Yol. 57.] ANNIVERSARY ADDRESS OF THE PRESIDENT. IxiX 



of viscosity of quartz and its slight tendency to crystallize. A 

 similar view has recently been advocated by Prof. Joly. Durocher 

 replies to Scheerer's argument derived from the absence of quartz in 

 obsidians, by pointing to its presence in trachytes, and attempts, 

 somewhat unsuccessfully, to explain away the presence of the 

 pyrognomic minerals. In his criticisms of Scheerer's views as to 

 the amount of water present in granite he is often effective, for he 

 shows that sufficient allowance had not been made for the effects of 

 alteration. 



Scheerer's view became the popular one, and is now generally 

 held. It was greatly strengthened by Dr. Sorby's discovery of the 

 widespread distribution of liquid cavities containing water in the 

 quartz of granites, and by the well-known synthetic experiments 

 of Daubree and others. The failure of all attempts to produce 

 granite is also still felt to be a strong argument against the theory 

 of dry fusion. 



Scheerer concludes the discussion with some observations which I 

 cannot refrain from quoting. He says : — 



' To avoid misunderstanding, I desire to make some remarks on the value 

 which I attach not only to my theory of the origin of granite, but also to 

 geological theories in general. I am far from believing that the igneous 

 theory, which M, Durocher defends with so much vigour, is finally disposed 

 of, or that my theory is completely satisfactory. Such definite conclusions 

 cannot be reached in the present state of our science. More than one point 

 of view is possible on almost every subject of this kind, and thus it must ever 

 be, for mathematical certainty is unattainable. 



' A short time ago it seemed as if the Neptunean theories had completely 

 abandoned the field in favour of those volcanic theories which appeared so 

 absurd to our ancestors. Now the Neptunean theories are beginning to show 

 signs of life. I have endeavoured to conciliate the two sister-enemies by 

 suggesting that water may play an important part in the formation of fused 

 rocks. ... I do not pretend, however, that my theory is unassailable, or tbat 

 it has been absolutely demonstrated. ... In my opinion a geological theory 

 should not be considered as absolute ; but it becomes probable when a con- 

 siderable number of facts group themselves around it, and its degree of 

 probability can be measured by its power of assimilating the new facts brought 

 to light by the progress of science.' 



These are wise words, and may well be remembered when dif- 

 ferences of opinion tend to become sharply accentuated. The path 

 of science is littered with discarded theories, and this fact should 

 serve to remind us that ' we are none of us infallible, not even the 

 youngest.' 



In the discussion between Scheerer and Durocher attention was 



VOL. LVII. / 



