AyXIVERSAP.r ADDRESS OF THE PRESIDENT. Ijg 



frequent occurrence. These are usually more acid than the rock 

 which they traverse, and they sometimes exhibit a well-defined 

 granophyric structure. There can hardly be any doubt that they 

 represent the still fluid and somewhat acid parts of the mass, which, 

 owing to internal movements were injected into portions that had 

 already consolidated. But there is still another kind of vein to 

 be found in some of the larger basic intrusive masses, where there 

 has been a segregation of the constituent minerals along certain 

 indefinite bands or lines, sometimes wavy or puckered. Pyroxene 

 and magnetite, for example, may be found aggregated into layers or 

 lumps which merge insensibly into the substance of the surrounding 

 rock. In such instances there does not appear to have been any 

 intrusion of one part of the mass into another, but rather a separa- 

 tion of some of the basic minerals along more or less well-defined 

 planes, or round particular centres. 



Both these structures in our eruptive rocks appear to me to be 

 deserving of much more careful investigation than they have yet 

 received/ An exhaustive stud}' of them could hardly fail to throw 

 light upon the changes which take place within the volcanic magma 

 by the separation of its constituent minerals. On the other hand, 

 it would bear closely on the origin of structures in the more 

 ancient gneisses, which appear rather to belong to some segrega- 

 tion or rearrangement in an original igneous mass than to any 

 subsequent mechanical or other metamorphism. 



It only remains for me now in conclusion to express again my 

 thanks to you for the honour which you conferred upon me two 

 years ago by electing me to be President of this distinguished Society, 

 and for the uniform kindliness and helpfnlness which have been 

 shown to me on every hand during my tenure of office. In vacating 

 the Chair I am happy to think that in my successor you welcome a 

 man who to the lustre of his scientific reputation adds this further 

 and valuable qualification, that he has already served you for many 

 years as Secretary, and is thus intimately acquainted with the 

 conduct of your affairs. 



^ The recent elaborate investigations of J. H. L. Vogt on the iron-ore deposits 

 of Scandinavia may be referred to in this connexion: Geol. Foren. Stockhohn, 

 Forbandl. vol. xiii. (1891) p. 476, and Mr. Teall's review, Geol. Mag. for 1892, 

 p. 82. 



