of Edinburgh , Session 1885 — 86 . 
865 
Lark Skoal, a submerged reef which rises between the islands of 
Ulaua and the Three Sisters from a depth of 200 fathoms, is 
covered by a minimum depth of 7 fathoms. It is exposed to the 
full force of the trade-swell, and its position is often marked by a 
dangerous tide-rip. As limited by the 20 fathom line, this shoal 
measures 1 by 1J miles. The numerous soundings obtained by 
Lieut. Oldham and the officers of the “ Lark ” gave no indication of 
a central hollow on its surface. On the contrary, they showed that 
the shoal possesses a comparatively level summit covered by from 7 
to 10 fathoms of wate^. From the ship’s side the dome-shaped 
massive corals could be discerned; and the paucity of branching 
corals was evidenced by the absence of fragments in the armings of 
the lead. In most of the soundings the armings were clean ; but 
occasionally portions of the joints of the calcareous alga, Halimeda 
opuntia , together with coral sand and gravel, were brought up. Out 
of twenty casts taken by myself on both sides of the ship in a depth 
of 9 fathoms, all but three showed clean impressions, and in five of 
them the nature of the coral could be recognised. Two similar shoals, 
lying to the south of Eddystone Island, are described on page 876. 
Other detached coral patches, covered by from 5 to 10 fathoms of 
water, lie close off the south coast of St Christo val ( vide page 870). 
The numerous submerged reefs of Bougainville Strait occur just 
within the edge of the submarine platform, or submerged extension 
of Bougainville Island, which is delineated by the 100 fathom line 
in the recent Admiralty chart. They are generally covered by from 
4 to 8 fathoms of water, and have very level surfaces, over one of 
which the ship dragged her anchor without a check for about half 
a mile. On one of them I brought up with a grapnel from a depth 
of 8 fathoms a portion of a Pocillopora with stout expanded 
branches, which appeared to be the prevailing coral. On another I 
found Psammocora planipora (E. & H.) in considerable quantity in 6 
fathoms, this being the only occasion on which I found this coral. 
From the same depth of 6 fathoms on this shoal, I brought up two 
masses of coral rock, of which the largest, a little more than a cubic 
foot in size, was a fragment of Porites tenuis (V.), for the most part 
dead, and covered by Nulliporce , and extensively bored by molluscs 
and annelids. Small specimens of other living corals were attached 
to it, such as Pocillopora pulchella (Br.), an encrusting Montipora, 
3 L 
VOL. XIII. 
