EUROPE DURING THE GLACIAL PERIOD. 455 



''Evidence has also been found of the invasion of the 

 southern part of this district by ice from the Irish Sea, 

 which is supposed to have traveled up the Bristol Channel 

 from west to east, and to have crossed the Pembrokeshire 

 peninsula from St. David's Head towards Gower and to the 

 neighborhood of Cardiff: erratics believed to have been de- 

 rived from the first-named locality have been found nearly 

 100 miles to the eastward of their probable source. 



"The depth of St. George's Channel between St. David's 

 Head and Ireland, however, exceeds 50 fathoms, and the 

 natural course of the Irish-Sea glacier, joined by those 

 descending the western slopes of the Welsh mountains, 

 should have been southward along the great submarine 

 valley opening out to the Atlantic. The distribution of the 

 erratics just mentioned seems therefore to indicate that the 

 volume of ice, approaching the narrowest part of St. George's 

 Channel, was too great to enable it wholly to escape in that 

 direction, some of it being forced by lateral pressure to travel 

 eastward up the Bristol Channel. 



"It seems worth considering whether so important an ice- 

 stream would not have blocked the entrance to the estuary 

 of the Severn, the result being an accumulation of sedentary 

 ice in the valley of that river, derived partly from the glaciers 

 of central Wales and partly from Atlantic blizzards, which 

 maj r have prevailed at that epoch. 



"This view may possibly throw light on the origin of the 

 great alluvial and lake-like plain of Glastonbury, and of the 

 gorge at Clifton ... It may explain also why Arenig 

 boulders have been piled up on the Clent Hills, southwest 

 of Birmingham, to a height of nearly 900 feet. It is difficult 

 to understand that this could have occurred, if at that time 

 the Welsh ice could have followed an unobstructed course 

 along low ground towards the Bristol Channel. 



"The conditions here sketched out, namely, of ice moving 

 upon central England from the sea in a direction opposed 

 to that of the natural drainage, are precisely those under 

 which glacial lakes with their accompanying over-flow chan- 

 nels would have naturally originated/' 



