UPOLU. 315 
2. GEOLOGICAL STRUCTURE. 
Rocks, their Mineral Characters.—The following are the principal 
varieties of basalt found on the island: 
1. Dark grayish-blue and grayish-black basalt; very compact 
without cellules; fracture a little conchoidal; no distinct crystalliza- 
tion; no imbedded grains of chrysolite; lustre slightly glistening. 
Resembles the rock of Cockscomb Hill, Tutuila, page 310. 
2. Similar to the above, but a little cellular and containing minute 
particles of chrysolite. 
3. Grayish-blue; no lustre; rough fracture; harsh feel; some- 
times very compact, but generally cellular; occasionally contains 
chrysolite. 
4. Dark grayish-blue ; containing crystals of chrysolite and augite 
thickly disseminated ; both very compact and cellular. 
5. Black ferruginous basalt; very tough; fracture smooth, a little 
conchoidal ; lustre glistening; usually very cellular and containing a 
few disseminated grains of chrysolite. 
6. A grayish dark-blue basalt, porphyritic with very thin tabular 
feldspathic crystals. Another porphyritic variety, consisting of the 
same coloured base, speckled white with points of feldspar. 
7. Scoriaceous basaltic lava; brown, dark grayish-blue or brown- 
ish-red, very light and cellular, or consisting solely of the thin parietes 
of small spherical cellules. ‘The material of the rock is without lustre 
and resembles var. 3. 
These several kinds are quite common. All but the fifth and 
seventh occur in the central district of the island, and may be consi- 
dered as the older rocks of the island. The third and fifth are the 
usual forms presented by the more recent rocks. The seventh is 
found in and about the craters, as at Tafua. 
The porphyritic varieties (6), and the basalt with imbedded augite 
(4), are abundant along the rocky coast between Laulit and Solo-solo. 
The compact basalt (var. 1), is also found along the same coast. 
Particular localities of the other varieties need not be mentioned, as 
they are very generally distributed over the island. 
Besides the minerals already noticed, the rocks often contain mag- 
netic iron in small grains or crystals. At a few places along the 
shores magnetic iron sand may be collected by the handful. Five 
miles east of Apia is one of its localities, 
