193 



there is, as one nsiiully iinds in similar cases, a mass of o-ravel 

 which had been carried throiigli the channel or eroded from it. 

 This has oljstrueted the valley of West Beck, and cansed the 

 formation of Nelly Hay Force. Between the West Beck valley 

 and the valley of the EUer Beck there is an overflow channel 

 across Two Howes Rigg, which is known as Moss Slack. This 

 has an altitude of about 675 feet 



At the time of the greatest extension of the ice, therefore 

 Lake Eskdale, which had a length of at least 1 1 miles, and more 

 probably about 14, and a depth of at least 400 feet, drained at an 

 elevation of 72.5 feet into Lake Wheeldale, which was three miles 

 long, with a surface 675 above present sea-level. Lake Wheeldale 

 overflowed by the Moss Slack channel into a small lake which 

 Mr Kendall has named the YestilnUe or Ellerbeck Lake. 



The HoUins channel did not, however, persist verv lono-. 

 As the ice retreated the overflow from the Eskdale Lake cut 

 successive channels across the moor edge, at lower levels, first by 

 Lady Bridge Slack and Purse Dyke Slack, and then liy Moss 

 Swang and the very striking Randay-Mere A'alley. The Wheeldale 

 and Ellerbeck lakes also became united when the ice retreated 

 from the end of Two Howes Rigg. 



The water which we have thus traced into the Goathland 

 neighbourhood overflowed the Cleveland anticline at Fen Boos at 

 an altitude of about 650 feet The passage of glacial water 

 through this channel persisted for a long M'hile, and the descent 

 into the Pickering valley being steep, the \'ery remarkable 

 valley of Newtondale — the most noteAvorthy of all the British 

 ■overflow channels — was formed. 



The Pickering valley was occupied by a large glacial lake 

 (see Map), and when the turbulent waters discharging down 

 Newtondale reached its quiet shore they deposited their burden of 

 rock fragments, gravel and sand in the form of a large delta 

 extending over at least two or three square miles. The lake 

 itself occupied a very large area, and being dammed in by the 

 ice-front on the east, and the Gilling Gap being also blocked by 

 ice, overflowed into the Plain of York near Kirkham Abbej-, 

 cutting the fine gorge existing at that point, and giving to the 

 river Derwent its erratic inland course. Ultimately, the North 

 Sea being blocked with ice to the northward, the water which had 

 flowed through Lake Eskdale and Lake Pickering found its Avay 

 into the ocean through the Straits of Dover, which it in ail 

 probability assisted to cut, since these Straits did not exist 

 before the Great Ice Age. 



