TUTUILA. slit 
lava. This is the only instance, as far as I could learn, of the exist- 
ence of any recent volcanic appearances. 
The basaltic conglomerate consists of fragments of the basaltic 
rocks: its general characters may be inferred from our description of 
the similar beds at Tahiti. The fragments, where I examined the 
rock, were partially rounded, and some of them more scoriaceous than 
any of the basalt observed in place on the island. It had a dark 
colour, and a dull earthy aspect when broken. It occurs in layers 
near the western entrance of Pango-pango Harbour, and along the 
shores in that direction where it appeared to underlie the basalt. 
Numerous other localities of it probably exist, but in our rapid 
glance at the island, I did not meet with them. 
The basalt generally exhibits a tendency to a columnar structure, 
but no distinct columns with regular polygonal forms were observed. 
A short distance to the east of the harbour there stands a small round 
islet, rising from the waves lke the venerable ruins of an ancient 
tower. Its erect sides consist of rude columns of basalt. <A few 
spots of verdure relieve the blackness of the walls, and the broken 
summit is overgrown with shrubbery and a few large trees. ‘The bold 
shores and steep rocky escarpments, which are the prominent fea- 
tures of Tutuila, result, in many instances, from imperfect vertical 
cleavages, or a tendency to a columnar structure, characterizing the 
basalt. 
Tutuila has undergone so great changes by convulsions and de- 
nuding agents, that the outline of the volcanic cone or cones from 
which the rocks of the island were ejected, is wholly obliterated. 
With our present imperfect information, we do not attempt to trace 
out the position of the central vent or vents ; we can only compare the 
island, in general features, to Kauai, among the Sandwich Islands, 
and Tahiti, of the Society Group. The basaltic lava, on the south- 
west side, according to Mr. Cunningham, did not flow from a 
crater, but probably from some fissure or opening which is now con- 
cealed. 
The harbour of Pango-pango, with its mural enclosures, reminds us 
of such valleys as the Val del Bove of Etna, and unless we may look 
to convulsions and subsidences as the sources of its formation, or to 
such phenomena as appear at Kilauea, we are at a loss to account for 
its extent and features. 
