UPOLU. 323 
The twisted scoriaceous lavas are best displayed on the south side 
of the island, across from Apia, in the vicinity of Simapu. They have 
been described to me by my associates, who took that route for 
their investigations, as resembling the products of the most modern 
eruptions. 
Lava caverns and long subterranean passages abound on this part 
of the island (the western district), especially on the south side. 
They are like those so often described as occurring about recent vol- 
canoes, to which we have alluded in our account of the Sandwich 
Islands. Some of them open just at the water’s surface; others a 
little below it, and it is then necessary to dive, to reach the entrance, 
and swim some distance before finding a landing-place within the 
cavern. The whole country is so thoroughly penetrated by caverns 
that hollow sounds are often heard beneath the footsteps of one tra- 
versing the region. 
One of these caverns was visited by Mr. T. R. Peale, who has 
given me the following facts regarding it. ‘This cavern is near 
Salani on the south side of the island, eight or nine miles from its 
western extremity. It was entered about a mile and a half from the 
sea by a perpendicular descent of twenty-five feet, through an open- 
ing made apparently by the falling of the roof. The rock overlying 
the cavern was about fifteen feet thick. 
This subterranean passage proved to be a regular arched way, 
fifteen feet wide and eight high, extending down towards the sea, in 
a southeasterly direction. It was followed for nine hundred and eight 
feet, when the water within reached the roof above, and prevented 
farther exploration. The top was generally smooth, but was peeling 
off in many places in lamine from one to ten inches thick. The flat 
roof was marked longitudinally with furrows, evidently formed when 
the rock was flowing lava; they were so regular, and continued for 
such a distance, that they might be compared to the track of a rail- 
way. ‘The rock is the glistening ferruginous lava (variety 5) already 
described. 
The roof, sides, and bottom were covered in many places with a 
white or yellowish-white incrustation, in the form of stalactites or 
stalagmites, deposited by the percolating waters. ‘The stalactites are 
short cones; the largest of them are two inches long, with a base of 
an inch. ‘The stalagmites have a flattened hemispherical shape, 
about three inches wide, with a smooth surface and an imbricated 
appearance along the sides. ‘These masses are composed of a series 
