The Hawaiian gazette., 1894-01-16

lulu offers to the student of historical
geology many most interesting prob
lens. The origin of the soil of Homo.
lulu is one of these. Elsewhere in
Hawaii nei the soil consists gener-
ally, except in the valley bottoms,
simply of decomposed lava, fragments
of the unaltered rock everywhere
encumbering the ground. Here and
there only do We find areas of deep
soil free from stones. These are
mostly in nearly level regions, where
frequent rains have favored the rot
ting of the rock to considerable
depth, while the amount of rainfall
has been insufficient to carry off into
the ocean the disintegrsted rock. In
q few cases a deep soil has been
formed from decomposed volcanic
sand or gravel, which has been spread
by an explosive eruption over large
area of land. Honolulu owes its fer
tile grsvelly soil to an occurrence of
this kind, so recent that much of
the gravel remains still undecom-
posed. 1t is easy to see that the re-
msrkable group of cinder cones just
back of the city are geologically
quite new. Loose as is the material
composing them, erosion has made
little progress as yet in scoring their
sides, in spite of such flooding rains
as we have had twice within ten
months past-upwards of five inches
ID each storm.
Additional proof of the regency of
the eruption or eruptions which
heaped them up is found in the pres
ence in portions of the tufa forma-
ton at the base of Tantalus of salt
in large quantity, although the loca-
ton is one where the soil is kept
constantly damp by frequent rains,
and there must be rapid drain on
the salt supply. as the fresh rain
water percolstes through the tufa.
The salt itself, 1 think it may be as
sumed, has come from sea water, ad-
mitted into the fssure which formed
at the time Of the eruption, although
it seems remarkable that water so
admitted should find vent at SO great
an elevation and at such a distance
from the sea. The tufa of Diamond
Head is also impregnated in places
with salt, one of the spots being near
the very top of the cone, and in this
instance there would seem to be no
question as to how it came there.
There is another incidental evi-
dence which l may mention of con
nection of the sea with the eruption
in Makiki, in the large amount of
calcareous matter that has been de-
posted here, apparently from hot
springs. There is near the Makiki
fall bed Of rock many feet IN thick
ness, consisting of volcanic gravel
cemented together with calcium
carbonate. 1t is in fact this ledge of
hard rock which has made the fall
Now our volcanic rocks contain so
small proportion of lime that it
does not seem likely that water, even
at high temperature, would dissolve
out from them sufficient OF that min
eral to account for any such deposit.
The water which came up through
the coral formation underlying Dia
mond Head We know was mighty
charged with lime, and we may res-
son that this water also came through
a assure trayersing coral rock. 1t is
noticeable that in both instances the
carbonate of lime is accompanied also
by phosphate, but this is very com
mon association of minerals.
When these large mounds of vol
canic sand were piled up some of the
same material was widely scattered,
falling over the region to leeward, as
far as the harbor on the west, and
Punahou street on the south, but
mainly in the line of the trade wind,
passing Lunalilo Home, the powder
magazine and the south shoulder of
Punchbowl. Whether the black
sand on the side of Punchbowl and
in its crater was from this source or
from Punchbowl itself, and so older,
is not quite certain. That such mate
rial occurred among the eiecta from
that crater is beyond doubt, as may
be seen by examining the exposed
strata in the gap on the east side OF
the cones. 1t is hardly probable,
however, that any such formations
remain now superficial
The mouth of Makiki valley must
have been closed by the sand heap,
the stream thus damned up after a
time cutting through the obstruction,
which was in places fifty feet or more
in depth, and spreading the sand
thus removed over the fiat below.
Query, was this fiat at that time still
submergedi 1 have found no where
as yet conclusive evidence of this. l
am inclined to believe that the erup-
tions were coincident with the change
of level which made it dry land
The wash from the hill sides has
also carried down much gravel and
scattered it in a similar manner, so
that the plain is covered to depth
Of five to fifteen feet over an extern
sive area with the debris, from which
has been formed a deep rich soil.
Where this debris has been cut into
by streams or bitches, there are found
frequently in it deposits of calcare-
- i. n