STKATA OP THE HAMPSHIKE BASIN. 151 



time so vast a fund of new information has been accumulated con- 

 cerning the age and relations of the equivalent beds upon the Conti- 

 nent, that geologists are now in a very different, and far more 

 favourable, position for estimating the evidence concerning the cor- 

 relation of the various beds than was the case at the time of Edward 

 Forbes's death in 1854. This circumstance, taken in connexion with 

 the fact which I have now established, viz. the error hitherto made 

 in the determination of the order of succession of the beds, affords 

 sufficient warrant for that revision of the classification and nomen- 

 clature of the beds in question which I now propose to make. 



As Professor Huxley has well pointed out, the time is approach- 

 ing when geologists will have to establish two distinct and parallel 

 systems of classification, for the formations of marine and fresh- 

 water origin respectively. In the series of beds which we are now 

 considering, we have such remarkable alternations of marine and 

 freshwater conditions that it will be of advantage to consider the 

 evidence afforded by the study of the marine fauna, and by the 

 freshwater and terrestrial fauna and flora respectively. The earliest 

 classification of the Tertiary strata — that of Lyell — was based en- 

 tirely upon the study of the marine Mollusca; and these forms still 

 constitute the safest guides in correlating the beds over different 

 areas ; but, at the same time, so much attention has of late years 

 been devoted to the study of the freshwater and terrestrial shells 

 (the results of which have been admirably embodied in Dr. Sand- 

 berger's ' Die Land- und Siisswasser-Conchylien der Yorwelt '), that 

 great assistance may be obtained from these forms in the comparison 

 of the strata in different areas. Lastly, the flora and vertebrate 

 fauna occupying the land of the period afford the means of a third 

 series of comparisons. We shall proceed to the study of each of 

 these three kinds of evidence, in the order in which we have enu- 

 merated them, which is the order of their respective importance. 



Confining our attention in the first instance to the forms of marine 

 life, we find that we have three well-marked horizons in the English 

 series which enable us to bring our strata into exact correlation 

 with those of Erance, Belgium, and Northern Germany, and, less 

 directly, with the deposits of the Alps, the Italian peninsula, and 

 Eastern Europe. 



At the base of the Eluvio-marine series lies the richly fossiliferous 

 marine deposit of the Barton Clay. So long ago as 1857, Professor 

 Prcstwich was able to enumerate no less than three hundred species 

 of Mollusca from this formation ; and when all the known forms 

 contained in the numerous collections in this country come to be 

 described, the number of species from this deposit will probably be 

 found to exceed a thousand. 



JN"ow all palaeontologists are agreed that the Barton Clay is repre- 



the British Museum. This splendid collection is so admirably arranged that 

 the work of the palaeontologist who shall deal with these species is greatly 

 simplified ; and it is to be hoped geological literature will soon be enriched by 

 the pubhcation of the as yet undescribed forms by the Palaaontographical 

 Society, or, failing this, by the keepers of the national collection, 



