X INTRODUCTION. 



Memoir, 1 refers to the Wealden as including the "Weald clay, 

 Hastings sands, and Tilgate beds. In Topley's exhaustive 

 Memoir on the " Geology of the Weald " the area occupied by 

 the rocks in question is spoken of as " one of the best denned 

 geographical tracts in England. Its boundary is the chalk 

 escarpment, which, commencing at Folkestone Hill, near the 

 Straits of Dover, passes through the counties of Kent, Surrey, 

 Hants and Sussex, to the sea at Beachy Head. The oval-shaped 

 area thus enclosed is what geologists have termed the Weald." 2 



The fossils which form the subject of the present Monograph 

 have been collected from rocks included in the Wealden Series, 

 as defined by H. B. Woodward in his " Geology of England and 

 Wales," that is, in the strata which are " developed over a 

 considerable part of Surrey, Sussex and Kent, between Hasle- 

 mere, Hythe and Pevensey; they are also found in Dorsetshire 

 and the Isle of Wight." 



In looking over the literature of Continental or, rather, extra- 

 British Lower Cretaceous stratigraphy, we are met with a difficulty 

 in the use of the terms Wealden and Neocomian. 



In a recent Monograph on the plants of the Potomac Flora 

 of North America, Fontaine has thus referred to the want of 

 a definite understanding as to the significance of these two 

 names: 3 "The two formations which are capable of miscon- 

 ception are the Wealden and Neocomian. By some, the Wealden 

 formation is regarded as an independent group, forming the upper- 

 most member of the Jurassic. Others regard it as a series of 

 beds contemporaneous with a portion of the Lower Neocomian, 

 formed in estuaries and marshes at the time when a portion of 

 the typical Lower Neocomian, which is marine, was being de- 

 posited in the sea. The latter view is the one assumed in this 

 [Fontaine's] Memoir," The term Neocomian is used by Fontaine 

 as including the Urgonian and Aptian of D'Orbigny. He goes 

 on to say: "When, then, reference is made to Neocomian plants, 



1 H. B. Woodward, Geol. England and Wales, 1887, p. 40. 



2 Topley, Weald, p. 1. 



3 Potomac Flora, p. 331. 



