186 SEPARATION OF EOCENE AND MIOCENE STRATA. [Ch. XV 



Miocene. Dr. Sandberger divides the sti-ata of the Mayence basin into 

 two sections, an older and a newer, the former confessedly the equiva- 

 lent of the Limburg (or Hempstead) beds, while in tlie upper he finds 

 some fossil remains, which appear to liim to have a more modern char- 

 acter. But when we separate from this higher division the sands of 

 Eppelsheim, containing bones oi Deinotherium and Mastodon longirostris^ 

 which are most probably of falunian age, the rest of his upper series 

 may be as old as the Limburg beds, though, for want of good sections, 

 there is much obscurity in regard to the grouping of the beds. Dr. 

 Sandberger, how^ever, gives a list of twelve shells, besides some teeth of 

 fish and other fossils, which are common to the Mayence basin and the 

 Hesse-Cassel sands. ISTow the latter were classed as Subapennine or 

 Pliocene by Philippi, and, although we have as yet no sufficient data 

 ^or determining their true age, appear clearly to belong to a more mod- 

 ern fauna than that of the Mayence basin. If such a relationship could 

 be established between the two as to indicate a passage from the Hesse- 

 Cassel fauna to that of the Mayence beds, this fact would doubtless go 

 some way towards bearing out the views of the author. 



The reader has probably by this time begun to perceive that one 

 cause of embarrassment, experienced in the classification of these ter- 

 tiary formations, arises from the discovery of several missing links in the 

 chain of historical records. I may remind him that for more than 

 tvt'enty years I have advocated in the Principles of Geology the doctrine 

 that there has been a continual coming in of new species, and dying oui. 

 of old ones, and a gradual change in the physical geography and cli- 

 mate of the earth, and not such a reiteration of sudden revolutions in the 

 animate and inanimate worlds, as was once insisted upon by many Eng- 

 lish geologists of note, and is still maintained by not a few of the most 

 distinguished continental writers. "When, therefore, I proposed in 1833 

 the term Miocene for the faluns of Touraine, the fossil shells of which, 

 according to the determination of M. Deshayes, contained an admixture 

 of about seventeen in the hundred of recent species, I foretold that from 

 time to time new sets of strata would come to light, and require to be 

 intercalated between those already described, and in that case that the 

 fossils of newly-found beds would " deviate from the normal types first 

 selected, and approximate more and more to the types of the ante- 

 cedent or subsequent epochs." According to this view^, it was obvious 

 from the first that the oldest Miocene records, whenever they were 

 detected, would not be easily distinguishable from the youngest 

 members of the Eocene series, especially in the proportion of the 

 living to the extinct- species of fossil shells. The importance, indeed, 

 of tho latter test must diminish rapidly the more we recede from 

 the Pliocene and approach the Miocene, and still more the Eocene for- 

 mations, although it is never without its value, and often furnishes 

 the only common standard of comparison between strata of very distant 

 countries. 



I make these allusions to show that I am by no means unprepared 



