Note by Dr Daubeny. I59 



materially enhanced, if the specific gravity of the ejected 

 material had chanced to be only 2.39, instead of being, as it 

 now turns out, 3.09, and this, as we have seen, is the whole 

 amount of the difference, between the density of the lava 

 itself, and that of the metals which are present in its com- 

 position. 



I find, also, that, by my haste to reply to Bischof 's objec- 

 tions, I have been prevented from noticing certain passages 

 which appeared, since my remarks were penned, in the con- 

 cluding portion of the Professor's memoir, having reference 

 to my own views and arguments. I am not, however, dis- 

 posed at the present moment to enter further at length into 

 this discussion, and will only remark, that Dr Bischof is cor- 

 rect in concluding, that the chemical processes which I assign 

 as the cause of the temperature of thermal springs, are not 

 imagined to be going on near the surface of the globe. 



If there be reason for concluding that volcanic phenomena 

 result from certain chemical processes, the latter must at 

 once lie very deep, and must take place throughout the globe 

 very generally, although in various degrees of intensity. 



It does not, therefore, follow from this, that volcanos, which 

 constitute only the most violent phase of activity of which 

 these operations ai'e susceptible, should be themselves uni- 

 versally distributed ; but it does appear a natural consequence 

 that thermal springs, which ai'e the results of a more languid 

 state of action of the same kind, should be as generally dif- 

 fused, as we find them to be. Not, indeed, that the processes 

 alluded to are necessarily going on everywhere, in the very 

 spots from which thermal springs issue, but that a general 

 elevation of temperature has been imparted to the materials 

 of our globe at a certain depth beneath its surface, owing to 

 those operations of a volcanic nature which are here and there 

 in progress. 



With regard to the precise nature of the chemical processes 

 which give birth to volcanos, I have always spoken with cau- 

 tion, studiously distinguishing between the degree of proba- 

 bility belonging to that part of the hypothesis in question 

 which asserts the fact of the general absorption of oxygen gas 

 throughout the interior of the globe, and that which under- 



