154 Geological Society: — 



February 6th.— J. J. H. Teall, Esq., M.A., F.R.S., President, 



in the Chair. 

 The following communications were read :— 



1. 'On the Structure and Affinities of the Rhaetic Plant Naiadita? 

 By Miss Igerna B. J. Sollas, B.Sc, Newnham College, Cambridge. 



2. ' On the Origin of the Dunmail Raise (Lake District).' By 

 Richard D. Oldham, Esq., F.G.S. 



The author considers that the gap through the Cumberland hills 

 is a natural feature whose remarkable character has not attracted 

 the attention which it deserves. In form it is an old river-valley, 

 now occupied by much smaller streams than that which formed it. 

 A windgap of this character cannot have been formed by recession 

 of watersheds or capture through erosion, for, in such a case, the 

 stream on one side or the other of the watershed must necessarily 

 fit its valley, while in the Dunmail Raise there is a misfit on both 

 sides. The gap was in existence before the Glacial Period, and 

 consequently cannot have been formed by ice. So, by a process 

 of exclusion, the explanation is arrived at, which fits in with the 

 surface-forms, that the gap of the Dunmail Raise was formed by a 

 river, which flowed across the hills from north to south, and cut down 

 its channel pari passu with the elevation of the hills. The final 

 victory of upheaval over erosion, whereby this river was divided 

 into two separate drainage-systems and the barrier of the Dunmail 

 Raise upheaved, may have synchronized with a diversion of the 

 head-waters and consequent diminution of volume and erosive 

 power. It is pointed out that this explanation comes into conflict 

 with previously published theories of the origin of the drainage- 

 system of the Lake District, inasmuch as the elevation postulated 

 seems too slow to be explicable by the intrusion of a laccolite ; and 

 that the existence of a large river crossing the area of upheaval, and 

 the maintenance of its character as an antecedent river-valley for a 

 long period, show that the surface was originally a peneplain 

 of subaerial denudation, and not a plain of marine sedi- 

 mentation or erosion. From this it follows that the course of the 

 main drainage-valleys may not have been determined by the original 

 uplift, but, with the exception of those which are old river-valleys, 

 whose direction of flow has been reversed on the northern side of 

 the uplift, may have been formed by the cutting-back by erosion 

 into the rising mass of high ground — in other words, that the 

 principal valleys of the Lake District may be subsequent, not 

 consequent in origin. 

 February 20th.— J. J. H. Teall, Esq., M.A., Y.P.R.S., President, 

 in the Chair. 



The following communication was read: — 



' The Geological Succession of the Beds below the Millstone Grit 

 Series of Pen die Hill and their Equivalents in certain other Parts 

 of England.' Bv Wheelton Hind, M.D., B.S., F.R.C.S., F.G.S., and 

 J. Allen Howe, Esq., B.Sc. F.G.S. 



Part I. of this paper consists of a detailed account of the ground. 



