1921.] Thomson.—The Geology of Western Samoa. 57 
Evidently at first ashes and slags were ejected, and later lava poured out 
at one side. Each new eruption found a fresh outlet and built a new 
cone. This agrees closely with the conditions found on Mauna Loa in 
Hawaii. , 
Farther to the east the heights decrease slowly, the river-courses become 
wider and deeper, and the quantity of water increases considerably. The 
numerous small cones are so low as hardly to be seen in the bush until one 
is at their foot. An exception is Toiavea, 1,066 m. (3,493 ft.), which rises 
200 m. (656 ft.) on the west and 300 m. (984 ft.) on the east above its base, 
and consists of a steep cone of slag and lava, with an angle of 40°. The 
walls of the crater on the east and west sides are somewhat crumbled, so 
that the hill, seen from the north-west or the south-east, appears to have 
two summits. It is a well-known landmark to the Samoan sailor. In the 
lava on its western slopes there are several deep, gaping fissures and two 
lava-tunnels. 
About 2 km. south from Toiavea is a small well-preserved crater, 
occupied by a round lake, Mataulanu. The crater-walls rise about 40 m. 
(130ft.) above the level of the lake and a little more above the surrounding 
country. They consist of well-weathered ashes and slags, which are on 
that account impermeable. Lake Mataulanu is accessible by track from 
the inland village of Tapueleele, in the Fa’asalele’aga district. Other 
conspicuous cones in this neighbourhood are Matofa and Olomanu. 
Among the cones to the south of Toiavea the most noteworthy is 
Mafana, which rises from a base of 600 m. (1,968 ft.) to a height of 971 m. 
(3,186 ft.). The crater is about 80 m. (262 ft.) to 90 m. (295 ft.) below 
the rim, and its bottom is round, very flat and rather swampy, and has 
a diameter of about 350 m. (382 yards). From it block lava (aa) flowed 
out to the east. The mountain itself is densely wooded. 
On the south coast there are large very fresh-looking lava-fields near 
Taga and between Nu’u and Tufu, which appear to have come from small 
cones in this neighbourhood. Some old Samoan songs are said to refer 
to these eruptions. 
The Peninsula of Tafua, on the south-east corner of Savaii, bears a 
small group of volcanoes of about 200 m. (656 ft.) in height, some of 
which have well-preserved craters, and one particularly well so. Its outer 
slopes are made of well-stratified submarine tuff, which has evidentlv been 
elevated, but the inner, almost vertical, walls of the crater consist of thin 
stratified lavas of a thickness of only 10 cm. to 30 cm. At the bottom, 
which is only a few feet above sea-level, there is the entrance of a lava- 
tunnel. On the north-eastern side of the peninsula there is a lava-field, 
densely wooded, but still too recent to be cultivated. 
On the northern side of the Tuasivi lie the historic fields already 
mentioned, and south-east of the Matavanu field is the relativelv new 
lava-field of Lealatele. It bears timber of considerable size, but there 
is very little soil, and the ropy surface of the lava is still well preserved. 
A few specimens of the prehistoric lavas of Savaii have been petro- 
graphically examined by Jensen and Weber.* All the rocks belong to the 
basalts, except two described by Weber. One, from the Sili stream, is a 
phonolite with well-marked phenocrysts of sanidine in a fine-grained green 
base consisting of sanidine laths with prisms of aegirino, hauyne, and a 
* Weber mentions also descriptions by Mohle, Kaiser, and Klautsch, but I have not 
been able to consult their papers. 
