230 Hague and Iddings— Volcanoes of 
carries considerable lime, of which very little is taken up by 
the pyroxene, it is reasonable to suppose that all the larger 
feldspars are labradorite mingled with others which may be 
‘andesine and oligoclase. An analysis of the glass which 
forms the base of the pumice is given under number V. It is 
highly siliceous, showing a falling off in alumina, the feldspar- 
making element which together with the lime had not entered 
‘into the first crystallizing mineral, hypersthene. On the other 
hand the analysis shows a considerable relative increase of 
alkalies with the greater part of the potassa of the original 
rock, which had not been taken up by the minerals which 
crystallized out concentrated here in the residual glass. 
TABLE IT. 
Pumice. Hypersthene. Feldspar. Feldspar. Glass base. 
I TI. Iv. : 
Sid, . 62°00 50°33 56°41 56°95 69°94 
Al,Os 17°84 97 27°39 BT47 15°63 
FeO 22°00 0°69 trace 1°89 
CaO 5°37 1°88 9°87 9°10 2°49 
MgO 2°64 23°29 0-09 0°02 0°28 
K.,0 1°47 so ibes 0°36 0-48 2°85 
Na.O 4°29 pete 5:43 5°78 3°83 
MnO trace 0°64 Sa z pipe rae 
TiOz, O17 ai eared eats ie ae pied cea 
P20; 0°29 eal ite SU aNecus eae apa 
Ignition 1°66 oa ney ninlare 3°25 
100°13 99°11 100°24 99-80 100°16 
Specific gravity of III = 2°66 to 2°68. IV = 2°64 to 2°66. V = 2°29 
specimens brownish-green, which in places has a small black 
rder. This type of rock then is composed of plagioclase feld- 
spar, hornblende, hypersthene, a little augite and magnetite, that 
are found in porphyritic crystals embedded in a groundmass 
of the same, generally with the exception of hornblende, with 
or without glass. The feldspars appear to be less basic than 
those in the hypersthene andesite, giving extinction angles corre- 
_ sponding to andesine. The second variety of hornblende ande- 
site, which is represented only by hand specimens from Straw~ 
