ANNIVEE8ART ADDRESS OF THE PRESIDENT. 6 1 



With these preliminary remarks, for which I trust I may bo par- 

 doned, as they are the outcome of an experience gained during some 

 eight years in your service and some fourteen in petrological work, 

 I turn to the special subject which I intend to discuss briefly to-day 

 — the classification and structures of the igneous rocks. 



By an igneous rock I mean, of course, one which has been in a 

 state of fusion through heat. This fusion, however, differs from 

 that which has been undergone by most rocks artificially produced, 

 such as slags, because it has always taken place in the presence of 

 water ; and further, the material has often solidified, and even crys- 

 tallized, not only without the expulsion of, at any rate, all the 

 water, but also under considerable pressure. Probably the nearest 

 approach to solidification under conditions similar to that of a slag 

 is given in the case of lavas, immense volumes of steam being 

 generally disengaged from the flows as they are emitted from a 

 volcano. I draw attention to this at the outset, because I think it 

 possible that it may prove to be a matter of primary importance in 

 certain of our investigations. 



"We ought, however, before proceeding further, to glance at two 

 objections which might be started ioi limine. 



(1) That no classification is possible, because nature has not 

 made distinctions ; she is too protean to be bound by our fetters. 



(2) That it is impossible to draw a hard and fast line between 

 igneous and sedimentary rocks, because the former are frequently 

 only the result of metamorphosis of the latter carried to an extreme 

 degree, so that the one series passes gradually into the other. 



As regards the former of these objections, we may remark that 

 on the assumption that igneous rocks have solidified from a state of 

 fusion (whether part of the original magma of the earth or stratified 

 rocks subsequently melted), we should anticipate difficulties in classi- 

 fication, and not expect to find very sharply defined lines of separa- 

 tion in either chemical or mineral composition. This difficulty, 

 however, is not confined to petrology ; the biologist, for instance, is 

 not deterred by the admitted difficulty of distinguishing a species 

 from a variety, or of deciding whether species have an independent 

 origin. Hence, for all practical purposes, species exist alike for the 

 most thorough-going evolutionist and the most confirmed believer in 

 special creations. Classification is a necessity if progress is to be 

 made ; distinction of things is needed for distinction of thought ; and 

 over this difficulty we need not linger, for we shall find that, prac- 

 tically, although intermediate forms may exist, the majority of rocks 

 can be grouped around certain types. 



The second objection may receive a like answer ; and I may add 

 further, that if we agree upon certain characteristics as denoting an 

 igneous rock, the antecedent history of the rock (for our special 

 purpose) becomes immaterial. For instance, I can think of a piece 

 of glass as an (artificial) igneous rock, even though I may have 

 formerly seen a crucible full of the material from which it has been 

 made. 



There are, moreover, as it appears to me, two rather considerable 



