ON THE RECENT VOLCANO OF THE MEDITERRANEAN. 553 



with greatest violence, sandstone barriers are forming- from the deposition, amongst 

 the sand thrown up, of cementing- carbonate of lime, set free from its solution by 

 the diseng-agement of the carbonic acid gas, owing to the agitation ; so, in the greatest 

 depths, deprived of oxygen, vegetable matter may be tranquilly subsiding, and in pro- 

 cess of conversion into beds of coal, for which the temperature of the water at its 

 maximum density, judging from the formation of peat, appears to be most favourable. 



Dr. Daubeny objects to the disengagement of air from water under the circum- 

 stances supposed, subjected to a high temperature under pressure. He says : "Either 

 in this situation the pressure of the superincumbent mass of fluid is sufficient to 

 prevent the conversion of the lower strata of water into steam, or it is not. If it be, 

 this same pressure will enable the water to retain in solution its original quantity of 

 air, or at least the greater proportion of it. If, on the contrary, there be not suffi- 

 cient pressure for the purpose, then no doubt the water will rise up in the form of 

 steam, through the superincumbent mass, along with the air which it had contained ; 

 but, as the temperature of the sea round about the volcano, at least near its surface, 

 is stated by Dr. Davy not to be higher than that of the atmosphere, it is plain that 

 all the steam must become rapidly condensed, and when it returns to its liquid state, 

 there seems no reason why it should not exert its affinity for the air intermixed, and 

 combine with it as before." The greater part of this reasoning relative to the effect 

 of pressure does not appear to me applicable to the phenomenon in question. The 

 volcanic shoal over which the air rose, as already mentioned, was only a few fathoms 

 deep : the circumstances may be considered somewhat analogous to those of an ex- 

 periment in the laboratory for the expulsion of air by boiling water in a retort con- 

 nected with a pneumatic apparatus. In this latter instance, the air is disengaged 

 and the steam is condensed, and yet the air is not reabsorbed ; nor does there appear 

 to me more reason why it should be reabsorbed in the instance under consideration. 

 Supposing a portion of sea water to be converted into steam in the fissures of the 

 shoal, the instant it comes in contact with the cold water it will be condensed, like 

 the steam from the retort, and will be diffused by mingling with adjoining water : 

 but the air disengaged at the same time will not be reabsorbed ; owing to its com- 

 parative lightness, it will immediately ascend, and passing through water already 

 saturated with air, reach the surface. 



Dr. Daubeny supposes that the quantity of air emitted, as observed by Captain 

 Swinburne, bore some relation to that evolved from chalybeate springs ; from whence 

 he infers that " so constant a supply could hardly be derived from such a source as 

 sea water." Were not the quantity very minute, " in small silver threads of bubbles," 

 and varying from time to time in the same place, as Captain Swinburne relates, the 

 objection would have weight. But Dr. Daubeny admits that this minute quantity is 

 very much less than occurs in most thermal springs; consequently the argument 

 loses its force. Relative to the analogy alluded to by Captain Swinburne between 

 the bottom from whence the air rose and a chalybeate spring, it appears to me that 



