220 Proceedings of the Eoyal Physical Socicfij. 



an earthquake is due, and to the continued action of which 

 is also due the expulsion of volcanic matter to the surface. 

 The discharge of thermal springs, and tlie liberation of 

 their dissolved contents, is yet another result of the same 

 cause. 



At those depths where the pressure is greater, but the 

 quantity of alkaline solutions carried down is less, a slow 

 conversion of the sediments into gneiss takes place. 



Tlie formation of eruptive rocks and gneiss, and, in short, 

 all volcanic and seismic phenomena, are, on this view, 

 traceable, directly or indirectly, to the osmotic transference 

 of alkaline solutions to the sediments below the Transitional 

 Belt of the lithosphere ; that is to say, the chief agent 

 concerned works from above downwards.^ Is anyone pre- 

 pared to demonstrate that such a transference cannot take 

 place ? 



In conclusion, I must frankly admit that some of the 

 foregoing speculations relate to matters concerning which 

 our present knowledge is very imperfect, and is likely to 

 remain so for many years to come. Nevertheless, hypothesis 

 have their uses in geology perhaps more than in any other 

 science. If there are several ways of accounting for a given 

 set of facts, it is at least well to give them all careful 

 consideration, and even those that are least in accordance 

 with the views current for the time being may guide future 

 thinkers to the road that leads to the actual truth. 



^ Since this paper was written, Professor Cargill G. Knott has read a paper 

 on Earthquakes before the Royal Society of Edinburgh (10th July 1899), in 

 which he demonstrates that the interior of the earth is in the condition of an 

 elastic solid. The vieAv of the origin of eruptive rocks here advanced was 

 formally read before the Royal Physical Society on the 19th of April 1899, 

 and was given in outline before the Geological Society of Glasgow on 

 30th May 1898 (see the Glasgow Herald for 31st May 1898). It will be 

 seen that it is in perfect harmony with the view advanced by Professor 

 Knott. 



[The present author communicated an essentially similar view to the 

 British Association, at the Nottingham Meeting, September 1893. Ref. 

 Sec. C, p. 761.] 



