270 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 22, 



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Perna, and a small Neritina and Nerita, 

 underlaid by a hard compact bed of lime- 

 stone without fossils. In other portions 

 of the^section, casts of Cerithium occur 

 in the hard limestone. 



The Talley of the Muhl-thal, between 

 Biebrich and Wiesbaden, represents the 

 upper portion of this formation, and the 

 Littorinella acuta is here so abundant as 

 to constitute almost the entire mass of the 

 rock in many places. With it the Mytilus 

 Brardii is also abundantly found, and a 

 few freshwater shells, as Paludina lent a, 

 Melanopsis, Limnceus, and Planorbis, 

 here make their first appearance, plainly 

 indicating the diminished saltness of the 

 water. 



Another instructive section of the 

 calcareous portion of the Mayence tertia- 

 ries, including the Cerithium-limestone 

 and theLittorinella-limestone,is exhibited 

 in the quarries and other cuttings extend- 

 ing from the fortifications of Mayence, 

 through the village of Weissenau, as far as 

 Oppenheim on the left bank of the Rhine 

 (fig. 11). The three localities of the 

 Kastrich in Mayence, the quarries of 

 Weissenau, and those of Oppenheim will 

 complete our investigation of these beds. 



1. Kastrich in Mayence. This section 

 is exposed in the upper part of the town, 

 in cutting a new road to the fortifications : 

 it represents the upper portion of the 

 Littorinella-limestone, and consists of 

 frequent alternations of thin beds of flaggy 

 limestone wdth arenaceous marly beds. 

 Two species of Littorinella abound in 

 these beds, but they are not less abundant 

 in the arenaceous beds. On the whole, 

 from 30 to 50 feet are exposed here. 



2. Near the village of Weissenau, about 

 one mile S.S.E. from Mayence, extensive 

 quarries have long been opened in the 

 limestone rocks, showing the passage 

 down wardsfrom the Littorinella-limestone 

 to the Cerithium-limestone. The Lit- 

 torinella-limestone appears to thin out 

 gradually as the hills rise towards the 

 S. E. The following sequence, in ascend- 

 ing order, will show how the beds succeed 

 each other : — 



