272 HENRY S. WASHINGTON 
Von Lasaulx’ concludes that the rock-magma of the augite 
andesites of Hemmerich in the Siebengebirge must have been 
much more rich in hornblende at an early stage, and that the 
preponderance of augite, as well as magnetite, could have come 
about through resorption (Einschmelzung) of the hornblende. 
Grosser,? in a later work on the same region, comes to the same 
conclusion. 
Hatch3 notes a connection between the alteration of the horn- 
blende and the presence of magnetite in the groundmass of certain 
Peruvian andesites, observing that in cases where the hornblende 
is “resorbed” magnetite is abundant, while in rocks where the 
mineral is unchanged the groundmass contains no magnetite 
grains. No definite mention of augite is made in this connec- 
_tion, but on page 359 he states that ‘hand in hand with the 
resorption of the hornblende goes an increase in pyroxene and 
magnetite.” 
Finally two examples drawn from my own experience may 
be given, one the hornblende basalts of Kula in Asia Minor,‘ and 
the other the andesites of A‘gina and Methana.5 In these 
the relation of the abundance of augite and magnetite grains in 
the groundmass to the alteration of the hornblende is well shown. 
We see from these examples that in many andesites, as 
well as in other volcanic rocks, a part of the groundmass augites 
(and magnetites) have been derived from hornblende or biotite 
through alteration, whether ‘‘magmatic” or ‘‘molecular’’ it 
matters not. 
It is possible that we have in this fact the explanation of the 
so frequent occurrence of imperfect grains of augite in the 
groundmass of many rocks. Augite and magnetite tend to be 
anomalous in this respect, as the groundmass crystals of the 
other rock-forming minerals —the feldspars, quartz, hornblende, 
Von LASAULX, Sitz. ber. Niederrh. Ges. in Bonn., XLI., 155, 1884. 
2GROSSER, Min. Pet. Mitth., XIII., 77, 1892. 
3HatcH, Min. Pet. Mitth., VII., 347, 1886. 
4Am. J. Sci. LX VII, 121, 1894. 
5 Jour. OF GEOL., III, 21-46, 1895. 
