48 Mr. J. Evans on Geological Changes in the [Mar. 15, 



Sir John Lubbock, however, in common with other astronomers, appears 

 to have regarded the earth as consisting of a sohd nucleus with a body of 

 water distributed over a portion of its surface ; and there can be but Httle 

 doubt that, on this assumption of the sohdity of the earth, the usually- 

 received doctrines as to the general persistence of the direction of the 

 poles are almost unassailable. 



Directly, however, that we argue from the contrary assumption that the 

 solid portion of the globe consists of a comparatively thin, but to some 

 extent rigid crust with a fluid nucleus of incandescent mineral matter 

 within, and that this crust, from various causes, is liable to changes 

 disturbing its equilibrium, it becomes apparent that such disturbances may 

 lead, if not to a change in the position of the general axis of the globe, yet 

 at all events to a change in the relative positions of the solid crust and the 

 fluid nucleus, and in consequence to a change in the axis of rotation, so far 

 as the former is concerned. 



The existence in the centre of the globe of a mass of matter fluid by 

 heat, though accepted as a fact by many, if not most geologists, has no 

 doubt been called in question by some, and among them a few of great 

 eminence. The gradual increase of temperature, however, which is found 

 to take place as we descend beneath the surface of the earth, and which 

 has been observed in mines and deep borings all over the world, the 

 existence of hot springs, some of the temperature of boiling water, and 

 the traces of volcanic action, either extinct or still in operation, which occur 

 in all parts of the globe, afford strong arguments in favour of the hypothesis 

 of central heat. 



And though we are at present unacquainted with the exact law of the 

 increment of heat at different depths, and though, no doubt, under enormous 

 pressure the temperature of the fusing-point of all substances may be con- 

 siderably raised, yet the fact of the heat increasing with the depth from 

 the surface seems so well established that it is highly probable that at a 

 certain depth such a degree of heat must be attained as would reduce all 

 mineral matter with which we are acquainted into a state of fusion. When 

 once this point was attained, it seems probable that there would be no very 

 great variation in the temperature of the internal mass ; but whether the 

 whole is in one uniform state of fluidity, or whether there is a mass of solid 

 matter in the centre of the fluid nucleus, are questions which do not affect 

 the hypothesis about to be considered. 



Those who are inclined to regard the earth as a solid or nearly solid 

 mass throughout, consider that many volcanic phenomena may be accounted 

 for on the chemical theory, which has received the support, among others, 

 of Sir Charles Lyell. But apart from the consideration that such chemical 

 action must of necessity be limited in its duration, the existence of local 

 seas of fluid matter, resulting from the heat generated by intense chemical 

 action, would hardly account for the increase of heat at great depths in 

 places remote from volcanic centres ; and the rapid transmission of shocks 



