in the Solomon Islands. 463 
at the 100-fathom line, having no reliable information of the 
greater depths. Santa Anna, [ should add, rises out of deep 
water, where 200 fathoms of line have failed to reach the 
bottom. 
3. The Reef of Onua Islet—This islet is one of a group of 
islets and small islands situated on a broken line of barrier- 
reef which skirts the weather or south-east border of the 
Shortland Islands. My soundings were taken off the weather 
edge of this reef in a ‘Rob Roy’ canoe, and considerable 
caution had to be exercised in the shallower depths on account 
of the uncertain behaviour of the rollers. From a series of 
soundings between the depths of 6 and 33 fathoms, it would 
appear that the lower limit at which coral thrives on the sea- 
ward slope of this reef is about 20 fathoms. Beyond that 
depth the arming was thickly coated with sand and gravel, 
Section 2 shows on a true scale the submarine contour of this 
reef where the soundings were taken. Tor the first 100 yards 
from the edge of the reef-flat there was a gradual descent 
until a depth of 5 or 6 fathoms was reached, when there was 
a rapid fall of from 10 to 15 fathoms, followed by a moderate 
slope to the 100-fathom line. 
4, The Harbour of Treasury Island.—In this harbour, 
which has a maximum depth reaching down to 46 fathoms, I 
found the living coral restricted, on account of the rapid 
descent of the submarine slope, to a narrow zone limited by 
a depth of from 12 to 15 fathoms. In the more open part of 
the harbour a calcareous mud, often foraminiferous and occa- 
sionally loamy, and derived from the material brought down 
by the streams, formed the bottom beyond the coral zone; 
but among the islets in the more sheltered south side of the 
harbour I found that calcareous gravel derived from the débris 
of corals and shells occurred in the deeper water. 
5. North-west Coast of Baldlai Island, Bougainville Straits. 
—This low island is of raised coral formation and fringed by 
shore-reefs. My soundings (over sixty in number) were 
taken off the north-west coast, which is the lee side of the 
island during the greater portion of the year. A depth of 
15 fathoms apparently represented the lowest limit of the 
zone of corals. Beyond that depth the arming, in the great 
majority of the casts, came up thickly coated with calcareous 
sand and gravel. My soundings showed that extensive 
thickets of a branching Porites (Porites lavis, Dana) oc- 
curred in the shallower depths of from 2 to 8 fathoms, living 
fragments frequently breaking off inthe arming. ‘This species 
of coral apparently occupied the region that is usually usurped 
