Geological Society : — Anniversary of 1839. 235 



we suppose, as Mr. Darwin supposes, a vast portion of the earth's 

 crust, the whole territory of ChiU for example, to rest on a lake 

 of molten stone, there is considerable force in M. de Beaumont's 

 argument : — that when such a fluid is raised to the top of a moun- 

 tain ten or twenty thousand feet high, the pressure upon the crust 

 which is in contact with the fluid must be more than a thousand 

 atmospheres ; and who, he too asks, flatters himself that he knows 

 enough of the interior machinery of volcanos, to be certain that 

 this vast pressure, acting upon a large surface, may not, by some 

 derangement of its safety valve, the volcanic vent, produce effects 

 to which we cannot assign any limit? 



In speaking of Mr. Darwin's researches I cannot refrain from 

 expressing for myself, and I am sure I may add for you, our dis- 

 appointment and regret that the publication of Mr. Darwin's jour- 

 nal has not yet taken place. Knowing, as we do, that this jour- 

 nal contains many valuable contributions to science, we cannot 

 help lamenting, that the customs of the Service by which the 

 survey was conducted have not yet allowed this portion of the 

 account of its results to be given to the world. 



Although not communicated to us, but to our Alma Mater the 

 Royal Society, I may notice Mr. Hopkin's endeavors to throw 

 light upon such subjects as this by the aid of mathematical rea- 

 soning. The researches of Mr. Hopkins respecting the effects 

 which a force from below would produce upon a portion of the 

 earth's crust, have already interested you, and would be of still 

 greater value if the directions of faults and fissures which result 

 from his theory did not depend very much upon that which in 

 most cases we cannot expect to know, the form of the area sub- 

 jected to such strain. Mr. Hopkins has since been employing 

 himself in tracing the consequences of another idea, truly ingeni- 

 ous and philosophical, and which a person in full possession of 

 the resources of mathematics could alone deal with. Some of 

 the effects which the sun and moon produce upon the earth (as 

 the precession and nutation,) include the attraction of those bod- 

 ies upon the interior portion of the earth, and have hitherto been 

 deduced from the theory by mathematicians, upon the supposition 

 that the earth is solid. But what if the central portion of the 

 earth were fluid ! What if it appeared, by calculation, that the 

 fluid internal condition would make the amount of the precession 

 of the equinoxes, or of the nutation of the axis, different from 



