^56 M. Bischof oji the Suhterranean Course of Watci-, 



fissures and clefts of mountains. Again, in other localities, such 

 streams of gas are given out from little hollows which are filled 

 with atmospheric water, and where the gas springs present com- 

 pletely the appearance of a mineral spring having an abundant 

 disengagement of gas. It is easy, however, to distinguish such 

 gaseous springs from mineral springs, as the former have no flow- 

 ing of water, and exhibit no iron ochre deposits, or very slight 

 ones, whereas, in most cases, mineral waters which are rich in 

 carbonic acid gas abound also in iron. 



That, in fiict, these gaseous springs are nothing else than ex- 

 halations from mineral springs, flowing at a greater depth in the 

 earth, can be proved by various appearances. In general, they 

 occur at a higher, often at a much higher, level than the rivulets 

 flowing near them, while the mineral waters appear generally at 

 the same or a very little higher level. From hydrostatic laws, it is 

 easy to understand, that, in valleys and near rivulets, springs can- 

 not rise at a much higher level, if the bed of the stream, and 

 also the source of the spring, have Rot a rocky bottom. It is 

 also known, that it is very difficult to force the surface of the 

 spring several feet above the level of the rivulet, in order to se- 

 cure the former from floods. If, then, a mineral spring, rich in 

 carbonic acid gas, ascends obliquely from beneath, and appears 

 at the surface in the bed of a rivulet, at the deepest part of the 

 valley, it may happen that no gas, or only very little, is given 

 out, owing to its already, at an earlier period of the course of the 

 spring, having found a passage of escape through the loose soil. 

 Thus I am acquainted with a plentiful mineral spring, which flows 

 out a few feet above a rivulet from the steep part of the bank, and 

 from which there is not the smallest gaseous exhalation percep- 

 tible. The abundant deposition of iron-ochre shews that the 

 spring must have contained a considerable quantity of gas ; and 

 we have not far to seek for it : for, a few hundred feet above 

 the point at which the mineral spring flows out, at a level about 

 20 feet higher, there is a cavity so filled with carbonic acid gas, 

 that it is only at the risk of losing his life that one can dare to 

 enter it. Probably the Brudeldreis already mentioned is no- 

 thing else than the exhalation of gas from the course of a spring 

 whose origin is to be assigned to the Birresborn mineral spring, 

 which is very near it, and almost at the same level ; and, in the 



