GENERAL GEOLOGY 
4 1 
ferrecl to the Carboniferous. It may have been derived 
from just such a series of rocks as the Vancouver Series, 
and it is associated with the same granitoid eruptives which 
accompany the Vancouver Series along the Alaska coast. 
IGNEOUS ROCKS 
(n) Hornblende-biotite-tonalite (372), identical with a boulder 
from Plover Bay described below. 
Hornblende-biotite-tonalite (205), nearly identical with the above 
but showing many perfect amber-colored titanites just visible to the 
eye. This is represented in the collection by several varieties. 
(0) Normal, rather coarse grained, biotite-hornblende-granite with 
abundant porphyritic Carlsbad twins of orthoclase. 
(p) Dark grey medium-grained granite , with much more biotite 
than the other forms. 
(y) Aplite . A very compact, almost aphanitic, pearl grey pebble ; 
agrees almost exactly with the aplite from St. Matthew Island. 
( r ) Porphyritic liparite perlite ( 218 ). White feldspar crystals 
appear abundantly in a brick-red base of pitchstone. 
The microscope (plate iv) shows a blood-red glass, affected every¬ 
where by a perfect perlitic structure. The glass shades into deep red- 
brown spots or into pale red areas. The perlitic centers are often 
occupied by oil-green amorphous-appearing areas of microfelsite, which 
polarize fibrous and negative. This is also developed into minute 
spherulites, which are partly enclosed in the feldspar, and are broken 
and moved apart. The original fissures are now represented by broad 
bands which are colorless and granularly devitrified. The biotite is 
twisted and largely decomposed by fusion, with separation of black ore. 
The feldspars are often broken. The rock is an oligoclase-albite-bear- 
ing perlite. It represents the first step—the embryonic form —in the 
development of lithophysae, in accord with the explanation of the proc¬ 
ess given by Professor Iddings. The separation of water at these 
points has caused the development of compounds having a green color, 
as is common in lithophysae, and has caused disturbances there — the 
cracking of the spherulites, and polarization, while the glass around is 
unstrained and unaltered. 
(s) Augite-orthophyr (207 ). A chocolate, felsitic base, with small 
flesh-colored feldspars and red biotite. The feldspars and the green 
augites are wholly decomposed under the microscope. 
