HANDBOOK Of FOSSILS. 83 



Cambridgeshire; lately it has been found as far west as 

 Exeter. 



2. Neocomian. 



a. The so-called Lower Green Sand, named in contradistinction 

 to the Upper Green Sand, includes a 



series of iron stained sands, sandstones 

 and clays of great thickness. The 

 clayey beds are seen at Atherfield in 

 the Isle of Wight, and at Nutfield in 

 Surrey, while the sandy beds are met 

 with at Speeton, at Folkestone, and 

 near Reigate. Besides brachiopods 

 and oysters, these beds have furnished 

 a species of Perna (P. Mulleti], an 

 elongated mussel {Gervillia anceps), 

 a pretty Trigonia (71 cordata), some 

 Ammonites and Nautili, with the teeth 

 and bones of big reptiles. The cele- 

 brated " Kentish Rag " and the sponge 

 gravels of Farringdon are of this age. 



b. Wealden. The main mass of 

 these rocks occupies the area inclosed 



between the North and South Downs, Inoceramus concentrictts 

 and forms the Valley of the Weald, (from the Gault). 



whence they take their name. They consist of a series of sands, 

 sandstones, clays, and shelly limestones that were deposited in 

 the delta and off the mouth of a big river. The shells in them 

 belong to freshwater genera, Cyrena, Unio, Paludina, etc. Bones 

 of a huge lizard that hopped along on his hind legs (Iguanodoti), 

 and those of crocodiles, etc. , are from time to time brought to 

 light. The Wealden rocks occur also on both eastern and 

 western sides of the Isle of Wight, and in Dorsetshire. 



3. Oolites (or Roe-stones) are so named because the charac- 

 teristic limestones of this formation resemble very much the roe of 

 a fish. The small round grains, of which the typical examples are 

 built up, when cut or broken through will be seen to be formed of 

 numerous layers of carbonate of lime, disposed like the coats of 

 an onion, around some central nucleus, generally a grain of sand, 

 a fragment of coral, or the shell of one of the Foraminifera. 

 They are divided into Upper, Middle, and Lower Oolites, and 

 these again are subdivided as follows 



Upper Oolite. 



a. Purbeck Beds, a series of fresh-water, with a few estuarine, 

 or marine beds, which in point of fact connect the deposits we 



