Real and supposed effects of igneous action. 35 1 



II. Mr. Maclure's Letter. 



Remarks on the igneous theory of the earth, in a letter to 

 the editor from William Maclure, dated Jalapa, Mexico, 

 February 8, 1 8'i9. 



Dear Sir — Although M. Cordier sent me his essay upon 

 the temperature of the interior of the earth, being at Har- 

 mony when it arrived at Philadelphia, I had not seen it, until 

 I read the analysis of it in your Journal of October last. As 

 in the pendulum, motion proceeds from one extreme to the 

 other, so it seems that our moral faculties, as well as our 

 physical appetites, must be stimulated by something extra, 

 to afford pleasure, or satisfy curiosity ; not having lately at- 

 tended to the process of fire against water, I was a little sur- 

 prised at the magnitude and respectability of the proofs of 

 the existence of this immense reservoir of melted matter, 

 occupying the earth's centre, with all the operations of the 

 molecules of heat perpetually radiating from it ; my limited 

 experience in the chopping of rocks, having almost convinced 

 me that the two agents, fire and water, had been alternately 

 at work, in covering the primitive, as I thought I could dis- 

 cover rocks, with the volcanic characters, alternating with 

 the transition, secondary and alluvial. Perhaps, when any 

 phenomenon can be accounted for by visible causes, subject 

 to the evidence of all our senses, the inventing of mysteri- 

 ous and hidden agents to account for them, rather augments 

 than removes the difficulties, in which nature has veiled all 

 her actions. The common opinion of mankind, that the 

 sun is the evident cause of the heat of the earth, seems to 

 agree with all experiments made by Perone, Phillips, and 

 others, on the temperature of the ocean ; (as you may see 

 by some memoirs read before the French Institute by Perone, 

 to be found in the Journal de Physique,) proving that heat de- 

 creased in the exact ratio of the distance from the surface, un- 

 til even under or near the equator, the thermometer descend- 

 ed to two degrees above freezing, which, if I recollect well, 

 corresponded with some experiments made on the waters of 

 the lake of Geneva, and had induced me at one time to at- 

 tempt experiments on our lake Ontario, but which I never 

 had an opportunity of trying. At the time those theories 



