Prof. J. W. Judd—The Lavas of Krakatoa. 9 
Tf, as the consideration of these rocks at Krakatoa so strongly 
suggests, the minerals crystallized out of a magma, and the residuum 
of mixed silicates can be separated to a greater or less extent, and 
then recombined in fresh proportions, we have an explanation of the 
ejection from the same vent of materials differing most widely in 
their ultimate chemical composition, though presenting curious 
peculiarities in the enclosed minerals which are common to all of 
them. 
It is almost impossible to study the older and more recent ejections 
from Krakatoa without being driven to consider the possibility of 
the latter as having been to a great extent formed by the refusion of 
the former. Indeed the existence of knots of the unfused black 
glass in the midst of the modern pumices, and portions of the same 
material clinging to the crystals embedded in the recent obsidian, 
seem to render the fact of this refusion all but certain. How this 
refusion might have been brought about, a few very simple considera- 
tions will, I think, enable us to understand. 
The late Dr. Frederick Guthrie, whose early death was so great 
a loss to science, was engaged in a number of researches which have 
a very important bearing on questions of petrogeny, and are of 
great suggestiveness to the geologist. Solutions of various salts 
when cooled down are found to yield successive crops of crystals of 
ice or of the salt, until at last the remaining mixture of the two 
substances in a definite proportion are left behind, forming the 
bodies to which Dr. Guthrie gave the name of Cryohydrates. He 
subsequently showed that mixtures of metals or of salts behave in 
the same way when reduced to liquid condition by heat, and for 
those substances, compounds which separate out like the cryohydrates 
from a solution, he proposed the name of Eutectic bodies or Hutectics. 
The chief characteristics of these bodies is the lowness of their 
temperature of fusion. 
Dr. Guthrie himself clearly saw the importance of these considera- 
tions to the geologist. We are continually dealing with mixtures of 
salts (silicates) from which a number of definite crystallized bodies 
have separated out, till at last a residuum is left which consolidates 
at a lower temperature than any of them. The determination of the 
nature and composition of these eutectic silicates is a problem of the 
very greatest interest to petrologists. In a still later memoir, one of 
the last which he wrote, Dr. Guthrie attacks a closely related question 
which is of even greater interest and importance to the geologist. 
That water plays an important part in the liquefaction of the igneous 
masses of the Harth’s crust has been maintained by Scrope, Scheerer, 
Bischof, Daubrée, and many other observers, and cannot, indeed, be 
doubted by any one who has studied the phenomena attending the 
extrusion of lavas from a volcanic vent. But as to the exact réle 
played by the water in such molten masses, there has been much 
difference of opinion, and the researches of Guthrie are of the greatest 
importance, as throwing new light on this very interesting question. 
The influence of the presence of water in lowering the’ fusion 
