Natural History of Volcaiios and Earthquakes, 65 



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



4 



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 np to the opening, then the gets 



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 

 Imow but one of the first description of fissures in that district, 

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

 in the valley of Bitrghrold^ between Tonnisstcin and BtirghrohL 

 Such a fissure is alSo found in the Eifel^ in the Briidcldreis^ as it 

 is called, not far from Bireshorn. Fissures filled with water, 

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

 ple m the valley of BnrghrohL I formerly considered these 

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

 brooks, and consist of httle 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 0i> 



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

 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 which the 

 gas collects, suffocated 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. 1 have often had occasion to cause 

 excavations to be made, in places where a scatity 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 



« Jabrb. der Chemie et Phys t. Ivi, p. 129. (1829.) 

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



