THE BEDSHIEL KATMS 311 



It enables U8 also to account for the correspondence between 

 the internal structure of these mounds and their external 

 form, and for the fact that sheets of fine material, such as 

 bauds of clay, form some of the highly-inclined layers which 

 wrap around the beds of sand and gravel. 



It enables us, further, to account for the presence, in the 

 Eskers, of stones which have travelled thither from every point 

 of the compass, as well as for the occurrence in them of stones 

 that lie at levels higher than that of their parent sources. 



Finally, the same ex[)lanation gives us a really satisfactory 

 account of the reason wh}' these mounds so often assume 

 steep-sided forms, why they end off so abruptly, and why 

 they so often enclose land-locked hollows or " kettle holes." 

 It may be as well to mention that this explanation of the 

 origin of Eskers was read by the present writer before the 

 Geological Society of London, on the 24th of June 1874 ; 

 and that it was first published in the Geological Magazine 

 for November of that year. 



Concerning the sequence of events that followed the 

 building of the Eskers not much may be said. When the 

 ice finally disappeared the land stood at a lower level by 

 about a hundred and fifty feet than it does at present. 

 There is no valid evidence of any greater submergence at 

 any time daring the Glacial Period in Britain. The occur- 

 rence of the shelly beds on Moel Tryfaen, in North Wales, 

 can be easily explained on the supposition that part of the 

 ice in the Irish Sea incorporated some of the old sea-bottom, 

 shells and all, and that these worked their way up to the 

 higher parts of the ice in the way already described, and 

 were subsequently melted out where they are now. This 

 was my original statement in the Geological Magazine for 

 November 1874, and I never expressed tlie belief that these 

 shells had been pushed up by the ice, as most subsequent 

 writers have stated. The shelly beds at Airdrie never had 

 any existence ; the whole statement that they did occur 

 there was purely a fiction. 



The shelly boulder clay described by Mr Gunn, of the 

 Geological Survey, as occurring in the banks of the Tweed 

 just west of Berwick, was probably formed during the 

 period of submergence. I have gathered from it several 



