A>fD OF THE J^EIGHBOUEHOOD OF AVATFOED. 91 



Tertiary series was laid down upon it, but the latter extended over 

 a large jwrtion of the Chalk, and was subsequently let down by 

 the same distiu'bance which affected the Chalk formation. I mention 

 this that you may get a clear idea of the term "basin"; because, if 

 it were simply a basin scooped out of the Chalk, in which the strata 

 were successively deposited, we should naturally imagine that the 

 oldest groups, as this basin was filled up, would have gradually 

 succeeded each other in a more or less horizontal order, so that 

 the newest, or last formed, would occur in the centre as well as 

 on the margins of the basin. This is not the case. When we 

 examine a geological diagram, as the one above alluded to, we find, 

 in proceeding from the margins on each side towards the centre, a 

 series of beds of similar kinds successively cropping out or exposed 

 on each side, except where concealed by superficial gravels, thus 

 showing that they are continuous beneath, and are limited within 

 the basin. Hence you see that the trough-shaped arrangement 

 was formed, not by the deposition of successive strata in a basin of 

 the Chalk previously cut out, but that the newer beds were depo- 

 sited over a broad and level surface, and have partaken of the 

 movements to which the Chalk has been subjected. 



This we know from the study of the general geology of southern 

 England. If we made a traverse from this district or the Hert- 

 fordshire Chalk hills over the London Basin to the North Downs, 

 and again across the Yalley of the Weald to the South Downs, we 

 should find the Wealden area a raised dome, occupying part of a 

 great vault or anticlinal fold, the London Basin lying in what is 

 called a synclinal trough to the north. If we continued the section 

 across the Channel into the French area, it would be seen that 

 the Chalk re-appears both north and south of Paris, forming 

 another trough, in which are inclosed Eocene strata similar to those 

 of the Isle of Wight, and thus forming the so-called Paris Basin. 

 Hence the Paris and London Basins with their Eocene strata 

 occupy two synclinal folds, the result of one or more movements 

 by which the anticlinal axis of the Wealden area, and similar 

 parallel ones in the south of England and part of France, have 

 been produced.* In fact, the general teaching is, that after the 



* M. Ch. Barrois has published some interesting papers (' Ann. Soc. Geol. du 

 Nord,' tomeii. p. 85; 'Ee\iie Scientifique,' 1875, pp. 1070, 1192J on the undula- 

 tions of the Chalk in the south of England, and their probable continuation with 

 similar folds and faults in the north of France. M. Barrois recognises three 

 great anticlinal lines or axes of elevation : — 1. The axis of Kingsclere, in an 

 east and west direction, has separated the basin of London from that of Hamp- 

 shire, and the movement which determined it took place between the Chalk with 

 Marsupites and that with Belemnitella, and more slowly towards the end of the 

 Eocene period. The axis of Artois is considered to be" a continuation of that of 

 Kingsclere. 2. The axis of "Winchester. This axis is parallel to the preceding, 

 was formed dm-iug the same period, and is thought to be a prolongation of the 

 axis of the Bresle. It is probable, however, that this axis, as well as that of 

 Artois, underwent the last movement during the Upper Eocene. 3. The axis of 

 the Isle of Wight and Pm-beck. This axis is parallel to the two preceding, and 

 its elevation and that of Kingsclere has given the basin-shaped arrangement to 

 the Chalk of Hampshire. Its last movement was about the period of the Barton 



