288 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 22, 



than the lowest bed of a new series ; the latter being in accordance 

 with its true position, the former supposition being at variance with 

 the local facts, and unsupported by satisfactory evidence. 



These are the principal reasons which have induced me to refer 

 the Marine Sands of Weinheim to the Miocene rather than to the 

 Eocene formation, and not on account of any vague numerical pro- 

 portion of forms agreeing more with the recent than with the older 

 beds. No doubt they contain many Eocene forms, but we are not 

 to assume that all life was destroyed at each successive period of 

 change. The old forms were doubtlessly washed into the newly 

 created seas, dead or alive, from the pre-existing Eocene waters ; 

 besides which, many species may have lived through the change, as 

 we find species existing through the whole tertiary period, notwith- 

 standing the many successive changes to which they must have been 

 exposed*. 



Part III. 



On the Ancient Geographical Character and Connection 

 OF THE Sea in which the Marine Fauna of the Mayence 

 Basin was deposited. 



One of the most interesting questions connected with the locality 

 of the Mayence basin, and its marine fauna, is the insulated cha- 

 racter of its position, and its probable channels of communication 

 with the then existing ocean. The opinion generally entertained by 

 the German geologists is, that the region occupied by these marine 

 formations was at the period of their deposition an inland lake 

 (Binnen-See), having no direct communication with the ocean, but 

 containing a somewhat similar fauna in consequence of the saltness 

 of its water. The abundant occurrence of Sharks' teeth of several 

 species, and the remains of Halianassa Collinii in numerous places, 

 sufficiently disprove this hypothesis. Notwithstanding the present 

 difference of levels between the existing sea and the marine beds of 

 Weinheim, amounting to between 500 and 600 feet, and the com- 

 plete insulation of the region, these remains are a convincing proof 



* It must, however, in justice be admitted, that, if this rule is fully carried out, 

 we must not attempt to apply too arbitrarily the nomenclature of one ])Iace to the 

 circumstances of another, when the physical changes which have disturbed the 

 continuity of organic life have taken place at different periods. For example, in 

 Belgium there is no break in the Limburg beds in the continuity of deposition. 

 In Mayence the new system begins with the equivalent of the Middle Limburg 

 series. In another country the physical change took place at a later period, viz. 

 after the Upper Limburg beds or their equivalents were deposited. There we 

 find a regular sequence of beds from the London clay to the Upper Limburg, and 

 then it suddenly ceases, until it is overlaid by diluvial deposits. Here, then, we 

 find that the equivalent of the bed which in the first locality was shown to be the 

 commencement of a new series, and consequently is called Miocene, proves to be 

 in another place the termination of the old series. We have no means of avoid- 

 ing the conviction which forces itself upon us, that we must call it Eocene. Thus, 

 the same beds which I call Miocene in Mayence, may with perfect propriety be 

 called Eocene by I'rof. Forbes, in the Isle of Wight.— July 12, 1854.— \V. J. H. 



