the Purbeck and Wealden Deposits of England and France, 285 



Dr. Fitton as of Purbeck or Wealden age, undoubtedly belong 

 to the Anglo-Frankish basin ; but whether they are to be referred 

 to the Purbeck or to the Wealden, or to neither, but to the over- 

 lying or underlying marine formations, is a matter of much 

 doubt ; at least we may affirm that, if they are eventually re- 

 ferred either to the Purbeck or Wealden, they formed the ex- 

 treme south-easternmost margin of the lake. The other nu- 

 viatile formations of oolitic age, viz. those of the Hautes Alpes, of 

 Skye, of Sutherlandshire, and of Lincolnshire, have no geogra- 

 phical relation to the formations occurring in the South-east of 

 England, or, except those of Skye and Sutherlandshire, with 

 each other. The great Purbeck- Wealden formation of Hanover, 

 although most probably synchronous with the similar formations 

 of the South-east of England, was manifestly geographically se- 

 vered from them by the palaeozoic barrier. On the other hand, 

 the fluviatile deposits of Beauvais, and those described by M. 

 Coquand as occurring in the Isle of Aix, belong to a later geolo- 

 gical horizon, and have no connexion either geographically or 

 geologically with the fluviatile formations discussed in this paper. 



It follows also, from the conclusions here drawn, that the 

 marine equivalent of the Wealden (the lower Neocomian of the 

 South-east of France) should occur in the north-eastern counties 

 of England beyond the north-east opening, being necessarily 

 absent over that area which the Anglo-Frankish basin occupied 

 during the progress of the Wealden deposit. In these counties 

 and in Western Norfolk, however, the contiguity of the shore may 

 have rendered the water too shoal to permit of the deposit of 

 any older cretaceous formations approaching in thickness to the 

 lower greensand of the basin itself, and in West Norfolk the 

 action of the tide setting in towards the opening may have 

 tended to check the accumulation of sediment. 



In considering the sources and direction from which came 

 the waters that fed the basin with sediment during the Wealden 

 epoch, we have to consider the nature of this sediment, and the 

 character during the time of its deposit of the land which sur- 

 rounded the basin. As to the first, those who have made the 

 Wealden their study appear agreed that the source of the sedi- 

 ment was chiefly an area of metamorphic rocks. The absence 

 or rarity of limestone in the beds of the Wealden itself is one 

 of its most marked features ; but this absence may not be alto- 

 gether due to the drainage-area being destitute of limestone 

 tracts ; the soluble nature of lime permits of its being carried 

 into the sea, and held there in suspension after all the alumi- 

 nous and siliceous sediment has been deposited. The rarity of 

 limestone cannot, therefore, I think be adduced as an argument 

 that the Wealden waters were derived from an area in which the 



