1819.] Greenough on the First Principles of Geology. 303 



resulted from the rotation of a liquid globe round its axis with a 

 velocity equal to that of the earth. This was demonstrated by 

 Sir Isaac Newton, and has been amply confirmed by the subse- 

 quent labours of mathematicians and astronomers. The specific 

 gravity of the earth may be considered as determined by the 

 experiments of Maskelyne, and the subsequent calculations of 

 Dr. Hutton and Mr. Playfair, and the delicate experiments of 

 Mr. Cavendish, upon which I am disposed to place the greatest 

 reliance. Now as the mean specific gravity of the crust of the 

 earth cannot easily be rated higher than 2*5, it follows as a 

 consequence that the specific gravity of the central parts of the 

 globe must be much greater than 5. It must, therefore, be 

 composed of solid matter of a metallic nature. 



With respect to the nature of the fluid matter which consti- 

 tuted the original globe of the earth, the conjectures of geologists 

 have been various and contradictory. The imagination, unre- 

 strained by the present state of things and the present laws of 

 matter, has been set at complete liberty to wander amidst a 

 chaos of its own creation — 



a dark 



Illimitable ocean, without bound, 



Without dimension, where length, breadth, and heighth, 



And time, and place, are lost. 



Bertrand was of opinion that the earth consisted originally of 

 pure water, and that by the plastic power of nature, this water 

 was gradually converted into the various earths and metallic 

 bodies of which the globe is at present composed. This opinion, 

 compared with which the reveries of the alchymists were modest 

 and plausible, was advanced at the end of the eighteenth century, 

 and by a man who considered himself as profoundly skilled in 

 all the physical discoveries that preceded him. Some circum- 

 stances lead me to suspect that an opinion not very dissimilar 

 was embraced by Werner, or at least by some of the most 

 eminent of his pupils. They nowhere indeed state it in express 

 terms, but they talk of the gradual diminution of water ; and I 

 have been told by some of them, that this liquid would ultimately 

 fail altogether ; or that there was a slow change of this globe 

 from a state of liquidity to a state of solidity — a change which 

 had been going on from the origin of things, and was still in 

 progress. This I consider as tantamount to Bertrand's notion, 

 that the primordial state of the globe was pure water. 



But the most general opinion entertained by geologists is, 

 that all the substances which at present exist in the globe con- 

 stituted a part of it from the beginning ; but that they were at 

 first in a liquid state, and gradually deposited from the watery 

 portion, which still retains its liquidity, partly by crystallization, 

 and partly mechanically. 



From the phenomena of crystallization duly witnessed in the 

 manufactories of the different salts, it is obvious that when solids 



