276 Mr. S . V. Wood on the Events which produced and terminated 



correct, then both basins received the sea-water through the 

 opening at the north-eastern extremity lying in or near the 

 counties of Cambridgeshire, Buckinghamshire, and Bedfordshire ; 

 but if that assumption be untenable, then we have the Anglo- 

 Prankish basin at least land-locked, except at its north-eastern 

 extremity, where alone it communicated with the sea. Now it 

 is apparent from the grouping of the oolitic deposits in the form 

 of concentric rings round the basin, that the closing of the north- 

 western and south-eastern openings was due to that elevatory 

 action which, commencing at the close of the Triassic age, con- 

 tinued with comparatively slight and partial oscillations of level 

 throughout the Jurassic. The last effect of that continuous ele- 

 vation would be the closing of the strait which joined the English 

 basin to the sea, and the conversion of the basin (and with it 

 that of the Charentes) into one receiving fresh water only. 

 Whether the closing of the Charente strait preceded the closing 

 of that in Buckinghamshire and Bedfordshire, or the reverse, 

 will depend on the parallelism that may be established between 

 the Portlandian of the Charentes (upon which the gypsiferous 

 marls of the Purbeck repose) and the Portlandian of Dorset ; 

 but the effect on the basins would in either case be the same in 

 appearance, although in the former case the Purbeck formations 

 of the two depressions would not be exactly synchronous, as the 

 Charente basin would have been converted into one of brackish 

 water before the English depression was severed from the sea, 

 while in the latter the conversion of the English basin into one of 

 brackish water would involve the similar conversion of that of the 

 Charentes, which communicated with the sea through the English 

 basin alone. No traces of the Wealden exist in the Charento- 

 Pyrenean basin, so far as that basin is exposed ; but it is not 

 improbable that towards the more central portions of it, hidden 

 by the overlying cretaceous and tertiary deposits, beds synchro- 

 nous with the Wealden proper of England, and, like it, of purely 

 freshwater origin, may exist. The greater distance of this basin 

 from the principal line of depression (which, as I shall attempt 

 to show, produced the peculiar conditions of the English basin 

 from the Wealden to the commencement of the upper creta- 

 ceous epoch) renders it probable that it underwent a less 

 amount of depression during the Wealden epoch than did the 

 neighbouring basin of England (and this is to a certain extent 

 confirmed by the absence in the Charentes of any lower creta- 

 ceous deposits) ; so that it would be inconsistent to find any purely 

 freshwater deposit extending to the edges of the basin ; and these 

 edges are the only parts of it not covered up by newer deposits. 

 It thus appears to me that in this climax of the elevatory 

 action of the Jurassic age, we have the clue to the configuration 



