1854.] HAMILTON — MAYENCE BASIN. 289 



that the sea in which the beds in question were formed must, at the 

 period of their deposition, have been in direct connection with a then 

 existing ocean. The numerous remains of Sharks also show that 

 that ocean was not exclusively an Arctic one ; and even the Halia- 

 nassa tells the same story, its remains having hitherto been found in 

 the Molasse of Switzerland, and at, Malta. On the other hand, the 

 large Cypi-ina rotundata, which can hardly, if at all, be distinguished 

 from the recent C. islandica, shows that we must not look exclusively 

 to a warm or semi-tropical connection. 



The numerous volcanic regions, and the evidence of igneous 

 agency of various periods, by which this district is surrounded, 

 pomt at once to the causes which produced the different changes of 

 relative level by which this connection was broken off. I will here 

 only allude to a few of them. The great volcanic region of the 

 Eifel, lying to the north and north-west of the Hundsriick, which 

 forms the N.W. boundary of our district, is one of the recent results 

 of igneous action. The outpourings of basaltic rocks, which have 

 elevated and broken up the Brown-coal deposits of the "Westerwald, 

 must have been active agents in modifying the physical configuration 

 of this country. The basalts of the Fichtelgebirge, and those in 

 the vicinity of Hanau and of Frankfort, and in the Coal-field of the 

 Wetterau, have probably been equally effective. 



Let us now look at the various tertiary deposits existing in the 

 neighbouring countries, to see how far any connection between their 

 areas and that of the Mayence Basin may be supposed to have 

 existed. 



I. Belgium.' — From the evidence brought forward in the former 

 part of this paper (page 279), there can be no doubt as to the great 

 resemblance between the fossils of the Weinheim sands and those of 

 the Middle Limburg beds, and particularly the so-called Pectunculus- 

 bed, constituting, according to Sir C. Lyell, the upper portion of 

 those Middle Limburg beds. 



The large proportion of identical species in these two formations 

 is alone sufficient to lead to the conviction that some connection must 

 have existed between these two marine basins. Three species of 

 Lamna, viz. L. cuspidata, Ag., L. denticulata, Ag., and L. contor- 

 tidens, Ag., also occur in these beds, which are not only found in the 

 Limburg beds, but in those near Turin. 



II. With the tertiary formations oi France, no special direct com- 

 munication appears to exist, beyond what may be traced through the 

 tertiaries of Belgium. The two districts are here separated by a 

 large tract of intervening mountain-ranges, consisting of Jurassic, 

 liassic, and carboniferous rocks, against which the Weinlieim beds 

 appear to have been subsequently deposited. 



III. Switzerland. — I greatly regret not having yet had an oppor- 

 tunity of seeing Prof. Studer's second volume on the Geology of 

 Switzerland, in which the fossils of the Molasse are worked out*. 



* Since the above was written, the second vohime of Prof. Studer's work has 



