370 
PACIFIC SCIENCE, Vol. XIX, July 1965 
tholeiitic and that the feeder pipe contains ul- 
trabasic rock. 
THE SOCIETY ISLANDS 
The Society Islands trend in a N 60° W direc- 
tion and are located between 148° and 152° W 
and 16° and 18° S. During August 1964, the 
writer, using a Worden gravimeter No. 366, 
made 137 gravimeter observations on the islands 
of Tahiti and Moorea. All gravity data are re- 
ferred to the absolute value of 978.9562 gal 
established for the Hawaii Institute of Geo- 
physics gravity base in Honolulu, Hawaii 
( W oollard, unpublished ) . 
Tahiti 
Tahiti can be geomorphologically compared 
with the island of Maui: each is a large, high 
land mass, connected with a small, lower one 
by a narrow isthmus. Tahiti-Nui is roughly 
elliptical in shape, measuring 23 by 18 miles, 
and is connected by the isthmus of Taravao to 
the Taiarapu Peninsula which is positioned to 
the southeast of Tahiti-Nui and measures 14 by 
9 miles. The highest point on Tahiti is 7339 
ft and is located near the geometric center 
of the island. The highest point on the Taiarapu 
Peninsula is 4341 ft, and it is located near the 
geometric center of the peninsula. The moun- 
