450 H. S. Washington — Rhyolites of Lipari. 



Little need be said here of these analyses ; they are 

 qnite typical of many rhyolites, and many very similar 

 ones may be found in the same subrang (liparose, 1.4.1.3) 

 in the collection of analyses given in Professional Paper 

 No. 99, of the U. S. Geological Survey. The pumice shows 

 considerably less silica, which is compensated for by the 

 higher water. As the pumice belongs to an earlier series 

 of eruptions, while the . obsidians represent the last 

 phase of eruptions, the idea naturally suggests itself that 

 much of the contained water was lost from the magma 

 before the last eruptions. 



The most interesting feature in all the first three 

 analyses is that, while the total amounts of the iron 

 oxides are about the same, the amount of FeO is largely 

 in excess of that of Fe 2 3 . This seems to be character- 

 istic of the glassy forms of the same magma, as con- 



9Uin^^S^J0O{OI{ Ql\l UT UOTXBJ9I 9SJ9AUT 9I[; t[lTAV p9^SHJ^ 



forms, and will be discussed later. 



There are scarcely more than traces of magnesia, a 

 small amount of lime, and but little titanium. The 

 presence of zirconia in quite distinct amounts is of inter- 

 est ; while manganese and phosphorus are almost wholly 

 absent, as is baryta. The presence of very decided 

 amounts of both sulphur trioxide and chlorine is note- 

 worthy. It may be mentioned that, in the determination 

 of water by Penfield's method, in both obsidians and the 

 pumice, a distinct ring of sublimate was formed in the 

 glass tube. This ring gave distinct reactions for chlorine 

 and sulphur trioxide, in all three cases. 



Classification.— The norms of the first three specimens 

 analysed are as follows : 



12 3 



Quartz 28.68 



Orthoclase 29.47 



Albite 35.11 



Anorthite 2.22 



Diopside 0.99 



Hypersthene 1.95 



Magnetite ......... 0.70 



Ilmenite . 0.15 



These place all three in liparose, the Rocche Rosse 

 obsidian having the symbol 1.4.1.3 ; that of Forgia 

 Vecchia I. "4.1.3. ; and the Monte Pelato pumice 1.4.1.3. 



29.58 



26.64 



28.36 



30.58 



34.58 



35.11 



1.67 



0.56 



1.70 



none 



1.26 



1.88 



0.93 



0.70 



0.15 



0.15 



