360 A. Vaughan Jennings — Geology of Bad Nauheim. 



of salt solution under the microscope. The brine in the tank at 

 this point is clear, and contains but little life. A few floating 

 patches of a green alga {Bhizoclonium ?) are, however, generally 

 present. 



In the last or most westerly tank the appearance is very different. 

 The water has a stagnant and turbid aspect, and is often covered with 

 bacterial scum. Dense masses of Vaucheria form rounded cushion- 

 like growths at the bottom, and the filaments become completely 

 incrusted except at the growing tips. If these had been formed 

 under natural conditions, and subsequent infiltration by lime had 

 occurred, a formation would be produced which can be paralleled 

 by the oblique limestones already referred to as found at Bonstadt 

 in the Northern Wetterau. 



The algal masses are crowded in the spring by larval cases of 

 a dipterous insect, some half an inch long, and later in the year the 

 surface of the water swarms with small black flies. As the cases 

 become similarly incrusted they would contribute to rock formation 

 and produce a rich 'indusial' limestone deposit. As the water here 

 contains a high percentage of salts the luxuriant growth of these two 

 organisms is remarkable ; and doubtless microscopic study, which 

 I was unable to undertake, will reveal other forms of interest. 



V. Geological Problems involved. 



Leaving here this brief description of the distribution of the 

 various formations and of the general character of the springs 



FiQ. 4.— Geological explanation of the data furnished by the borings as given by 



Dieffenbach (Desc. of Geol. Map of Hesse, Darmstadt, 1856). 



B. Blattersandstein. L. Litorinellen-kalk. 



T. Taunus-quarzit. S. Spiriferen-sandstein. 



0. Orthoceras-schiefer. S.k. Stringocephalen-kalk. 



and bonngs, we may turn, in conclusion, to some consideration of 

 the geological problems involved. The chief of these may be 

 enumerated as follows:— (a) the underground structure as indicated 



