288 



THE GEOLOGIST. 



every age varies with their geographical extension, and according to 

 the ancient conditions of that part of the Cretaceous sea on which 

 they were deposited. Thus in places far removed from Kent the 

 argillaceous gault of England may be represented by a hard rock or 

 an incoherent sand ; or the fossils of the Upper Cretaceous beds may 

 be enclosed in strata totally unlike the soft white chalk of England; 

 the upper beds of which, too, in some parts of Europe are devoid of 

 those bands of black flints which so conspicuously characterize our 

 own : while on the other hand the Lower Chalk which is here with- 

 out them, elsewhere on the Continent encloses numerous bands of 

 siliceous concretions. The grey chalk also in some places abroad 

 contains white-coated flints and beds of chert, and may be represented 

 by a limestone in one geographical district, and by a sand or a clay 

 in another. 



The various divisions of the Cretaceous formation in the limited 

 area this book describes are, however, marked by real discordances, 

 both petrological and palseontological, while some connecting organic 

 forms link the whole into one proper geological group, containing 

 upwards of 5000 characteristic species of fossils distinct from those 

 of the Oolitic strata below, and from those of the Tertiary beds 

 above. 



But to return to our history, from which we have thus somewhat 

 digressed. All these strata, which we have so far traced as sea-de- 

 posits, have been raised from their nearly level position and tilted 

 with slightly upturned edges. In our section (fig. 1) they dip 7° 

 to the east-north-east. In Sussex the like beds dip the opposite way, 

 and they vary all round the semicircle of the Downs, assuming a 

 more and more northerly dip as they approach from either hand its 

 central portion in Surrey ; pointing indeed away in all directions from 

 a common centre near Battel, in Sussex, as may be seen in the map, 

 PI. XVI. 



At intervals these chalk downs are broken by transverse gorges or 

 river- valleys, while the great interior area of the "Weald presents the 

 lowermost, or, as from this circumstance they are termed, the Wealden 

 strata at the surface entirely divested of those cretaceous sand- 

 stones, clays, and chalks, which in the Kentish cliff-section are seen 

 to repose upon them. 



Now either those chalk-strata and greensand were never deposited 

 over this area, which their thickness at their truncated edges, as well 

 as the steepness and height of the surrounding escarpment of the 



