1921.] 
Thomson.—The Geology of Western Samoa. 
55 
at the north end and round the top of the talus slopes at the south end. 
The sulphur-crystals are of the unstable monoclinic variety. 
The lava-field from the base of the crater to the sea has an average slope 
estimated by Anderson at about 6°. The lava is mostly of the typical 
pahoehoe type, smooth over a wide area, though very irregular in detail, 
with typical small cracked domes with corrugated and ropy surfaces. Near 
the crater areas of rough broken lava simulating aa are not uncommon, but 
they are made of broken pahoehoe, and I saw no typical aa. Anderson’s 
explanations of the origin, of the aa type of lava are diametrically opposed 
to those of Jaggar, and the reason lies probably in the fact that he mistook 
areas of broken pahoehoe for aa. For a more detailed description of the 
lava-surface the descriptions of Jensen and Anderson should be consulted. 
Further exploration of the tunnels, which are now accessible by numerous 
downbreaks, is desirable. In particular, the soluble salts should be collected 
and analysed before they are all washed away. 
It is worthy of note that the growth of vegetation on the lavas of 1905 
and 1906 greatly exceeds that on the 1894 or even the 1860 flows of 
Kilauea, presumably because of the moister climate. I noted three species 
of fern, two shrubs, an orchid, and a grass just below the crater, and much 
moss near the crater. A botanical investigation in the near future is 
very desirable. It is difficult to reconcile the amount of growth on the 
Matavanu lavas with the lack of bush on the 150-year-old lava-fields of 
Aopo. 
The lavas of Matavanu have been examined microscopically by Jensen 
and Weber, but no analyses have been made. They are olivine-rich 
feldspar basalts with titaniferous augite, and generally with a considerable 
proportion of glass. The chilled surfaces of the pahoehoe flows are typical 
tachylites. Jensen states that the Matavanu lavas are richer in iron- 
ores than any of the earlier flows. 
The Prehistoric Volcanoes. 
Savaii. 
Except by Friedlander, little has been written of the geology of Savaii, 
outside the historic volcanoes, and little exploration either of the coast 
or of the interior has been made. The island has an elongate dome shape, 
and seen from the steamer passing it on the south reminded me greatly 
of Mauna Loa in Hawaii in outline and slopes. Like Mauna Loa, it has 
a series of parasitic cones along the crest on both eastern and western 
sides, and is highest at the centre. A study of the map suggests that, 
like Mauna Loa, Savaii is dominated by a longitudinal fissure, which is 
continued to the east-south-east by Apolima, Manono, and Upolu. On 
this line from west to east lie the craters of Mauga Loa, Mauga Afi, Siope, 
Te’elagi, Matane, and many smaller unnamed ones. Friedlander states 
that this range is called Tuasivi (backbone) by the natives. A series of 
craters at the eastern end from Mataolano to Cape Tuasivi suggests a 
slightly diverging fissure directed a little to the east of south. From the 
central mass a third fissure probably runs north through Pule and Matavanu 
to the coast near Safune, there being in the latter neighbourhood an 
elevated area to the east and a depressed area to the west with a cliff 
which seen from Matavanu suggested a fault-scarp. Friedlander, who 
also recognizes the above structural lines, extends the latter to Taga on 
the south coast, and mentions also that there are smaller north-south 
