314 
PACIFIC SCIENCE, Vol. IX, July, 1955 
The groups of small lava shields here de- 
scribed may well have been supplied with 
lava from such dikes. The dikes are, of course, 
transverse to the supposed rift that supplied 
most of the lavas for the Wahiawa Plateau. 
The lava shields are too low to be shown by 
the 100-foot contour interval of the 1938 
edition of the U. S. Geological Survey’s topo- 
graphic map of Oahu. It happens that the 
40-foot interval of the 1917 U.S.G.S. map 
does have closed contour lines around four 
of the lava shields. The maps of Figures 14 
and 16 were prepared from the photolitho- 
graphic preliminary sheets for the 1938 edi- 
tion. These preliminary maps are on the scale 
of 1:20,000, and have two contour intervals, 
50 feet in the more rugged areas and only 10 
feet in the smoother areas, which brings out 
the lava shields very clearly. 
UNCONFORMITIES 
In sedimentary rocks one often finds un- 
conformities or marked differences between 
Fig. 16. Map of lateral lava shields between Kipapa 
and Waikakalaua Gulches. Contour intervals of 10 and 
50 feet. 
lots of strata deposited at different times. One 
lot may have a different attitude or inclination 
from the other, or they may differ in kinds of 
fossils, or kinds of rock, or the older may 
have weathered at its top to soil. Fossils can- 
not help in separating two lots of lavas made 
at different times, nor can differences in rock 
types often help in Hawaii where the rock 
Fig. 17. The lateral lava shield east of the depression 
in Figure 16. 
types are in general very similar. In a few 
places in Hawaii, however, older and younger 
lots of lava flows are separated by angular 
unconformities, where the older flows were 
truncated or bevelled and the newer flows 
mantled the eroded or faulted surfaces of the 
older flows. No such unconformities are 
known within the Koolau Range proper, 
although the Honolulu Volcanic Series lies 
unconformably on Koolau lavas in most 
places. 
Some unconformities may have the older 
and younger lots of strata or lava flows in 
essentially parallel position, but with a deeply 
weathered zone at the top of the older series 
that implies a considerable time interval be- 
tween the making of the older and the young- 
er lots of rock. A possible example of such 
an unconformity has recently been exposed 
in a road cut on the north side of Kameha- 
meha Highway about 0.7 miles west of Pearl 
City Junction (Fig. 18). This is not a con- 
clusive example for it may be merely a lesser 
unconformity within one of the larger bodies 
of lavas. 
GEOLOGIC HISTORY OF THE KOOLAU RANGE 
The various topographic contrasts within 
the Koolau Range, to which attention has 
been called, lead to modifying the history of 
the Koolau Range as heretofore envisioned 
(Dana, 1890: 301; Dutton, 1894: 212-215; 
Hitchcock, 1900; Hitchcock, 1911: 42-44). 
(The history of the Waianae Range is omit- 
