Presidential Address. 213 



character. One of these relates to the rapidity or slowness 

 of such movements, and the consequent degree of intensity 

 of the heat developed, as a possible cause of metamorphism 

 of rocks. Another has reference to the possibility of 

 changes in the equilibrium of the earth itself as resulting 

 from local collapse and ridging. These questions in con- 

 nection with the present dissociation of the axis of rotation 

 from the magnetic poles, and with changes of climate, have 

 attracted some attention, 1 and probably deserve further con- 

 sideration on the part of physicists. In so far as geological 

 evidence is concerned, it would seem that the general asso- 

 ciation of crumpling with metamorphism indicates a certain 

 rapidity in the process of mountain-making, and consequent 

 development of heat ; and the arrangement of the older rocks 

 around the Arctic basin forbids us from assuming any ex- 

 tensive movement of the axis of rotation, though it does not 

 exclude changes to a limited extent. I hope that Professor 

 Darwin will discuss these points in his address to the Phy- 

 sical Section. 



I wish to formulate these principles as distinctly as pos- 

 sible, and as the result of all the long series of observations, 

 calculations, and discussions since the time of Werner and 

 Hutton, and in which a vast number of able physicists and 

 naturalists have borne a part, because they may be con- 

 sidered as certain deductions from our actual knowledge, 

 and because they lie at the foundation of a rational physical 

 geology. 



We may popularise these deductions by comparing the 

 earth to a drupe or stone-fruit, such as a plum or peach, 

 somewhat dried up. It has a large and intensely hard stone 

 and kernel, a thin pulp made up of two layers, an inner 

 more dense and dark-coloured, and an outer less dense and 

 lighter-coloured. These constitute the under-crust. On the 

 outside it has a thin membrane or over-crust. In the pro- 

 cess of drying it has slightly shrunk, so as to produce ridges 

 and hollows of the outer crust, and this outer crust has 



1 See recent papers of Oldham and Fisher, in Geological Magazine 

 and Philosophical Magazine, July 1886. Also Peroche, Revol. Po- 

 laires. Paris, 1886. 



