Natural History of Volcanos and Earthquakes. 65 



of the clefts in the whole clay-slate rocks so that the gas will be 

 evolved wherever these clefts are open at the snrface. If these 

 fissures open above the bottom of the valley, and therefore are 

 not filled with water, at least not up to the opening, then the gas 

 will escape from them with a hissing noise. If, on the other 

 hand, they open from beneath the bottom of the valley, and are 

 therefore filled with water, then the gas will escape bubbling 

 through the water, and present entirely the appearance of a min- 

 eral spring. If, lastly, these fissures be covered by alluvium, 

 which, nevertheless, does not form an air-tight covering, then 

 the gas will escape silently from the ground, and such places are 

 recognized from the scanty vegetation which exists there. I 

 know bat one of the first description of fissures in that district, 

 which is found close to the first mineral spring, called Fehlenbor, 

 in the valley of Biirghrohl^ between Tonnisstein and Burgh^ohl. 

 Such a fissure is also found in the Eifel, in the Brudeldreis, as it 

 is called, not far from Biresborn. Fissures filled wiih water, 

 from which gas is evolved, are tolerably numerous, as, for exam- 

 ple m the valley of Burghrokl. I formerly considered these 

 spots (which are constantly met with in the vicinity of the 

 brooks, and consist of little basins filled with water) to be actual 

 mineral springs. If, however, the basin be emptied out, or the 

 water drained off", it is at once perceived that no water springs up, 

 but that merely an escape of gas takes place. I have had an op- 

 portunity of causing such gas-springs to be enclosed, and foimd 

 the disengagement of carbonic acid gas to be extremely copious.* 

 Fissures, covered by accumulated earth, are very frequently met 

 with. If such a place presents a slight excavation, in wiiich the 

 gas collects, suff"ocated animals, as birds, mice, frogs, &c., are 

 commonly found in it. 



As springs run in the most different directions between the 

 surfaces of strata, and through the fissures of the strata, so also 

 do these disengaged gases. I have often had occasion to cause 

 excavations to be made, in places where a scanty vegetation 

 rendered the disengagement of carbonic acid gas at some depth 

 probable. Fissures were often met with in the trass, out of which 

 rose abundant streams of this gas. Sometimes natural canals 

 in the trass were found under a covering of Sph'drosiderit, which 



* Jahrb. der Chemie et Phys. t. Ivi, p. 129. (1829.) 

 Vol. XXXVII, Nu. 1.— July, 1839, bis. 9 



