280 Remarks on Volcanoes. 



from the existence of zeolites in the midst of rocks of sup- 

 posed igneous formation, as the readiness with which these 

 minerals part with their water, seemed inconsistent with the 

 supposition of their originating at a high temperature. 



This was got over by supposing such minerals to have been 

 formed under a pressure sufficient to prevent the water from 

 escaping, and hence the Vulcanists were in some cases driven 

 to assume pressure where none could be shewn to have ex- 

 isted. 



But Bunsen has relieved them from this embarrassment by 

 demonstrating that zeolites may be generated by fusing lime 

 and silica with an excess of caustic potass, without any pres- 

 sure at all ; and that by this method crystals may be pro- 

 duced at a red heat containing water, of which, however, the 

 greater part is disengaged at a temperature not exceeding 

 228°, when the substance is detached from the crucible in 

 which it had been formed. 



Professor Bunsen has also, by a series of decisive experi- 

 ments, removed all doubts as to the nature of the aeriform 

 bodies which are disengaged from volcanoes, and has fully sub- 

 stantiated what my own observations, and those which I had 

 collected from various other sources, led me to infer, namely, 

 that inflammable gases, made up either wholly or in part of 

 hydrogen, are amongst the most constant concomitants of vol- 

 canic action in all its various phases. Nitrogen also, often 

 unaccompanied with oxygen, seems to be as common in the 

 fumaroles of Iceland, as I have found it to be in the thermal 

 springs of other volcanic regions. 



And with respect to the origin of these gases, Bunsen most 

 satisfactorily refutes the idea of his countryman Bischoff, who 

 refers them to the spontaneous decomposition or dry distilla- 

 tion of organic matters, shewing that when this process takes 

 place, nitrogen is invariably accompanied with marsh gas and 

 other hydrocarbons which are never present in volcanoes. 



He accordingly expresses his decided opinion that the ob- 

 jections which have been supposed to be fatal to the old vol- 

 canic theory of Davy, entirely lose their value after these re- 

 sults. " For if," he remarks, " in the spirit of this theory it 

 is assumed that the lavas, and the phenomena of ignition ac- 



