418 
PACIFIC EXPLORATION: J. P. IDDINGS 
by erosion, and consists of a central mountain about 2500 feet in height, 
with a vertical escarpment of fully a thousand feet which exposes 
horizontal basaltic lavas. The marginal ridges surrounding two deep 
bays are the remnants of volcanic slopes in which the lava sheets dip 
outward toward the surrounding lagoon. 
The still smaller island of Maupiti is the remains of a basaltic volcano 
almost completely submerged in the ocean. The encircling lagoon is 
relatively larger than those about the less submerged islands farther 
east. In fact there is a progressive relation between the width and 
depth of the lagoons around these islands and the apparent submerg- 
ence of the volcanoes. The most deeply submerged islands and rela- 
tively largest lagoons are in the west or northwest, that is, in the Lee- 
ward islands, and in the northwestern part of these. 
There is less submergence and the lagoons are less well developed 
at Moorea and Tahiti. However, in this, the Georgian group, Tetiaroa, 
26 miles north of Tahiti, is only an atoll, while Mehetia, 60 miles east 
of Taiarapu is said to be an extinct crater 435 meters high, having a 
peak to the north and a gentle slope to the south, and having a difficult 
coast. 
The islands of the Marquesan group, 600 miles northeast of Tahiti, 
are extinct and eroded volcanoes consisting of heavy basalts similar 
to those of Tahiti and the Leeward Islands, with quite subordinate 
amounts of trachytic lavas. Erosion has cut deeply into the volcanic 
mountains in places and has carved steeply walled valleys, surrounded 
by precipitous mountain ridges, with some commanding peaks, as at 
Traitors Bay and the Bay of Hanaiapa on Hiva-oa, and along the south 
coast of Nukahiva. This coast is very rugged with cliffs 1000 feet high, 
topped by hanging valleys. 
The coasts of Nukahiva and of Hiva-oa plunge steeply into the 
sea which in places is a thousand feet deep within a few hundred feet 
from shore. No coral reefs surround these islands, though a few frag- 
ments of corals are found on the beaches which occur at intervals along 
the coast. Small reefs of coral are said to occur in some localities in 
this region. The northwestern side of Nukahiva is a long, gentle vol- 
canic slope reaching sea level. 
In the Marquesan Islands, so far as my observations go, sea erosion 
appears to have progressed more rapidly than stream erosion in places 
where sea cHffs rise to great heights, with hanging valleys and with water- 
falls plunging into the sea. However, there are great differences in 
the topographic relief in neighboring parts of the same island, as on 
Hiva-oa, where in the western portion deep valleys have been cut with 
