A. VdiKjJuui Jennings — Geology of Bad Nauhelm. 355 



together with Cyrena and Mijt'dus. A specially interesting feature 

 is the occurrence at Bonstadt of porous limestones, evidently formed 

 by incrustation of Algre such as Vaucheria and Charn, with shells 

 bearing a fibrous overgrowth, apparently due to incrustation of 

 Cli(Btopliora. 



Under this lies the ' Cerithienkalk,' with Nerita, Mtjlilus, and 

 Litorina in association with familiar friends of the Hampshire 

 Basin, such as Cerithinm plicatnm, Lam., and Cytherea incrassata, 

 Sow.; passing gradually below into the 'Cerithiensand and Sand- 

 stein.' In this case also there are beds with typical land or fresh- 

 water shells — Helix, Bnlimus, Pupa, and Vlanorhis — but these occur 

 in narrow and unimportant bands, while the associated strata contain 

 not only the brackish-water genera but also such marine forms as 

 Perna, Fasus, and Bulla. 



At the base of the series lies the ' Cyrenenmergel,' a blue or 

 yellow, clayey or sandy deposit, in which the proportion of marine 

 shells is still greater, and includes, in addition to those above 

 mentioned, Nucida, Bnccinwn, and Murex. 



C. The Igneous Series. 



The hills formed by the third group of rocks in the Nauheim 

 neighbourhood have been spoken of as interrupting the continuity of 

 the Tertiary plain, but they do not rise with the striking abruptness 

 of, for instance, the phonolitic Hoheutwiel and neighbouring basaltic 

 hills in Southern Baden. They are low, rounded elevations, except 

 at the north end of the Friedberg outcrop, evidently parts of lava 

 flows rather than denuded volcanic necks. 



The rock itself appears to be a typical dark basalt; often compact 

 and without crystals distinguishable by the eye, but at times with 

 distinct clear green olivines. It is rarely slightl}'^ vesicular,' but 

 shows a slight tendency to columnar jointing in places. Weathering 

 results in the usual pale-brown crust, and often a rough spheroidal 

 structure is revealed in the process. 



Surface accumulations seem everywhere to mask its actual contact 

 with the Tertiary beds, but I have been unable to observe any 

 phenomena of metamori)hism in the latter. This at first sight gives 

 one the impression that the basalts are older than the Oligocene 

 strata, but there is evidence elsewhere to show that such is not the 

 ■case, At Wickstadt, for example, the Litorinellen-kalk is overlaid 

 by basalt. 



IV. The Springs, Borings, and ' Salines.' 



Having thus obtained some insight into the nature of the strata 

 of the district, one is led to consider what is the relationship between 

 the character of these rocks and the presence of the thermal and 

 saline springs to which the locality owes its fame. With this in 

 view it will be necessary to note in some detail the position and 



1 There is a brownish -"jrey scoriaceous rock, which is used iu Nauheim for kerb- 

 stones, etc., but which I could not find m situ. Closer obsurvatiou showed the 

 presence in it of clear blue Hauyn crystals, and it probably comes from the well* 

 known quarries of Niedermendig. 



