H. 8. Washington — Rhyolites of Lipari. 461 



the Kilauea lavas by Day and Shepherd 19 are, so far as 

 I know, the only ones that convey any just idea of the 

 conditions of the various gases as they exist in the 

 magma. The possible interreactions between them, at 

 different temperatures and pressures and with different 

 mixtures, are numerous but have been little studied so 

 far. This is a topic into the consideration of which we 

 cannot enter here. 



It would seem, however, that although the specimens 

 of gas collected and analysed show a greater or less 

 degree of oxidation, as has been pointed out by Day and 

 Shepherd, yet there still remains in the residual gases 

 a notable percentage of oxidizable, and therefore re- 

 ducing, gases such as hydrogen, carbon monoxide, and 

 sulphur vapor. It might therefore be suggested that the 

 iron is in the ferrous condition because it has been kept 

 from oxidation by the general reducing effect of the 

 gases. Or one might argue in the other direction, so to 

 speak, and hold that the generally oxidized condition of 

 the gases is to be attributed (apart from possible atmos- 

 pheric influences), to reduction of original ferric iron. 

 Of the two the former seems to me to be the more 

 plausible because we have reason to believe that there 

 exists, beneath the uppermost "crust" of the earth, a 

 zone of material that is composed in great part of metallic 

 iron or an iron-nickel alloy, analogous to the siderolitic 

 meteorites. 



But, assuming either of these alternative hypotheses, 

 it remains to be explained how the ferrous oxide becomes 

 oxidized to ferric during crystallization, as appears to 

 be the case. For the present the matter must be left in 

 abeyance, and the data are presented here so as to call 

 the attention of penologists and geophysicists to a little- 

 known feature of the chemistry of igneous rocks that 

 may possibly lead to some generalization as to the char- 

 acter of magmatic gases and the true composition of the 

 sub-superficial magma. 



Refractive Indices of Rhyolite Glasses. 



Dr. Merwin kindly determined the refractive indices of 

 several of the Lipari glasses, as well as those of an obsid- 



19 Day and Shepherd, Bull. Geol. Soc. Amer., 24, 573, 1913; C. E. Acad. 

 Sci., 157, 1027, 1913. E. S. Shepherd, The Composition of the Gases of 

 Kilauea, Bull. Hawaiian Vole. Observatory, 7, No. 7, 1919. 



