EDITORIAL. 739 



not be denied that rock magmas at times are known to attain 

 extreme liquidity. Moreover, there must undoubtedly be a num- 

 ber of different physical causes at work conjointly, each of which 

 may preponderate under favorable conditions, so that it is quite 

 probable that no single process will be found adequate to explain 

 all the phenomena in question. 



It is interesting to observe that, while the majority of petrolo- 

 gists are engaged in studying the evidences of differentiation of 

 molten rock magmas, the theory of magmatic synthesis proposed 

 by Bunsen is not being wholly neglected. From the nature of a 

 portion of the evidence it is possible to frame diametrically 

 opposite hypotheses, but when all of the conditions are taken 

 into account it would seem that but one of the hypotheses can 

 have a general or far-reaching application. Prof. Sollas's paper, 

 " On the Origin of Intermediate Varieties of Igneous Rocks by 

 Intrusion and Admixture, as Observed at Barnavave/Carlingford," 

 demonstrated how intimately the material of an acid molten 

 magma may penetrate the interstices of a highly fractured rock, 

 in this case basic ; the delicate veins thinning to almost micro- 

 scopic dimensions. Instances of this kind are well known. The 

 assumption, however, that this process has taken place to a very 

 considerable extent, and has produced bodies of rock of inter- 

 mediate composition, seems to ignore the probable physical con- 

 ditions under which rock magmas are irrupted, and also the 

 geological probabilities of such things happening. Thus there 

 may be no defect in the logic of the assumption as an abstract 

 idea, but there may be little or no probability of its ever taking 

 place to a considerable extent in nature. 



Other petrological papers were presented by Prof. Sollas, Mr. 

 Watts, Dr. Johnston-Lavis, and an interesting account of the vol- 

 canic phenomena of Japan was given by Prof. Milne, and 

 illustrated by lantern slides. It cannot be out of place, for one 

 who has been fortunate enough to have been a guest of the 

 Association, to express a high appreciation of the honor, as well 

 as of the generous social hospitality which has become a distin- 

 guishing characteristic of these meetings. J. P. I. 



