286 EOCENE PERIOD. [Ch. XXI. 



found near Newhaven, and at other points, as will be seen by 

 the map. These are now wasting away, and will in time 

 disappear, as the sea is constantly encroaching and under- 

 mining the subjacent chalk. 



The secondary rocks, depicted on the map, may be divided 

 into five groups : 



1. Chalk and Upper green-sand. This group is the upper- 



most of the series ; it includes the white chalk with and 

 without flints, and an inferior deposit called, provin- 

 cially, ' Firestone,' and by English geologists the < Upper 

 green-sand.' It sometimes consists of loose siliceous 

 sand, containing grains of silicate of iron, but often of 

 firm beds of sandstone and chert. 



2. Blue clay or calcareous marl, called provincially GaulL 



3. Lower green-sand, a very complex group consisting of 



grey, yellowish, and greenish sands, ferruginous sand 

 and sandstone, clay, chert, and siliceous limestone. 



4. Weald clay, composed for the most part of clay without 



intermixture of calcareous matter, but sometimes in- 

 cluding thin beds of sand and shelly limestone. 



5. Hasiinys sands, composed chiefly of sand, sandstone, clay, 



and calcareous grit, passing into limestone *. 



The first three formations above enumerated are of marine 

 origin, the last two, Nos. 4 and 5, contain almost exclusively 

 the remains of fresh-water and amphibious animals. But it is 

 not our intention at present to enlarge upon the organic remains 

 of these formations, as we have merely adverted to the rocks in 

 order that we may describe the changes of position which they 

 have undergone, and the denudation to which they have been 

 exposed since the commencement of the Eocene period, mu- 

 tations which, if our theory be well founded, belong strictly to 

 the history of tertiary phenomena. 



By a glance at the map, the reader may trace at once the 



* For an account of these strata in the south-east of England, sec Mantell's 



Geology of Sussex, and Dr. Fi:ton's Geology of Hastings, where the memoirs of 

 all the writers on this part of England are i\ {'erred to. 



