185/.] KIRKBY PERMIAN FOSSILS. 213 



former existence of horizontal strata of — 1. (lowermost) loam with 

 flints, — 2. greenish sands with ironstone nodules, — 3. yellow and 

 reddish sands, — superposed on the bare chalk, after the eocene beds 

 were for the most part denuded, and before the sandpipes were 

 formed, into which these overlying beds were here and there let 

 down and thereby preserved when further denuding agencies removed 

 the later tertiary beds. 



Regarding then the outliers of ferruginous sands and sandstones 

 above referred to as of the age of the Lower Crag, Mr. Prestwich 

 pointed out the relative position of beds of similar structure on the 

 Downs between Calais and Boulogne, and on the top of Cassel Hill 

 near Dunkirk ; and of others at Louvain, and at Diest in Belgium, 

 mentioned by M. Dumout and Sir C. Lyell. This extensive range of 

 Crag-beds to the south of the typical Suffolk area, and their con- 

 siderable elevation above the sea, are of course matters of great in- 

 terest, not only as pointing out the relative age of some of the drifts, 

 but especially as giving us a still nearer date to limit the denudation 

 of the Weald, and indicating marginal sea-beds now stretching far 

 inland and ranging once probably over the Wealden area, — possibly 

 connected too with the Carentan beds of Normandy. 



With regard to the denudation of the Weald, Mr. Prestwich sug- 

 gests that, the anticlinal axis of the Weald having been somewhat 

 raised during the cretaceous period, and the lower tertiaries partly 

 constructed from its debris and gradually distributed over its area, it 

 was again denuded to a further extent in the later tertiary period, 

 some island or islands of the lower cretaceous rocks remaining in its 

 area from which for the most part these sandy ferruginous Crag-beds 

 were derived. The great or final elevation and denudation of the 

 Wealden area was necessarily subsequent to the deposition of these 

 pliocene beds, for their outliers, resting on an old flint-drift, occur on 

 the very edge of the upraised chalk-escarpments of the Weald. This 

 elevation being also subsequent in time to the first or Lower Crag 

 period, Mr. Prestwich suggests, that we have here evidence of the 

 physical cause of the distinction of the two Crag periods. The first 

 Crag sea was open to the south, and of considerable extent ; but the 

 last Wealden elevation, cutting off" the southern portion, so altered 

 the hydrographical conditions of the period, that a sea open only to 

 the north remained, in which the Red or Upper Crag, with its par- 

 tially boreal fauna, was then deposited. 



2. On some Permian Fossils /^om Durham. 

 By J. W. KiRKBY, Esq. 



[Communicated by T. Davidson, Esq., F.G.S.] 



[Plate VII.] 



This communication comprises a notice of the occurrence of a 

 malacostracous Crustacean and of a new species of Chiton in the 



a2 



