INTRODUCTION. x1 
fossils of the Wealden, Urgonian, and Aptian groups are included 
and not distinguished.” ! 
It will be well, therefore, at the outset to state definitely in 
what sense the term Wealden is used in the present Catalogue. In 
his Memoir on the Weald, Topley expresses the opinion that the 
Wealden and Purbeck strata should be classed together as one 
unbroken series.” This and similar statements by various geolo- 
gists might be quoted in support of a Purbeck-Wealden series, 
and, possibly, such would best represent the true stratigraphical 
relations of the two sets of beds. On the other hand we are not 
concerned here with any critical examination of the geological 
evidence, whether stratigraphical or paleontological; and for the 
present, at least, it will be more convenient to conform to the 
general usage of the term by English geologists, and include 
the Wealden beds in the Cretaceous system to the exclusion of 
the Purbeck. 
In the Report of the British Committee to the International 
Geological Congress of 1888, the Reporters, Messrs. A. J. Jukes- 
Browne and W. Topley,* recommended a general classification of 
the Cretaceous system, in which the ‘‘ Lower series’ of the 
system is defined as comprising the Lower Greensand (Vectian), 
Weald Clay and Hastings Sands; the two latter being bracketed 
together as Neocomian. 
In the correlation table of the Cretaceous system, given by the 
same authors, the Purbeck beds are placed at the base in the 
South-Eastern area. 
In Geikie’s Text-book* the usual classification is adopted, the 
Purbeck beds being regarded as the uppermost members of the 
Jurassic system. 
In this connection it may be of interest to quote the views 
recently put forward by Messrs. Pavlow and Lamplugh in their 
Essay on the Speeton Clay. Their correlation of four zones 
1 Potomac Flora, p. 332. 
2 Weald, p. 321. 
5 Cong. Géol, Int. App. B. Cretaceous, p. 77. 
4 Text Book of Geology, 1893, p. 938. 
