516 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



The Fossils of the South Downs, or Illustrations of the Geology 

 of Sussex. Like Conybeare, he distinguished two formations, 

 Greensand and Chalk, each of which was divided into sub- 

 groups. The Blue Marl (Gault or Malm) in Mantell's system 

 forms the lowest horizon of the Chalk deposits, and is said to 

 be superposed upon the Greensand formation ; in the latter 

 Mantell includes the various horizons of the true Greensand, 

 the Wealden or Oak-tree Clays, the Tilgate beds, and the 

 ferruginous sand. An atlas, with forty-two plates, contains 

 a geological map of Eastern Sussex and several geological 

 sections, also sketches of characteristic landscapes in the 

 Cretaceous area and illustrations of the fossils belonging to 

 the successive horizons. The best portion of the work is 

 Mantell's description of the three lower horizons of the 

 Greensand formation, which had been in 1828 designated as 

 "Wealden formation" by Martin and Fitton. Mantell after- 

 wards discovered skeletal remains of Iguanodon, Hylreosaurus, 

 and other reptiles in the Tilgate strata, and otherwise con- 

 tributed very greatly to our knowledge of the fauna and flora 

 of the fluviatile Wealden formation. 



In Yorkshire the lower greensand, and perhaps also the 

 Wealden horizon, is replaced by clays and oolitic ironstones, 

 to which J. Phillips gave the name of Speeton Clay. The 

 parallelism of the argillaceous and ferruginous series of York- 

 shire with a similar marine facies pf Neocomian deposits in 

 Russia, has recently been made the subject of combined 

 investigations by Lamplugh and Pavlow. 



W. H. Fitton was the first to arrive at definite results re- 

 garding the stratigraphy of the older Cretaceous deposits in 

 England. His paper, entitled " Observations on some of the 

 Strata between the Chalk and the Oxford Clay," was read at 

 the Geological Society in 1827, but not published until 1836 

 in the Transactions. In it Fitton retained both sub-divisions, 

 Chalk and Greensand, but assigned the Upper Greensand 

 layers of Blackdorn, etc., to their correct stratigraphical 

 position, and recognised the Lower Greensand as the base- 

 ment beds below the Gault. Numerous sections, a geological 

 map, and lists of fossils accompany the accurate and funda- 

 mental observations of this geologist. A combined work, 

 published by Buckland and De la Beche in 1830, contains 

 valuable information regarding the stratigraphy of the Cre- 

 taceous formation in Dorsetshire. 



