98 Rev. 0. Fisher — " Uniformity " and " Vulcanicity." 



fallacious results, because the facts of Geology were then little 

 known. Speculation preceded observation. But we have now 

 immense stores of observations, by which speculation may be guided ; 

 and if speculators are not so perfectly acquainted with these as 

 observers are, the latter can check them, and they are, as Mr. Ward 

 has proved himself, fully equal to the task. 



To follow speculation to its legitimate conclusions, some know- 

 ledge of mathematics, physics, and chemistry are needed, as Mr. 

 Mallet truly tells us. The philosophical method appears to be, in 

 Geology as in other kindred sciences, to start with a probable 

 hypothesis, and, following it to its necessary consequences, to in- 

 quire whether these harmonize with observed facts. It is here that 

 mathematics finds its proper field. That science is a mode of 

 reasoning, unerring in its methods, but wholly dependent for the 

 truth of its results upon the premisses, assumptions, and limitations, 

 according to which the inquiry is conducted. If the result turns 

 out to be erroneous, it is not the method which ought to bear the 

 blame, but the original hypotheses. 



Mr. Mallet has lately cast down his gage with so loud a ring that 

 he has arrested general attention, and his theory of Vulcanicity is so 

 ingenious and so bold, that it appears to have thrown many minds 

 into one of two states, which are, either of them, unfavourable to 

 calm inquiry. Those whose views are called in question reply in a 

 spirit as eager as that in which they have been challenged ; while 

 others, charmed with the novelty and seeming simplicity of the 

 theory, embrace it as of course. For my own part I cannot say that 

 my mind is at all made up upon the subject ; and it needs more 

 study than I have been able to give, before I can persuade myself 

 that I even understand his argument. But I am free to allow that 

 I consider Mr. Mallet's paper in the Philosophical Transactions an 

 important work. The mere experiments upon the resistance which 

 different rocks offer to crushing, the elaborate tables founded upon 

 them, the investigations on the fusion of slags, and their contraction 

 in cooling, with the tabulated results — all these, apart from any 

 conclusions drawn from them, are of very great value. Whether 

 the theory of Vulcanicity, which the author builds upon these experi- 

 ments, is their legitimate outcome, is the point really in question. 

 Yet as far as I have seen, it has been barely touched by his critics. 

 The question when simply stated appears to be this. Is the super- 

 heated interior of the earth so deeply buried at the present time as 

 to render it highly improbable that volcanos should be channels of 

 communication between it and the surface? Mr. Mallet believes 

 that it is too deeply buried, and suggests a secondary cause, due 

 ultimately, nevertheless, to the presence of a heated interior, and so 

 accounts for volcanic action. Mr. Scrope, on the other hand, in- 

 quires, why, admitting a heated interior, should it be sought to 

 bring in a secondary cause in order to account for the superficial 

 manifestations of its presence. This query is clearly pertinent. 

 Yet, for all that, it may have to be answered that such a secondary 

 cause is necessary. So the question might be asked and answered, 



