464 Mr. H. B. Guppy on Coral-soundings 
on the protected sides of islands by the arborescent Madrepores. 
The branching coral most frequent in the greater depths was 
a slender Madrepore, fragments of which, bearing the living 
polyps, came up in the arming from depths of 93, 10, 
and 13 fathoms. I should add that a portion of an Alcyo- 
narian (Anthelia), was brought up from 13} fathoms. 
6. The Barrier-reef of Choiseul Bay.—This bay lies within 
a broken line of barrier-reef which skirts the western extremity 
of the large island of Choiseul, at a distance of from one half 
to three quarters of a mile from the shore. Basing his obser- 
vation on Bougainville’s chart of this bay, Mr. Darwin inferred 
(‘ Coral Reefs,’ p. 167, edit. 1842) that part of the shores is 
fringed by coral-reefs. In reality the reefs have the charac- 
ters of the barrier class, although associated with shore-reefs 
to the northward and southward of the bay ; and the capacious 
anchorage with adepth of from 13 to18 fathoms, which Choiseul 
Bay affords, owes its existence to the fact of its lying within 
a line of barrier-reef. ‘The intention of the French navigator 
to anchor in this harbour was frustrated by an attack made 
by the natives on his boats whilst employed in searching for 
an anchorage. For this reason his plan of the harbour was 
imperfect, and may be viewed as merely a preliminary sketch. 
My soundings off this barrier-reef gave results somewhat at 
variance with my previous experiences. I was surprised to 
find that in fifteen casts between the depths of 3 and 20 
fathoms sand or gravel was brought up on the arming on 
seven occasions, and that six out of fourteen casts in depths 
between 20 and 40 fathoms gave a similar indication of the 
bottom. A living fragment of Madrepore was brought up 
from 13 fathoms. Ina cast of 23 fathoms the arming pre- 
served the impression of the cells of one of the Astreide, and 
in another of 31 fathoms there was a rounded impression of 
the size of a billiard-ball, the inner surface of which retained 
the prints of small cells as if of a Porites. The conclusion 
at which J arrived after extending my soundings to 40 fathoms, 
at a distance of about 600 yards from the shore, was that I 
had not reached the lower limit of the coral-zone. An exami- 
nation of the configuration of the bottom, as shown in section 3, 
may throw some light on this unusual experience. With the 
eye assisted by the lead I could observe that the submarine 
portion of the reef at first sloped gradually to a depth of 4 or 
5 fathoms. There was then a sudden drop of another 9 or 
10 fathoms, forming a steep declivity, at the foot of which 
began a broad platform with a gentle slope down to 25 fathoms, 
and terminating in another somewhat gradual slope. An 
inspection of this diagram would lead one to expect that an 
