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PACIFIC SCIENCE, VoL XX, July 1966 
as well as the shelf area between the isthmus 
and the island of Kahoolawe, is devoid of any 
anomalies, suggesting that this area is clear of 
any intrusives. A negative embayment of 30-70 
gammas in the contours north of the West 
Haleakala Volcanic Vent anomaly suggests that 
a shallow north-striking zone of dikes is present 
within the lavas of the Haleakala dome. At its 
southern end, the zone of dikes, as suggested by 
the magnetic anomalies, is offset westward by 
a distance of six miles from the geologically 
defined North Rift Zone of Stearns and Mac- 
donald (Fig. 20). This offset is so great that 
it is highly unlikely that the two are related. 
QUANTITATIVE ANALYSIS OF THE MAUI AND 
KAHOOLAWE MAGNETIC ANOMALIES: As On 
Hawaii, selected magnetic profiles were cor- 
rected for the magnetic effects of topography 
before quantitative analysis was attempted. 
Using analysis techniques, as described earlier, 
depth and size estimates, and magnetization 
contrasts were derived for the anomalies of 
Maui. These values are listed in Table 3. 
All the magnetic anomalies, with the notable 
exception of the West Haleakala Volcanic Vent 
anomaly, are reflected also by gravity highs 
(Kinoshita and Okamura, 1965) which suggest 
that, as on the island of Hawaii, the magnetic 
anomalies are due to dense, highly magnetic, 
intrusive rocks located within the volcanic 
vents. The West Haleakala Volcanic Vent, as 
defined by a single dipole anomaly, appears to 
be of shallow origin and only 2 km thick, 
though broad in horizontal cross section. 
As on the island of Hawaii, the anomalous 
geologic bodies giving rise to the magnetic 
anomalies all appear to be vertically oriented. 
The apparent reversals in the direction of 
magnetization observed for the two West Maui 
magnetic anomalies could be due to reversely 
polarized rocks occupying the vents or to weakly 
magnetized rocks occupying the vents. It may be 
significant that weakly magnetized rocks were 
collected from intrusive rocks of the Wailuku 
series. The surrounding basalts of the same 
series recorded higher remanence effects of 
9 X 10 -3 cgs units. 
Island of Molokai 
geology: The geology of this island has 
been described by Stearns and Macdonald 
(1947). The island was formed by eruptions 
from two principal volcanoes, West Molokai 
and East Molokai. West Molokai now stands 
1,300 ft and East Molokai 4,900 ft above sea 
level. Both volcanoes were built up from the 
sea floor, probably during Tertiary time. 
East Molokai is built of basaltic lavas with a 
thin cap of mugearites. Dikes cut the lower 
members of the volcano and trend east and 
northwest. On the basis of the dips of the flows 
the main volcanic center lies north of the pres- 
ent coastline. Intrusive rocks are common, and 
consist of stocks, plugs, and dikes which occur 
Fig. 24. Sketch of the primary rift zones and volcanic pipe zones of the island of Molokai. 
