220 dr. a. jowett ox the [June 1914,. 



(b) The Walsden Series. 



At a very early stage, when an ice-lobe occupied the Walsden 

 valle}% a small lake existed in the Upper Irwell Valley, and pro- 

 bably drained directly into the Calder basin through the gap at 

 Sharney Ford near Bacup. It overflowed later across the ridge 

 into a small lake at the head of the Wardle valley, which may have 

 first discharged across the watershed on the north-east. 



As soon as the entrance of the Walsden gorge was exposed by 

 the south-westward retreat of the ice in the valley of the Roch r 

 other glacier-lakes began to form at the heads of the valleys 

 on the south of the Rossendale highland and on the west of the 

 Pennines. The channels cut by the overflow from these lakes 

 are directed eastwards and northwards respectively towards the- 

 Walsden gorge. 



There are four well-defined stages of retreat of the ice-barrier 

 from the hills north of the Poch Valley — during which the drainage 

 was directed eastwards, and crossed the Pennines by way of the 

 Walsden gorge. 



The retreat of the ice south of Shore Moor provided a new out- 

 let for the Wardle lake, and a series of channels was cut, which 

 drained eastwards before the entrance to the Walsden gorge was 

 entirely ice-free. 



During the next stage, a series of large channels was formed, 

 the last of which cut down nearly to 800 feet close to the entrance 

 to the Walsden channel. A small lake in Naden Dean overflowed 

 into a large lake that extended across the watershed in the Whit- 

 worth and Upper Irwell valleys, the surplus water from which 

 passed into the Wardle lake and so into the Walsden channel. 



The third stage is rather more complicated. When the ice- 

 barrier retreated sufficiently to expose the wide gap south-west of 

 Brown Wardle Hill, the Whitworth lake would fall rapidly to^ 

 below 1000 feet, the overflow taking place eastwards into the 

 Wardle lake. This necessarily led to the separation between the 

 Upper Irwell lake and the Whitworth lake, as the watershed 

 between them stood at an altitude of 1050 feet. Water from 

 the Irwell lake continued to escape southwards across the water- 

 shed into the Whitworth lake, cutting a channel, now dry, below 

 1000 feet ; and the Whitworth lake overflowed into the Wardle lake 

 through the above-mentioned gap, until its waters sank below 

 950 feet. 



The Irwell lake must by this time have become much larger. 

 That the ice-barrier north of the Rossendale highland was higher 

 at this stage than that on the south is proved by the fact that 

 two dry overflow-channels occur at the head of the Limy- Water 

 valley, which cut below 1000 feet and down to 1050 feet respec- 

 tively, and are both directed southwards. With a higher ice- 

 barrier on the south, they must have been directed northwards. 

 They were produced at a later stage by an overflow from small 



