EOCENE STRATA. 409 



century and take note of the vague and confused 

 ideas then entertained by geologists as to the arrange- 

 ment and stratigraphical value of the series of deposits 

 that overlie the Chalk. The term London Clay had 

 been applied by William Smith to these deposits from 

 the argillaceous character of their chief member. Sub- 

 sequently various geologists noticed the occurrence of 

 a group of sandy and clayey strata between the main 

 mass of the London Clay and the top of the Chalk. 

 These were grouped together as Plastic Clay and Sand, 

 but their true stratigraphical value and palasontological 

 interest were hardly recognised. In the year 1846, 

 Prestwich published the first of the long series of 

 papers in which he gradually worked out the true 

 relations of the several members of the series, and 

 brought them into relation with their equivalents in 

 France and Belgium. The story of this evolution of 

 clear order out of the confusion that had preceded 

 Prestwich's researches has been well told by Mr 

 Whitaker, who has followed so worthily in the foot- 

 steps of the pioneer whose labours he chronicles. 1 

 Beginning among the cliff sections of the Isle of 

 Wight [9], Prestwich traversed every part of the 

 Hampshire and London basins, recording his obser- 

 vations on copies of the Ordnance maps, and in 

 voluminous note -books. From year to year he 

 communicated his results to the Geological Society, 

 each paper throwing new light on the history of the 

 geological formations, until in 1854 his great essay 

 on the Woolwich and Reading series [23] added the 

 coping-stone to the edifice he had so patiently reared. 

 He showed that between the top of the Chalk and 

 the base of the London Clay a group of strata, which 



1 Mem. Geol. Survey, The Geology of London, vol. i. (1889), p. 88. 



