1921.] 
Thomson.—The Geology of Western Samoa. 
59 
only occasional outcrops of very vesicular basalt. The rock nearer the 
summit is more massive, but is fairly decomposed. There appear to be 
no valleys, and the few springs found are brackish. No petrographical 
examination of the rocks has been made. 
Upolu. 
Like Savaii, the Island of Upolu, from the disposition of its craters and 
summits, appears to be dominated by a longitudinal fissure from a little 
north of east to a little south of west. Very little information as to its 
geology has been put upon record, and Friedlander does not appear to 
have traversed the interior, nor can I add much information except as 
to the coasts 
Friedlander practically limits his observations, so far as the volcanic 
rocks are concerned, to the statements that in the western part there are 
a series of eruption-cones, more or less well preserved, and the lava on 
the coast sometimes looks as if it were recently formed, while that in the 
bush sometimes reveals itself as cake lava (pahoehoe) or block lava (act), 
and lava-tunnels are well preserved east of Luimu, but the greater age 
of the volcanic formations as a whole is shown by the greater erosion 
and the abundance of water. The originally porous lava has become 
impermeable to water owing to decomposition, and only round boulders, 
peeling at the surface like the skin of an onion, remain in a lateritic or 
clayey ground. The greater development of coral reefs, which become 
interrupted by being overflowed by lava as at Matavanu, also shows the 
greater age of the Upolu volcanics. 
The western end of Upolu is dominated by Tofua, a well-shaped volcano 
669 m. (2,195 ft.) in height, and containing, so I was informed, a crater. 
On its slopes there are a number of smaller cones. At its north-eastern 
foot lies the coconut plantation of Le uio sao va, near Mulifanua. Here 
the rock, a fairly weathered vesicular basalt, similar to that of Manono, 
opposite, lies everywhere near the surface. The ground is very gently 
undulating, and might well have been formed by an extensive pcthoehoe 
flow. Ofalau Hill is composed of a lighter-coloured, finer-grained, and less- 
vesicular rock. 
Along the south coast of Upolu the barrier reef fails except across a 
few harbours, and what reef there is is fringing. There are several steep 
promontories of volcanic rocks, which render travel along the shore from 
bay to bay very arduous. The bays have generally low, flat shores of coral 
sand or, in the case of Salani, basalt gravel, and the hills in the background 
are well eroded. Such rock as was seen in situ in the bays appeared to 
be basalt. 
The Aliepata district, at the east end of Upolu, is also mainly a coral- 
sand district, with lava showing here and there. There are several out¬ 
lying islets, one of which at least, Namua, is composed of a well-bedded 
tuff, possibly submarine, since it contains remains of corals. 
The north-eastern coast is marked by several deep harbours, with rCefs 
not barring the entrance, but following round the sides of the harbours a 
short distance from the land, and furnishing boat-harbours. Uafata Bay 
is steep-walled, and has a strong creek, which has brought down to the 
beach a great variety of rocks, mostly or all of basaltic types. Fangaloa 
Bay is also enclosed by steep walls, upwards of 1,000 ft. high, the watershed 
appearing nowhere to be more than three-quarters of a mile from the 
shores. There are several beautiful high waterfalls, which in spite of the 
