IV.] THE CHEMISTEY OF THE PRIMEVAL EARTH. 45 



The old question between the plutonists and the neptunists, 

 which divided the scientific world in the last generation, was, 

 in brief, this : whether fire or water has been the great agent 

 in giving origin and form to the rocks of the earth's crust. 

 While some maintained the direct igneous origin of such rocks 

 as gneiss, mica-schist, and serpentine, and ascribed to fire the 

 filling of metallic veins, others the neptunian school were 

 disposed to shut their eyes to the evidences of igneous action 

 on the earth, and even sought to derive all rocks from a primal 

 aqueous magma. In the light of the exposition which I have 

 laid before you this evening, we can, I think, render justice to 

 both of these opposing schools. We have seen how reactions 

 dependent on water and acid solutions have transformed the 

 primitive plutonic mass, and how the resulting aqueous sedi- 

 ments, when deeply buried, come again within the domain of 

 fire, to be transformed into crystalline and so-called plutonic 

 or volcanic rocks. 



The scheme which I have thus sought to put before you in 

 the short time allotted this evening is, as I have endeavored to 

 show, in strict conformity with known chemical laws and the 

 facts of physical and geological science. Did time permit, I 

 would gladly have attempted to demonstrate at greater length its 

 adaptation to the explanation of the origin of the various classes 

 of rocks, of metallic veins and deposits, of mineral springs, and 

 of gaseous exhalations. I shall not, however, have failed in 

 my object, if, in the hour which we have spent together, I 

 shall have succeeded in showing that chemistry is able to 

 throw a great light upon the history of the formation of our 

 globe, and to explain in a satisfactory manner some of the 

 most difficult problems of geology ; and I feel that there is a 

 peculiar fitness in bringing such an exposition before the mem- 

 bers of this Eoyal Institution, which has been for so many 

 years devoted to the study of pure science, and whose glory it 

 is, through the illustrious men who have filled, and those who 

 now fill, its professorial chairs, to have contributed more than 

 any other school in the world to the progress of modern chem- 

 istry and physics. 



