VI.] THE PROBABLE SEAT OF VOLCANIC ACTION. 61 



by a very small degree, slower than the outer crust.* The 

 same conclusion was subsequently adopted by Hansteen. 



The formation of a solid layer at the surface of the viscid and 

 nearly congealed mass of the cooling globe, as supposed by the 

 advocates of the second hypothesis, is readily admissible. That 

 this process should commence when the remaining envelope of 

 liquid was yet so deep that the refrigeration from that time to 

 the present has not been sufficient for its entire solidification, 

 is, however, not so probable. Such a crust on the cooling 

 superficial layer would, from the contraction consequent on the 

 further refrigeration of the liquid stratum beneath, become 

 more or less depressed and corrugated, so that there would 

 probably result, as I have elsewhere said, " an irregular diver- 

 sified surface from the contraction of the congealing mass, 

 which at last formed a liquid bath of no great depth, surround- 

 ing the solid nucleus." t Geological phenomena do not, how- 

 ever, in my opinion, afford any evidence of the existence of yet 

 unsolidified portions of the originally liquid material, but are 

 more simply explained by the third hypothesis. This, like 

 the last, supposes the existence of a solid nucleus and of an 

 outer crust, with an interposed layer of partially fluid matter ; 

 which is not, however, a still unsolidified portion of the once 

 liquid globe, but consists of the outer part of the congealed 

 primitive mass, disintegrated and modified by chemical and 

 mechanical agencies, impregnated with water, and in a state of 

 igneo-aqueous fusion. 



The history of this view forms an interesting chapter in 

 geology. As remarked by Humboldt, a notion that volcanic 

 phenomena have their seat in the sedimentary formations, and 

 are dependent on the combustion of organic substances, belongs 



* The elevated temperature of the interior of the globe would probably 

 offer no obstacle to the development of magnetism. In a recent experiment 

 of M. Treve, communicated by M. Faye to the French Academy of Sciences, 

 it was found that molten cast-iron when poured into a mould, surrounded by 

 a helix which was traversed by an electric current, became a strong magnet 

 when liquid at a temperature of 1300 C., and retained its magnetism while 

 cooling. (Comptes Rendus de 1'Acad. des Sciences, February, 1869.) 



t Ante, page 39. 



