part 1] AJSTNIYERSARY ADDRESS OF THE PRESIDEJVT. Ixvil 



These are some of the considerations which have led nie to believe 

 that Col. Harboe's interpretation is, in the main, well founded, and 

 if it be true that earthquakes of great extent are due to systems of 

 fracture, or analogous disturbance, ramifying over, and pi'actically 

 co-extensive with, the seismic areas of the eartliquakes, that is, over 

 areas of which the dimensions in an^^ direction may be measured 

 in hundreds of miles, it becomes more than ever necessary to 

 recognize that the earthquake origins cannot be the result of 

 processes and disj^hicements, recorded, and indicated, by the 

 tectonics of the surface-rocks. The real and ultimate origin must 

 be more deep-seated, and involve either a dispkicement of, or a 

 change of volume in, the material underlying the outer crust. 



This is no occasion to enter into detail, and so I have merely 

 indicated the general character of the studies which ha\'e gradually 

 forced me to the conclusion that great earthquakes, and also to a 

 great extent those lesser ones which are commonly classed as 

 tectonic, do not owe their origin to the tectonics of the outer 

 crust, but to processes and changes which take place in the material 

 below it. What these processes may be we cannot know, with the 

 certainty which comes from direct observation, for such knowledge 

 as we think we have comes from inference, deduction, and, to 

 some extent, simple assumption ; but suggestions have been made 

 which possess a considerable degree of probability. Among these, 

 and especially apposite to present considerations, may be placed 

 Dr. L. L. Termor's studies of the changes in minerak aggregation 

 which may take place in the solidification of a magma ; he has 

 suggested that the determining factor m deciding the form in 

 which the rock finally solidifies, is the inter-relation of pressure 

 and temperature, and has sliown that the change of volume, 

 consequent on the change from one mode to another, may amount 

 to over 20 per cent, in extreme cases. Mr. W. H. Goodchild 

 has also studied the subject from another point of vie\\'. and 

 suggested that some of the changes, especially the sej^a ration of 

 metallic sulphides, take place with great, even explosive, rapidity. 



I may point out that we have, within our common everyday 

 experience, familiar analogies to those changes which are presumed 

 to take place in the material below the outer crust. Every time 

 that we fire a gun, the ini])act of the hammer starts a change, by 

 which the chemical elements, forming the material of the chai-ge, 

 pass from one mode of combination to another in whicli they 

 occupy a vastly greater space, and in so doing give rise to the 

 pressure by wliich the projectik>, whether ball or shot, is proi)ened. 



