198 GLACIAL CHANGES IX THE LOWER DEE YALLEY. [June I9I2, 



EiYer Ahven, a tributary of the Dee, about 15 or 20 miles north- 

 west of Llangollen. Borings at the site of the new Birkenhead 

 reservoir proved the old valley below the Boulder Clay and some 

 distance away from the existing river, which has cut well into the 

 solid rock. A similar phenomenon was observed in the excavations 

 for the Rivington Eeservoirs on the old Liverpool ^Yaterworks, 

 where the floor of the pre-Glacial gorge was seen to be about 100 

 feet lower than the present river-bed. 



The Peesidext (Dr. Stkahan) remarked that this paper formed 

 an interesting continuation of the account of the physical history of 

 the Dee given by Ramsay in 1876. With regard to the depression 

 in the rock-surface, proved by borings near Chester, it was to be 

 remembered that it coincided with the outcrop of the Lower Mottled 

 Sandstone, an extremely friable rock which was likely to have 

 suff'ered severely under glaciation. The observations on pre-Glacial 

 valleys made by the Author and Dr. H. Lapworth recalled to mind 

 those of the late Mr. Alellard Eeade on the buried valley of the 

 Mersey near Runcorn. 



The AiJTHOE, in reply, stated that in his opinion there was proof 

 of the correctness of Prof. Charles Lapworth's view that the Severn 

 did not in pre-Glacial times go southwards from Shrewsbury 

 through the Ironbridge Gorge. This would eliminate the possibility 

 suggested by Mr. Lamplugh, that the pre-Glacial Dee may have 

 joined the Severn and gone south. Xo x^roof, however, has yet been 

 found that the two rivers joined and flowed northwards. 



There were no indications in the district of lakes such as had 

 been mentioned by Dr. Wade. 



Dr. H. Lapworth had illustrated a phenomenon that was exceed- 

 ingly common in this area. As another example, the Author 

 instanced the River Alyn near Wrexham, flowing in solid rock the 

 sub-Glacial surface of which slopes away from the present valley. 



The Author considered that it was highly probable that Glacial 

 overdeepening of the Dee Valley had occurred near Chester. He 

 agreed with the President that the soft Triassic rocks of Cheshire 

 would be singularly susceptible to such erosion. 



