426 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



are associated with one another in such a way that they may 

 be regarded as having taken origin simultaneously." Hum- 

 boldt admitted that fossils were useful in identifying the age 

 of certain rocks, but thought they could not supply a sufficient 

 basis for establishing a chronological succession of the forma- 

 tions and the different horizons in the formation. 



In the year 1822, Conybeare 1 and Phillips published a work 

 on the geology of England and Wales, which, although it has a 

 distinct local colouring, gives a fairly complete representation 

 of the geological knowledge of the sedimentary rocks at 

 the time. The two authors applied throughout the work 

 William Smith's principle of determining the age of the 

 rocks upon the evidence of the fossils contained in them. 

 The introduction contains a succinct historical sketch of the 

 progress of geology in Great Britain. The stratigraphical part 

 begins with a short description of the Alluvium and Diluvium, 

 then enters in fuller detail into the consideration of the 

 " Formations above the Chalk," the formations that were 

 afterwards grouped as Tertiary. Conybeare and Phillips dif- 

 ferentiated the successive horizons in this group, upon the 

 basis of Webster's and Buckland's researches, into four hori- 

 zons : 



Upper Marine Formation (Crag and Bagshot Sand). 

 Fresh- water ,, 



London Clay ,, 



Plastic Clay 



Between these and the Oolite formation Conybeare and 

 Phillips distinguished two main sub-divisions in the Cretaceous 

 formation : 



Upper Cretaceous System, comprising the Chalk deposits. 

 Lower Cretaceous System, comprising Chalk Marl, Green- 

 sand, Weald Clay, and ferruginous sand. 



The sub-division of the Oolite formation was carried out on 

 the basis of W. Smith's observations. Conybeare and Phillips 

 distinguished four main divisions : 



Upper Oolite System, with (a) Purbeck Series, (&) Port- 

 land Oolite, (c) Kimmeridge Clay. 



Middle Oolite System, with (a) Coral Rag, () Oxford 

 Clay. 



1 William Daniel Conybeare, born 1787 in Bishopsgate, studied in 

 Oxford, entered the Church and became Dean of Llandaff; died in August 

 1857- 



