562 president's address. 



who a few days after the occurrence was fortunate enough to visit 

 and make a personal examination of the scene of disaster, which 

 has been already published in the Sydney Morning Herald. 



This and other similar convulsions probably originate from the 

 generation of molten matter, gases and steam within the great lines 

 of fracture produced by the contraction of the earth's mass conse- 

 quent UDon its cooling. The volcanic cones mark the position of weak 

 points of resistance upon these shrinkage lines, and give way when 

 the expansive forces of the heated matters becomes excessive. It 

 is not improbable that the outbursts may be accelerated by atmos- 

 pheric changes ; for instance when the barometer is low, indicating- 

 less atmospheric pressure over the volcanic region ; or when as 

 Mr. H. C. Russell, our Government Astronomer, pointed out in 

 a letter to the Sydney Morning Herald of 3rd September last, a 

 sudden increase of temperature may affect the earth as it did this 

 year about the period of the meteor shower in August ; for a 

 sudden change in surface temperature must affect the strain under 

 which the earth's surface exists. 



The numerous earthquakes and remarkable tidal phenomena 

 observed throughout Australasia at the time and subsequent to the 

 great eruption at Sunda, were no doubt movements sympathetic 

 with that eruption ; for fractures due to shrinkage or expansion in 

 one part of the earth's mass must affect other parts, but the effects 

 would not be simultaneous, as some of the different rock formations 

 owing to their structures would resist the strain longer than others 

 and thus earthquake movements might be felt at various intervals 

 in different localities. 



Evidences of fracture in the rocks are frequent in almost all the 

 geological formations : I have counted over 30 dislocations in the 

 Wianamatta beds which are exposed in the railway cuttings 

 between Sydney and Parramatta. 



Victoria, especially in the south-western portion, was in the 

 later Tertiary times, the scene of great volcanic activity. No 

 less than 79 extinct points of eruption occur there. Some of 

 these which I have examined are cone-shaped hills, with crater 

 basins, and are built up of basaltic lava, scoria, and ashes. The 



