1854.] HAMILTON — MAYENCE BASIN. 2/3 



Although this Ossiferous Sand is unquestionably more recent than 

 the underlying formations ; and although it may be difficult, from 

 from want of proper means of comparison, to fix its exact relative age, 

 yet the great analogy between the numerous land and freshwater mol- 

 luscs found in the underlying Littorinella and Cerithium limestones 

 with those now living in the southern regions of Europe will justify 

 us in assuming that the terrestrial and climatological conditions of life 

 were not very different from those now existing, and that the super- 

 ficial surface of the ground had already assumed its present form and 

 configuration. 



Part II. 



On the Zoological Characters and Age of the Marine 

 Molluscous Fauna of the Mayence Basin. 



Having endeavoured in the preceding statements to describe the 

 geographical position and the physical features of the various strata 

 of the Mayence basin, with their relative succession and superpo- 

 sition, I now propose to allude to their paleeontological contents, and 

 to point out their analogies with the tertiary deposits of neighbour- 

 ing regions, so far as they have yet been examined, with the view of 

 ascertaining their true position in the tertiary series, and the period 

 to which they should be referred. 



Although I have succeeded during several excursions in collecting 

 a considerable series of the fossils of this region, I could not ex- 

 pect to be so successful as those who, from long residence in the 

 neighbourhood, have such constant opportunities of collecting, as the 

 geologists of Wiesbaden, Mayence, Hanau, &c. ; and who, in ex- 

 tending their knowledge of the fossil contents of the Cerithium 

 and Littorinella limestones, had the additional advantage of exa- 

 mining the ground during the construction of the Mayence, Wies- 

 baden, and Frankfort railways. I am therefore compelled to have 

 recourse to the lists of fossils published by these observers ; amongst 

 which I may particularly mention those of M. Walckner and of 

 Dr. F. Sandberger, to which I am most indebted. 



Although the fossil contents of the overlying brackish and fresh- 

 water formations are not without considerable interest in reference to 

 the question of Age now immediately before us, their importance is 

 but small, when compared with that of the underlying Marine Sands. 

 It is the marine fauna to which we have principally to look, as the 

 key of the whole question. Wherever this bed shall be placed, all 

 the others follow immediately and without interruption. Their 

 superposition is self-evident, and the gradual passage from one into 

 the other is proved by mineralogical no less than by palseontogra- 

 phical evidence. In this marine sand, principally derived from the 

 disintegration or abrasion of the previously existing and underlying 

 red or carboniferous sandstones and shales, we have the evident com- 

 mencement of a new state of things, the basis of a new formation ; we 

 here see the first proofs of a new deposit thrown down upon a new 

 sea-bottom, when, after a sudden change in the relative levels of land 



