Yol. 57'] ORIGIN OF THE DTJNMAIL EAISE. 195 



that which concerns the origin of the drainage-S3'stem. This is 

 generally regarded as having been marked out, in its main features, 

 at the time of the original uplift on the surface of the Carbo- 

 niferous, and possibly newer, rocks which are believed to have 

 extended across the region now occupied by the mountains of the 

 Lake District. In other words, the principal valleys are regarded 

 as originally consequent on this uplift, their direction being 

 determined by the slope given to the original plain, whether of 

 deposition or marine denudation, and as being superimposed 

 on the rocks out of which they are now carved. This last hypothesis 

 is unaffected by the explanation of the Dunmail Raise here offered, 

 but the first is seriously affected. If my explanation is correct, it 

 follows that a well-established river crossed the uplift at the time 

 of its commencement, and this river was sufficiently powerful to cut 

 down its channel as the uplift proceeded, continuing for a long 

 time as an antecedent river. This practically necessitates the 

 conclusion that the surface, affected and modified by this elevation, 

 was not a plain of marine deposition or denudation, but a 

 peneplain of subaerial denudation,^ and it is possible that the 

 principal northern drainage-lines other than the Thirlmere Valley 

 were determined by reversals of the original drainage of the pene- 

 plain, due to the changes of level and slope caused by the elevation, 

 in which case the valleys are reversed; but it is more probable 

 that the present drainage-system was largely determined by a modifi- 

 cation of the old one through cutting back by erosion into the rising 

 mass of high ground,^ in which case the principal lines of drainage 

 must be regarded as subsequent. 



This is, however, subsidiary to the main object of this communi- 

 cation, the explanation of the Dunmail Eaise. The questions of 

 what was the original extent of the drainage-area of the Dunmail 

 River, and of what was the origin of the other drainage-lines in the 

 Lake District, demand a more detailed and extended study than I 

 have been, or am likely to be, able to devote to them. They will 

 in any case be difficult to answer, and in view of the great changes 

 in the details of surface-forms wrought during the Ice Age, it 

 may be doubted whether they will ever be capable of certain 

 solution. 



Discussion. 



Dr. H. R. Mill said that he believed the radiate symmetry of the 

 valleys of the Lake District was first referred to by the poet 

 Wordsworth, who considered only the western half of the district 

 with Sea Eell as a centre. He himself had used the idea of radiate 

 symmetry as a convenient way of fixing the somewhat difficult con- 

 figuration of the district in the mind of a reader unacquainted 

 with the region ; and while naturally interested and pleased when 



^ This conclusion will of course be strengthened, if the suggestion regarding 

 the origin of the Kirkstone Pass (footnote S p. 193) is accepted. 



- With the possible exceptions of the Borrowdale and Ullswater valleys, 

 see footnote, p. 194. 



