1854.] HAMILTON MAYENCE BASIN. 259 



cipally derived ; and, although the distinction between them was at 

 one time overlooked, these underlying sandstones are mineralogically 

 distinct from the tertiary sands and sandstones. The former are 

 generally thin-bedded, micaceous, and interstratified with bands of 

 black argillaceous shale ; and I have never seen or heard of any 

 fossil remains having been found in them. Of the Sections, that of 

 Weinheim, fig. 4, p. 258, is the most complete. In this section, A 

 shows the Carboniferous sandstone, separated by thin bands of black 

 argillaceous shale ; in which no organic remains could be detected. 

 In places it is much shattered, and traversed by faults and cracks. 

 It is overlaid by the " Marine Sand" (B. I a), which is the lowest 

 member of the tertiary formation of the district. 



We have here abundant evidence that the Carboniferous or red 

 sandstones form the base on which the marine formations of the 

 Mayence basin were deposited ; and they were penetrated in various 

 localities by porphyritic masses previously to the deposition of the 

 marine beds, inasmuch as the latter sometimes repose directly upon 

 the porphyries. These marine beds also mark the commencement 

 of the tertiary period in this district ; and, appear to be confined 

 to its north-western extremity. 



One of the spurs of this red sandstone which forms the nucleus of 

 the range of hills between Alzey and Flonheim, and is penetrated in 

 several places by outbursts of basaltic or porphyritic rocks, extends 

 in a N.E. direction frOm the Donnersberg. The prolongation of 

 this ridge of hills in the same direction, nearly brings us to a con- 

 spicuous hill of red sandstone between Nackenheim and Nierstein on 

 the banks of the Rhine. An excavation near the summit of the 

 table-land near Nierstein, which I visited some years ago, brought to 

 light, in the midst of the opening, a large mass of basalt which had 

 penetrated the red sandstone, and was the probable cause of its up- 

 heaval (see fig. 11, page 270). 



The remarkable appearance of these red cliifs between the hills of 

 white Cerithium-limestone on either side had frequently attracted my 

 attention. They appeared to be overlaid by the Cerithium-limestone, 

 and I therefore determined last summer to visit the locality, ex- 

 pecting there to find a junction-bed between it and the overlying 

 rocks. I was also desirous of ascertaining whether it had formed an 

 island or at least a promontory in the tertiary sea, or whether it had 

 been subsequently elevated. If the latter, it must have brought up 

 the marine sands with it in a tilted position, and I might then expect 

 a rich harvest of new species from this new locality : if an island, I 

 hoped to find traces of the old sea-beach. I proceeded accordingly 

 to Nackenheim, and, ascending the red sandstone hill behind the 

 village, I found it to be principally a micaceous sandstone alternating 

 with marly beds, the sandstone sometimes forming nodules in the 

 marl, and the whole dipping about 10° N.N.E. In some of the 

 ravines behind the village I found that the overlying beds consisted 

 of thick masses of loess instead of limestone ; neither this latter nor 

 the marine sands appeared anywhere to overlie the red sandstone. 

 There was, therefore, everv reason to believe that the red sandstone in 



