218 The American Geologist. March, 18<j7 
volcanics are called andesites, on the orpound of their siiuilarity with 
the modern andesitic lavas. 
It might be pointed out that as these andesites are described as pos- 
sessing a grovindmass "originally very glassy" they deserve in con- 
sistency the pi-eflx apo as much as do the devitrifled rhyolites. This, 
however, is not the serious difficulty with the term andesite, that it 
does not indicate the alteration subsequent to consolidation. Are these 
volcanics of andesitic composition? The analysis of what was consid- 
ered the most basic type (p. 33) can scarcely be considered that of a 
normal andesite. The analysis is as follows: 
SiO.3 63.25 
TiOg Trace 
A1^03 : 14.89 
Fe^Oa • ^-^4 
FeO None 
MgO 0.82 
CaO 0.59 
K.,0 4.78 
NaoO 4.47 
P06- 0.61 
Hgd (by PbO) 2.67 
CO2 0.78 
Loss by ignition not accounted for by Hr,0 and COg 
and including small amounts of CI and F of apa- 
tite 0.53 
99.93 
The high alkali percentage and the exti-emely insignificant amount of 
lime present in the rock quite preclude the predominence of a basic 
feldspar. The lime is abnormally small even for an alkali feldspar rock. 
The amount of P.;,0- (0.61) present in the analysis, demands, to form ap- 
atite 0.72 parts of CaO. Allowing for a reasonable amount of error 
the lime still falls short of what is necessary for the apatite and for the 
calcite mentioned by the author and indicated by the percentage of CO2 
if the CO9 is all combined with CaO. 
It was from the presence of this calcite that the basic character of 
the feldspar was inferred, but presumably the ferromagnesian constitu- 
ents, which were described as normal hornblende or augite, contain 
lime, which might give rise to some of the calcite. Both this analysis 
and that of the aporhyolite (p. 51) indicate anorthoclase as the predom- 
inating feldspar. In the other types described as andesites the feld- 
spars are said to have the extinction angle of labradorite approaching 
andesine, of labradorite and of basic andes ne. In these cases the test 
of analysis has not been applied, but in the single case where an analy- 
sis was made the composition seems to be that of a trachytic rather 
than an andesitic lava. 
(3) The lavas with a porphyritic structure are termed iwrpliyriea, 
whether acid or basic. Thus porphyry becomes a term merely indica- 
