1854.] HAMILTON MAYENCE BASIN. 255 



of visiting some of the most interesting localities in the district, I 

 propose in the following remarks to lay before the Society the results 

 of my inquiries. The subject is as yet, however, far from being ex- 

 hausted ; many localities require a more searching examination ; the 

 fossils need a more careful and exact comparison with those of other 

 tertiary districts ; and the relations of the formations to those of the 

 north of Germany demand further examination. 



I propose in the following observations, in making which I have 

 been indebted for many valuable suggestions to Mr. R. A, C. Austen, 

 who accompanied me on my last visits to Hochheim and to Alzey, 

 in the first place, to describe the physical features of the district and 

 the stratigraphical position of the different beds ; secondly, to give 

 an account of the palseontological contents of the beds in question, 

 with a special reference to the marine mollusca ; and thirdly, I shall 

 conclude with some remarks on the original position of this marine 

 basin, its probable connection with a former ocean, and the means by 

 which it has been brought into its present relative position. 



Part I. 

 Extent of the Mayence Basin and Stratigraphical 



ACCOUNT OF its DIFFERENT CONSTITUENT BEDS. 



Extent of the area occupied by the Mayence Tertiaries. — The 

 district to which the term Mayence Basin has been applied forms 

 the extreme northern limit of that portion of the great valley of the 

 Rhine, which extends in an almost N. and S. direction from the 

 northern flanks of the Jura to the southern or south-eastern flanks 

 of the Taunus and the Hundsriick (see Map, fig. 1). It is in fact 

 no basin in itself, although, in one sense, the whole of the depressed 

 Rhine Valley, bounded on the W. by the mountains of the Vosges, 

 the Haardt, and Mont Tonnerre, and on the E. by the mountains 

 of the Schwarzwald and of the Odenwald, might not inappropriately 

 be so called. The general character of this valley is well exhibited 

 in the excellent relief-maps of Bauerkeller and of Ravenstein. 



The so-called Mayence basin itself stretches in a general direction 

 from W.S.W. to E.N.E., commencing between Kreutznach and Alzey 

 on the S. side of the Hundsriick, and extending to the N.E. or 

 E.N.E along the S. flank of the Taunus beyond Frankfort and 

 Hanau into the Wetterau, a distance of from 60-70 English miles. 

 Its western limit rests against the Carboniferous formation of the 

 Donnersberg, and the numerous porphyritic outbursts which charac- 

 terize that country ; while its northern beds repose against the talc- 

 slates and sericit-slates of the Taunus. To the S. and E., the forma- 

 tion gradually disappears, partly in consequence of the gentle dip of 

 the beds in that direction, and partly owing to the abrading action 

 of the waters of the Rhine, which now wash its low escarpments or 

 clifi's. To the S., the tertiary formation extends beyond Neustadt 

 to Landau, gradually thinning out, and in a few places only lea\'ing 

 insulated patches adhering to the flanks of the Haardt mountains, 

 and forming steep cliff's or escarpments to the eastward, which will 

 be more distinctly pointed out hereafter. 



