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



question must have been an island or promontory in the tertiary sea ; 

 on further search, I found in the valleys the " loess," resting in 

 general directly on the red sandstone, but occasionally separated from 

 it by a bed of shingle or gravel, in which, in a few places, I found 

 fragments of marine bivalves, amongst which were chiefly Pectun- 

 culus and a single valve of Nucula Lyellii, thus clearly proving even 

 here the existence of a true marine beach. Further west, or inland 

 from the river, the red sandstone is so covered up by "loess" that 

 there was no opportunity of finding any junction between it and the 

 tertiary formation, except beds of small pebbly gravel, probably much 

 more recent. 



B. Tertiary Formation. 



The following series, in an ascending order, is given in all the 

 German works on the Mayence basin* : — 



1 . Marine sand and quartz-conglomerate. 



2. Lower blue brown-coal clay. 



3. Freshwater limestone. 



4. Cerithium limestone, 



5. Littorinella limestone. 



6. Upper blue brown-coal clay. 



7. Upper or leaf-bearing sandstone. 



8. Ossiferous sand. 



• 



The introduction of the Freshwater limestone (No. 3) into the 

 above list appears to me an error. It tends to encourage the idea 

 that we have here a system of alternation of marine and freshwater 

 formations, as in the London, Hampshire, and Paris basins, an idea 

 which the evidence does not in any way justify. I shall therefore 

 omit it in the following description, merely stating where the land- 

 molluscs occur which have given rise to this nomenclature. 



B. 1. Marine sand and quartz-conglomerate. . (List at p. 257.) 



This is unquestionably the lowest member of the tertiary series ; 

 it is frequently non-fossiliferous ; near Weinheim, however, some of 

 the beds contain numerous fossils. The section (fig. 4) exhibits a 

 bed of sand and gravel (B. la) about a foot thick, containing a 

 great number of Sharks' -teeth, some bones of fish, and OstrecB, in 

 many places still adhering to the underlying rock. Above this is a 

 thin bed of fine sand (B. 1 b), overlaid by clays (B. 2), belonging to 

 the blue clay of the brown-coal formation, which on the opposite hill, 

 called the Sommerberg, contains a great abundance of Cerithium 

 margaritaceum and Cyrena subarata. 



Wherever fossils are abundant, as in the neighbourhood of Wein- 



* Walckner's Geognosie, 2nd Edit. Uebersicht der geologischen Verlialtiiisse 

 des Gross-Herzogtluim Hessen, v. Friedr. Voltz, Mainz 1852. Uebersicht der 

 geologischen Verhaltnisse des Herzogthum's Nassau, v. Dr. Frid. Sandberger, 

 Wiesbaden 1847. Untersuchungen iiber das Mainzer Tertiar Becken, v. Dr. F. 

 Sandberger, Wiesbaden 1853 (published and received in London long after the 

 commencement of this paper). 



