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. i 
The various divisions of the Cretaceous formation in the limited 
area this book describes are, however, marked by real discordances, 
both petrological and palaeontological, 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. XVL j 
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 clifl'-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 
