1854.] 



HAMILTON — MAYENCE BASIN. 



267 



two formations pass gradually into each other, and should only be 

 looked upon as subdivisions of the great calcareous deposit, formed 

 during the period when this lacustrine basin was passing from a 

 brackish to a freshwater condition. 



The following section, fig. 9, taken at Hochstadt, near Hanau, will 

 show how the two formations, extending from the lower to the upper 

 blue clay, pass into each other. 



Fig. 9. — Section of the Cyrena Clay (B. 2.), Cerithium and 

 Littorinella Limestones (B. 3, B. 4), and the Upper blue Clay 

 (B. 5), at Hochstadt . 



Plain. 



B.4 



B. 3. 



1. (B. 2.") Blue dsiy (unterer blauer Letten) without fossils, said to 

 rest immediately on the red sandstone (Bunte7'-Sandstein or rothe- 

 todte-liegende). The pits where this blue clay had been dug out are 

 at the foot of the hill below Hochstadt, but had all been filled up 

 before I was there, so that I was indebted for my information to 

 M. Roessler of Hanau, who accompanied me to the spot. 



2. (B. 3.) Compact blue limestone passing into yellow. This bed 

 is also unfossiliferous and slightly bituminous. 



3. Hard limestone, occasionally nodular and concretionary, con- 

 taining Littorinella and Dreissena Brardii. 



4. (B. 4.) Limestone of a similar character, with numerous Litto- 

 rinellce and Helices of various species. "We did not find Dreissena in 

 this bed ; but bones are said to have been occasionally found in the 

 lower portion of it. It is the occurrence of these numerous HeliceSy 

 in particular spots of this formation, which has led the German geo- 

 logists to call it a freshwater limestone, but there seems to be no 

 sufficient ground for such an assumption. No freshwater shells are 

 found in it, neither Planorbis, Limnceus, nor Paludina. It is evi- 

 dently a continuation of the brackish-water formation, into which 

 land-shells have been drifted by the rivers. The abundance of these 

 molluscs in particular spots has been accounted for by supposing 

 them to have been deposited in those places where a great river, 

 flowing into the brackish-water lake, impinged against particular 

 promontories more exposed to the currents of fresh water. Sup- 

 posing this ancient tertiary river to have occupied the bed of the 

 present Maine, issuing into the plain (then a lake) from the narrow 

 defiles near AschafPenburg, the current would naturally deposit on 

 the opposite bank the land-shells brought down by freshets from the 



