Vol. 57.] ANNIYERSAEY ADDRESS OF THE PRESIDENT. 



IXXT 



Some years ago I directed attention to the possible application of 

 GuthiTie's work on cryohjdrates and eutectics to petrographical 

 questions, and the experience since gained has tended rather to con- 

 firm me in the views which I then expressed. Fused salts which do 

 not act chemically upon each other show, when mixed in eutectic 

 proportions, a marked tendency to form spherulitic, and what may 

 be called micropegmatitic, iutergrowths. It has since been proved 

 that the same is true of alloys. Thanks to the kindness of Mr. J. E. 

 Stead, I am able to give two figures, drawn from photographs, 

 which illustrate this fact, and side by side with these are placed 

 figures of micropegmatitic and spherulitic structures copied from 

 Prof- Iddings's memoir on the rocks of Obsidian Cliff. 



'i^B^^ 



'^>^' 



mn 



rc^^ 



FMifi'r^'"- 



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Figs. 1 & 3 = Spheruhtic and micropegmatitic structures in obsidian. (After 



Iddings, yilth Ann. Eep. U. S. Geol. Surv. 1885-86, pi. xv.) 

 Figs. 2 & 4 = Similar structures in eutectic alloys : from microphotographs by 



Stead. 2 = A simple spherulite in the eutectic of lead and antimony ^ ; 



4 = Micropegmatitic structure in magnolia-metal (lead, 80 per cent. ; 



antimony, 15 per cent. ; and tin, 5 per cent.). 



The outlines of this spheruhte are somewhat, too sharply drawn. 



