1873.] OWEN — DENTIGEROTTS BIRD. 511 



ciple more evident than in considering the structure of the carboni- 

 ferous area of the Mendip Hills, where enormous denudation had 

 taken place long before the New Red Sandstone was deposited. How 

 then could we ignore this operation in other parts of the country ? 

 As to faults, he submitted that their existence must be proved rather 

 than assumed. Did they exist, they were not gaping fractures, but 

 closed ; and he regarded it as physically impossible for such hollows 

 as those in which the lakes were found to be due to such causes. 

 Even if fractures existed, they could only constitute lines of weak- 

 ness, along which denuding agents might more readily work. As to 

 the lakes on the summits of ridges, he would not pretend to account 

 for what he had not seen ; but he cited similar lakes on the Grimsel, 

 which presented similar phenomena, and which he regarded as un- 

 doubtedly due to glacier action. Even on the top of roches mou- 

 tonnees such basins were found ; and though he might not know the 

 exact circumstances under which they were formed, they were un- 

 doubtedly due to ice-action. If in Switzerland and other glaciated 

 countries of the present day we find the configuration of the country 

 presenting similar phenomena to those of Scotland, he considered 

 that there was ample ground for attributing both to the same cause, 

 and there was no need of invoking other causes. It was more- 

 over to be borne in mind that though similar contorted gneissose 

 rocks to those of Scotland occurred in several other countries, it was 

 only in those which had been glaciated that such numerous lake- 

 basins were to be seen. 



The Duke of Argyll, in reply, agreed with Prof. Ramsay that it 

 was not in all cases that the lake-basins were due to disturbance of 

 the rocks ; and indeed in some of the most contorted districts lakes 

 were rarely present. All his contention was that whatever may 

 have been the denuding agent, it was not in all cases ice. 



2. Description of the Settle of a Dentigerotjs Bird (Odontopteryx * 

 toliapictjs, Ow.)from the London Clay of Sheppet. By Professor 

 Owen, F.R.S., F.G.S., &c. 



[Plates XVI. & XVII.] 



Amongst the additions to appear in the second edition of my ' British 

 Fossil Mammals and Birds ' I have anticipated the descriptions of 

 certain species, as in the case of the gigantic Eocene bird, equalling 

 in size the larger New-Zealand Moasf. The still more remarkable 

 Ornitholite, also from Sheppey, which I am now about to describe, 

 has stronger claims to be made known, without delay, on account 

 of the transitional character which it manifests to the Pterosaurian 

 order. 



The fossil consists of a large portion of the skull, which, when 

 the specimen was received in the British Museum, was more or less 

 imbedded in the London Clay • the clearing out of the matrix by the 



* Gr. odovs, tooth ; irrepv^, wing of bird, 

 t Dasornis londinensis, Trans. Zool. Soc. vol. vii. p. 145, pi. 16. 



2m2 



