Travers. — On the Causes of Volcanic Eruptions. 338 



are sluggish, compared with the fierce action by which disturb- 

 ances are brought about at, or it may be below, the fiery surface 

 of the planet itself." 



I think, indeed, that it may almost be received as a postu- 

 late, that, in whatever manner the cosmical matter of which our 

 globe was formed became aggregated, it must, for a very long 

 period after that aggregation had been completed, have remained 

 iu a condition of intense heat at its surface. 



I have already dealt with this subject in papers on the 

 " Cause of warmer climates which existed in high northern 

 latitudes during former geological epochs," published in the 

 10th volume of the " Transactions of the New Zealand Insti- 

 tute," to which I may refer any person desirous of going more 

 fully into it, and I do this without hesitation, because the views 

 contained in those papers were received with approval by several 

 scientific inquirers of high position and authority in Europe. 

 In the first of those papers I remarked that geologists, including 

 so eminent an authority as the late Sir Charles Lyell, have 

 hitherto treated such speculations as those I have referred to 

 as having only a remote bearing on geology ; but I cannot help 

 thinking, that so long as we continue to recognize the extent to 

 which the surface conditions of the earth have been, and are 

 still being modified by the action of forces operating at great 

 depths below that surface, and especially by such exhibitions of 

 those forces as earthquakes and volcanoes, we are bound to be 

 guided in our inquiries by a regard to those speculations, before 

 we can hope to arrive at any sound understanding of the 

 phenomena in question. 



I must not, however, in justice to Dr. Page, one of the most 

 delightful writers on geology, omit to refer to some remarks 

 which he makes in his " Advanced Test-book," in relation to 

 these speculations. In dealing with the question of the density 

 of our globe, he points out that it cannot, if the law of gravita- 

 tion be acting uniformly towards the centre, be composed 

 throughout of materials in the same condition as those which 

 constitute its crust, because, in that case, a depth would soon 

 be arrived at where the density of ordinary rocks would become 

 so great as to give a mean density much higher than that which 

 its astronomical relations seem to warrant. He also points out 

 that, whilst the ponderable crust, calculating from precession and 

 nutation, cannot be of less thickness than a fourth or fifth of 

 the radius, (being about that assigned to it by Hopkins, as I 

 mention further on,) the interior layers of that crust may con- 

 sist of molten rock-matter, or even rock-matter in a state of 

 vaporiferous incandescence. He then says that, whatever be the 

 exact proportions and conditions of the crust and interior of the 

 earth, we know enough of its temperature to warrant certain 

 general conclusions — namely, that the surface temperature is 



