Fesruary 18, 1897] 
NATURE 375 
o 
end. Had we been provided with 4-inch tubes we could have 
made a fresh start, and might have descended another 30 or 40 
feet, bu ‘even then ultimate success would not have been 
ensured, for the chance of meeting again and again with inter- 
mixed sand and coral remained always open, and every such 
encounter would have required lining tubes of diminished 
calibre. 
Baffled in all our endeavours, and no other part of the island 
offering more hopeful prospects of success, we had no alternative 
but to abandon the undertaking, and on July 30 we were taken 
from the island in the Pezgzen and returned to Fiji. On 
landing there we had the mortification to learn that additional 
apparatus was then on the way to Funafuti, our friends in 
Sydney having, with great generosity, at once despatched 
machinery for driving in sand on receipt of a letter I had sent 
informing them of the failure of our first borehole. We had 
had no reason to expect such spontaneous assistance, and even 
had we been fortunate enough to have remained on the island 
till the machinery arrived, we should probably not have 
accomplished the object we had in view, though we might 
possibly have carried the borehole down to a depth of about 
400 feet. 
A very free communication must have existed between the 
borehole and the sea, for whenever a big roller broke upon the 
reef the rods lifted, and after the lining had been withdrawn, 
water spurted out of the borehole with the fall of every wave. 
The open nature of the reef is further in- 
dicated by the fact that the sea-water rises 
with every tide to fill certain depressions, 4200 
. The most important contribution, however, and one that I 
think must, in certain details greatly modify our views as to the 
nature of coral reefs, is afforded by the investigations of Captain 
Field. Never before have soundings, both within and without 
an atoll, been so closely and systematically made, and the results 
seem to me commensurate with the care and pains that have 
been taken to secure them. Four series of soundings, ‘ Sec- 
tions,” as they are termed on board the Penguin, have been 
run from the seaward face of the reef outwards. How close 
together the soundings were made is shown in the following 
table, which Captain Field has kindly permitted me to copy 
from his order book :— 
Depth o— 40 fathoms every 10 yards. 
» 40— 70 ” 20 5, 
” 7O0—100 ” 39 55 
” 100—I50 ” 49 5, 
58 I150—200 5 50" 55 
55 200—300 5 60 ,, 
» 300—400 ” 79 355 
3 400—500 » 80 ,, 
. ” 500—600 bh) 90 ” 
5, 600—700 » 100 ,, 
“ 700—8o0o A 200) 5, 
The profiles obtained by the four series are closely similar, 
and, as regards one important feature, almost identical. This 
4000 800 
which occur in many places in the middle 
of the island; as the tide ebbs this water 
flows away down fissures, often so rapidly 
as to form little whirlpools. 
Wherever I have seen the reef growing 
it has always presented itself as clumps or 
islets of coral and other organisms with 
interspersed patches of sand, and the 
borings would seem to indicate that it 
maintains this character for a very con- 
siderable depth, and possibly throughout. 
The structure of the reef appears indeed to 
be that of a coarse ‘‘ sponge” of coral with 
wide interstices, which may be either empty 
or filled with sand. 
As regards the nature of this ‘‘ sand,” it 
is important to observe that it does not 
consist of coral débris ; this material and 
fragments of shells forming but an insig- 
nificant part of it ; calcareous algee are more 
abundant, but its chief constituents are 
large foraminifera, which seem to belong 
chiefly to two genera (Oréztol/étesand Ttno- 
porus). Tt covers a considerable area of 
the islands, and has accumulated during the memory of the 
inhabitants to such an extent as to silt up certain parts of the 
lagoon. This and the abundant growth of corals and calcareous 
algee, such as Halimeda, lead to the belief that the lagoon is 
slowly filling up. 
A suggestion has recently been made that more light is likely 
to be thrown on the history of atolls by a study of ancient 
limestones in the British Isles than by boring in existing reefs. 
The first essential, however, for such a study would appear to 
be a knowledge of the structure of living atolls, for, without 
this, the identification of others forming a part of the earth’s 
crust, might remain more or less a matter for conjecture. So 
far as the structure of Funafuti has been proved by borings, it is 
scarcely what a field geologist might have anticipated, and if 
deposits of a similar nature and origin should have been encoun- 
tered in, say, the mountain limestone, it is doubtful whether, 
previous to the borings in Funafuti, their interpretation would 
have been easily reached. 
While the boring has proved a failure, the other objects of 
the expedition have been attained with complete success. 
Messrs. Hedley and Gardiner have made a thorough investi- 
gation of the fauna and flora, both land and marine. Dr. 
Collingwood has obtained a good deal of information of ethno- 
logical interest, and we all have brought home a fairly com- 
plete collection of native implements and manufactures. A 
daily record was kept of maximum and minimum temperature, 
and of the readings of the dry and wet bulb thermometers. 
NO. 1425, VOL. 55 | 
200 
Wis ‘0 
iY oH 
fphih, 
WG AAT 
| wa VN | TT TT Vg 
YM V 
Wi? 5 
290 
500 
aonked ZA Be 
Fic. 3.—Section D—Horizontal measurements in yards ; vertical measurements in fathoms. The 
section is drawn to true scale. 
is the sudden change in slope that occurs at or about 140 fathoms. 
Speaking generally, one may describe Funafuti as the summit 
of a submerged conical mountain, the base of which, at a depth 
of 2000 fathoms, is a regular ellipse, 30 miles long by 28 miles 
broad. It rises witha very gentle slope, which gradually grows 
steeper as it ascends, till from 400 to 140 fathoms it has an 
angle of 30°; at 140 fathoms an abrupt change occurs, and the 
slope becomes precipitous, making an angle of from 75° to 80° for 
the greater part of its course, tillit passes into the shallow flats ot 
the growing reef. It is difficult to resist the impression that it 
is the upper 140 fathoms (840 feet) which represents the true 
coral reef. A convex curvature of the profile between 166 and 
261 fathoms is probably a talus, produced by an accumulation 
of coral débris (Fig. 3). 
The conical mountain below the 140 fathoms line, with its 
parabolic slope, is suggestively similar to a volcano ; but, if so, 
its crater must have been immense, 10 miles across at least. A 
volcano, 12,000 feet in height, with a crater 1o miles in diameter, 
is, however, not an unknown phenomenon ; within the limits of 
the Pacific we may cite Haleakala, in Maui, Sandwich Islands, 
as closely comparable. 
A part of my work while on the island was the construction of 
a geological sketch map, part of which is shown in Fig. 4; its 
interest chiefly centres in a broad expanse near the Mission 
Station, where the two narrow limbs of the island meet, or, if it 
be preferred, whence they extend. Towards the seaward side 
this broad corner is occupied by a mangrove swamp, the floor of 
