BY THE EEV. W. B. CLAEKE, M.A., F.G.S., &c. 307 



of the earth's crust is stable, in consequence of the continual 

 motion of the mineral particles. I must now draw upon your 

 patience in order to make a few further practical remarks. 



It might be supposed that most of the phenomena mentioned 

 in this paper have died out, and that no actual instability, such 

 as changes of level, are now going on. 



If it did not carry ine out of my present field altogether, I 

 could easily prove that there are undoubted evidences of 

 considerable changes of level of a quasi-permanent character 

 about Moreton Bay, and in the southern part of this territory, and 

 in Victoria, as well as in South and in West Australia. 



But there are other such changes going on nearer our own 

 homes changes which, however inappreciable by the eye of a 

 common observer, are yet capable of being measured by the 

 delicate contrivances of our colleague, the Government astronomer. 

 He can tell you that there are invisible forces at work which 

 betray their existence by effects that derange his close calculations 

 and defy his grasp. And whether those are all external, as 

 produced by expansion of the rocks by solar heat or contraction 

 by cold, or by the action of rain water filtering through fissures, 

 and so introducing or removing extraneous matter, or whether 

 there is still an expansion or contraction under such normal 

 transmutation as was mentioned when I began, this is undoubted, 

 that the Astronomer does not know at what horizon he can fix his 

 level of the foundation for his instruments, nor does he know 

 whether to-morrow it will be where it was this morning. 



No doubt this is not confined to Sydney Observatory, but 

 is common to others, proving that the fact itself belongs to a 

 general and not to a local law one which is, of course, modified 

 in its application by the peculiar structure, texture, and condi- 

 tions of the rocks of each locality. 



I do not doubt that my first views on this question are sus- 

 tainable, and that, although there may be general causes at 

 work, there are also local circumstances that render the present 

 site of the Observatory an unfortunate one. 



In the days of the late Captain Stanley and Admiral King, I 

 united with those officers in urging the necessity of placing the 

 Observatory upon a wider base of rock, such as the North Shore 



