea-currents having 

 the directions indicated by the boulder dispersal, would move 

 right across the mouth of most of the valleys, which would at that 

 time be fiords. The water in those fiords would be almost motion- 

 less, except near the mouth, where there would be an eddy, produced 

 by the current outside striking against the farther point of the fiord, 

 and being thereby deflected inward, as shewn in Fig. 14. Bergs passing 

 along the coast outside the fiord would no doubt often find their 



