x INTRODUCTION. 
Memoir,! 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 defined 
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.” ? 
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:* ‘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, 
‘ H. B. Woodward, Geol. England and Wales, 1887, p. 40. 
2 Topley, Weald, p. 1. 
3 Potomac Flora, p. 331. 
