The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1885-1921, 1885-08-06

save that the ridges tend inward in
stead of radiating outward.
The NE. pinnacle which over
hangs, is s69 feet high, with possible
error of 10 feet. The highest NV.
pinnacle is goo feet, with possible
error of 20. Had third station been
occupied, the element of error would
have been minimized. trust shortly
to submit to you a finished map of
the island.
In respect to the geology Of Nihoa,
I regard the evidence as complete and
conclusive, that it is the small re-
manning portion of an extremely
eroded and deeply submerged volcanic
dome homologous with the larger
islands of.the Hawaiian group which
still survive in their various stages
of present upbuilding, recent extinc-
ton of volcanic activity, less or more
advanced erosion, and slighter or
deeper subsistence. would not place
undue stress on the very obvious fact
of progressive extinction from NV.
to Sc, nor of progressive increase of
atmospheric erosion from Sc. to
NV, nor of apparently deeper sub
sidence progressing in the same di
rection, nor of Nihoa being equidistant
with the other main volcanic centers
of the chain, all which would lead
US to look to the site of Nihoa for
volcanic center still more ancient
than Kauai.
For positive evidence we must take
the form and structure of the island
itself. In the first place, the sub
stance of the island is homogeneous
with the substance composing the
central interior portions of Oahu and
Maui, as seen in their inner ridges
and pinnacles where the deepest ero-
sions have most thoroughly eaten
down to the hearts of their ancient
domes. / have uniformity found
those interior formations not basaltic,
but scoriaceous. It appears that dur
ing the period of upbuilding, clink-
cry and scOriaceous ejecta pile up at
the center of the volcanic dome and
form its core, while the Outf1owing
streams of lava build up its circum-
ference in layers of more Or less ba-
saltic formation. Nihoa seems to be
pair of clinkery pinnacles out of the
inner core of once mighty dome
which has been eaten down by winds
and rains for thousands of feet, and
DURING IInrockO ned apaS
But the conclusive evidence in my
view is the presence of the numer-
Gus parallel basaltic dikes, which, as
stated above, cut the island from
end to end and from summit to base.
Such dikes can only be produced by
lava during an eruption, rising and
filing thin assures such as an earth
quake might produce across the mass
of the dome. Possibly each dixie may
be the work of "a separate eruption of
the volcano. At any rate q great
period must have elapsed between
the slow piling up of the successive
irregular strata of scoriae, and the
later splitting aud diking of the
whole mass.
Such dikes / have found as char
acteristic accompaniment of the in
terror scoriaceous cores of our noun
tains. Many persons must have OBJ
served the very fine specimen of a
basaltic dixie intersecting the road
down the Nuuanu pail. Some splen-
did specimens cut obliquely across
the inner scoria piles Of Olowalu
and Ukumehame canyons on West
Maui, striking in parallel lines I'M
deviatingly across ridge and chasm,
and rearing sharp crests above the
heights. Some of our Nihoa party
may remember a succession Of high
ridged PERPENDICULAR steps on the
main left hand slope. Those were
the lower faces of several parallel
dikes cutting across the ridge.
From the great number of these
dikes, I infer very protracted Pc
Rod of volcanic activity. From the
closeness with which they stand,
perhaps forty or fifty cutting across
the island, I infer that we are leok-
| ing far down in the deep heart or the
former dome, where dikes would be
| thickest.
AS to probable subsistence, some
thing may be inferred from the fact
that all outlying peaks and ridges
have disappeared from what the
presence of the sharp, hard, thick-set
dikes proves to have been once a
dome of considerable extent at least.
Nihoa seems to be the sole submerged
| pinnacle.
The peculiar contour of the ridges
running down towards each other
seems very significant. This is pre-
| cisely the contour of the heads OF
the leeward valleys descending from
the peaks on either side of Nuuanu
Valley. 1t is the anaphitheater form
which Captain DuttOn shows to be
the natural evolution of the heads OF
ravines of atmospheric erosion.
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