222 DR. A. jowett on the [June 1914, 



The overflow- channels on the eastern slopes of the Koch Valley 

 are more sporadically distributed, and less easy to arrange in series 

 than those described above. The first stage is marked by a single 

 channel east of the Walsden gorge, which must have been formed 

 Avhen the present gorge was filled with ice up to and somewhat 

 north of the Pennine watershed. A small lake occurred at the 

 head of this channel, but there was doubtless a considerable flow 

 of water towards it between the edge of the ice and the steep slopes 

 of Blackstone Edge. 



The second stage is marked by the overflow from a lake at the 

 head of Longden-End Clough across the ridge to the north. Two 

 sets of small channels (commencing at altitudes of 1225 and 1150 

 feet) conducted the drainage northwards through narrow lakes, the 

 last channel in the series being 125 feet deep on its watershed, 

 which is at an altitude of about 760 feet. This channel terminates 

 close to the entrance to the Walsden gorge. 



The third stage began with a great lake occupying the Tame 

 Valley at an altitude of 1125 feet, which drained northwards 

 into a lake at the head of the Ogden valley (altitude 1100 feet) 

 and thence into the Longden-End lake, from which the water 

 escaped below 850 feet. The last channel in this series is 75 feet 

 deep on its watershed, which was cut down to 675 feet. 



The fourth stage is marked by a series of valleys parallel with 

 those of the third stage, but terminating some 50 feet below, the 

 great channel from the Tame lake being in operation during the 

 earlier part of this stage. The last-mentioned channel cuts down 

 below 625 feet. 



During the fifth stage, a slight overflow of the water impounded 

 against the eastern slopes of the Beal valley entered the lake in 

 the Ogden valley, then at an altitude of 700 feet. The Ogden lake 

 drained northwards into a smaller lake, and then into the Rochdale 

 lake, the last overflow-channel cutting below 600 feet. This stage 

 began with the merging of the Longden-End lake into the Roch- 

 dale lake. 



A slisrht retreat of the ice-barrier led to direct overflow from the 

 Ogden into the Rochdale lake, the channel between the two being 

 cut down below 600 feet before it was finally abandoned and the 

 Ogden lake became part of the Rochdale lake. A lake now 

 existed in the Beal valley, which drained northwards into the Roch- 

 dale lake. This valley continues southwards, but the lowest 

 altitude of its watershed is well over 600 feet, whence we may infer 

 that the waters of the Rochdale lake could not escape in that 

 direction. More probably a northward flow of water took place 

 through this gap into the Beal lake. 



It has been stated that two of the terminal overflow- channels 

 cut down below 600 feet. These are typical dry gorges, and are 

 both directed northwards towards the Walsden gap. The floor of 

 the Walsden gorge is 610 feet on the watershed, and is so level that 



