102 LABRABOPaTE-NOEITE WITH [May I9O9, 



In his recently published work, ' The Data of Geochemistry ' 

 (U. S. Geol. Surv. Bull. No. 330, 1908, p. 249), Dr. F. W. Clarke 

 says on this point: — 



' The essentia] point in Vogt's work is tbat he attempts to apply modern 

 physico-chemical methods to the investigation of magmas, and whether bis 

 conclusions are maintained or not they are at least suggestive.' 



I think that by the present investigation of a given eruptive 

 rock, I have established that the processes of crystallization in a 

 magma may be legitimately explained in all their details according 

 to physico-chemical laws, and consequently that my conclusions 

 ' may be maintained.' 



The difficulties increase with the number of the components. 

 The natural method of research is, therefore, to begin with rocks 

 containing only one or two principal minerals, and subsequently to 

 study the rocks of more complex composition. 



Through physical chemistry the science of petrography has 

 acquired a new method of research, which will throw light upon 

 much that has previously been mysterious in our eyes. 



Discussion. 



Dr. Teall said that more than twenty years had elapsed since 

 he first recognized the great importance, so far as petrology was 

 concerned, of Prof. Guthrie's researches on cryohydrates and 

 eutectics. During that period great advances had taken place in 

 our knowledge of the laws of solutions, and the Author had done 

 more than any one else in applying these laws to the phenomena 

 of igneous rocks. He (the speaker) had no doubt that the present 

 paper would prove to be an important communication on the 

 subject. 



Dr. Flett said that he welcomed this paper as an important 

 contribution to the theory of the crystallization of basic rocks 

 according to physico-chemical laws. The case discussed by the 

 Author, though not exactly similar to any British rock with which 

 the speaker was acquainted, might still be regarded as one of a 

 group of which there were many British representatives. The 

 rapid progress which the study of rocks was making along these 

 lines was most gratifying, and was of cardinal importance to 

 theoretical petrology. 



Mr. Barroay drew attention to some minor points, as to which 

 there was room for difference of opinion. Some authorities would 

 call in question the view that the large felspars separated out from 

 the ' fusion-solution ' before the iron-ores : the alternative view 

 being that during growth the large crystals forced the already 

 formed grains of iron-ore outwards, so that eventually they formed 

 a thin fringe round the felspars. The larger crystals of the latter 

 were often supposed to have separated out from the magma 

 at' a great depth and under a great pressure ; and, further, this 



