288 On the Purbeck and Wealden Deposits of England and France. 



conditions not dissimilar to those of the latter basin, that is, that 

 during the Jurassic age it was a basin becoming more and more 

 landlocked with each successive epoch, under the elevatory 

 influence of the system of Portugal and England, on the eastern 

 flank of which, like the Anglo-Frankish basin, it existed, until 

 at the close of the Jurassic age it ceased for a long interval to be 

 a marine basin, all connexion between it and the ocean being 

 severed by the elevation, at the close of the Purbeck epoch, of 

 the strait communicating with the basin of England and Prance. 

 After the lapse of this long interval, when the sea during the 

 upper cretaceous age occupied both basins, there appears no 

 reason for assuming that any connexion between them again 

 existed. It is true that, according to the researches of MM. 

 Triger, Saemann, and Coquand, features occur in the grouping 

 of the upper cretaceous deposits of La Sarthe (forming the 

 south-western margin of the Anglo-Frankish basin) similar in 

 all respects to those occurring in the Charentes, and indicating 

 a corresponding amount of depression during the upper cre- 

 taceous epoch on either side of the isthmus formed by the 

 Jurassic deposits of the Vienne ; but this similarity has refer- 

 ence to a correspondence of depression only, and not to an 

 intimate zoological connexion — the zoological relations of the 

 upper cretaceous deposits of the Charentes appearing to be with 

 those of the Pyrenees rather than with those of England and North 

 France *. It appears to me, therefore, that while, during the 

 upper cretaceous age, the Anglo-Frankish basin was well opened 

 to the ocean north-eastwards by the subsidence of the palaeozoic 

 barrier, the Charento-Pyrenean basin was opened in the con- 

 trary direction to the ocean by the subsidence of the tract which, 

 during the previous part of the mesozoic period, joined Portugal 

 to England, and bounded that basin on the west, but that both 

 series of movements were alike correlated to or consequent upon 

 the elevation of the Pyrenean chain then in progress. In using 

 the expression " correlated to or consequent upon," I desire to 

 guard myself against being understood to mean that these move- 

 ments were entirely synchronous with the elevation of the Pyre- 

 nees. Indeed it is not improbable that the subsidence of the 

 palaeozoic barrier preceded the elevation of the Pyrenees ; but the 

 relation of the movements in either area to each other was due 

 to one great band of volcanic action, which came into existence 

 from west to east during the lower cretaceous age, and of which 

 we have the most conspicuous effects exhibited in the great anti- 

 clinal of the Pyrenees, and consequently refer to it, in one com- 

 prehensive term, as the system of that chain. 



♦ Lyell's 'Manual/ 1851, p. 221. 



