298 



THE WONDERS OF GEOLOGY. Lect. IV. 



natural order of succession. A similar section is seen 

 in Compton Bay ; while along the Undercliff, fallen masses 

 of the upper beds, intermingled with detritus, form the 

 ruinous cliffs of that picturesque tract ; and beyond, at 

 Black-gang and Atherfield, the greensand series constitutes 

 the line of coast ; the Wealden forming the cliffs in Brixton 

 and Brook bays ; but the details of this interesting district 

 are so fully given in my recent work,* that I need not 

 enter at length upon the subject. 



4. Chalk Downs. — The features of a chalk district are 

 very peculiar, when the surface has not been broken up for 

 tillage, or is not concealed by dense woods and forests. The 

 rounded summits of the hills clothed with short verdant 

 turf — the smooth undulated outlines of the Downs, unbroken 

 save by the sepulchral mounds of the early inhabitants of 

 the country — the coombes and furrows, ramifying and ex- 

 tending into the deep valleys which abruptly terminate at 

 the base of the hills, and appear like dried up channels of 

 rivulets and streams, though free from all traces of alluvial 

 debris ; thus bearing the impress of physical operations of 

 which the agents that produced them have long since passed 

 away — are phenomena that must be familiar to every one 

 who has travelled over the downs of the south-east of Eng- 

 land. These features are restricted to the hilly districts where 

 the white-chalk forms the subsoil, and have resulted from 

 the peculiar nature of the sedimentary detritus of which 

 the strata comprised in the upper division of the cretaceous 

 system are composed. For where the lower group of clays, 

 marls, sands, and sandstones approaches the surface and 

 forms the subsoil, the country is broken and diversified, and 

 the landscape presents a striking contrast with the down 

 scenery. 



* Geological Excursions round the Isle of Wight and along the 

 adjacent Coast of Dorsetshire, 1 vol. 8vo. with numerous illustrations, 

 .sections, map, &c. 11. 0. Bohn, London, 1847. 



