of Edinburgh, Session 1885-86. 
899 
brought up from depths between 200 and 400 fathoms were usually 
either a dark calcareous mud or a dark mud containing but little 
lime. In places the bottom seemed to be rocky with but little sedi- 
mentary matter. 
I here append a few of the soundings which appear to be of special 
interest : — 
420 fathoms. — Gravel (size \ of an inch) formed of a somewhat 
decomposed volcanic rock. A single valve of a delicate 
shell ( Leda , sp.) was also brought up. 
370 fathoms. — An almost impalpable dark-coloured n on-calcareous 
mud or clay, of which a large portion appeared to be of 
vegetable orign, a low plant-growth or alga investing the 
minute siliceous grains. 
350 fathoms. — A subangular fragment (J an inch across) of some 
calcareous rock, with a portion of the shell of one of a species 
of the Balanidae apparently recently fractured. 
230 fathoms. — A single subangular pebble, almost an inch long, 
of a finely crystalline basic volcanic rock (spec. grav. 2*85). 
No accompanying mud or sand. 
170 fathoms. — Small angular, probably crushed, fragments of 
an inch) of a dark compact calcareous rock. 
From the several soundings that were made between 100 and 400 
fathoms in this locality, I came to the conclusion that the volcanic 
muds, which form the bulk of such islands as Ugi and many others 
in the Solomon Group, are at present forming off the coasts of 
reef-girt islands in depths greater than 100 fathoms. In the case 
of those portions of the coasts of the large islands, such as St 
Christo val, which on account of the sediment brought down by 
the streams are bare of reefs, the soundings of the survey have 
shown that these volcanic muds are forming at all depths from a 
few feet beneath the low tide level to a depth of some hundreds of 
fathoms. 
Some of the principal points of this paper I will briefly summarise 
as follows : — 
1. That f ringing-reefs, barrier-reefs, and atolls exist in this group. 
They arrange themselves into two classes (a), those formed at 
the present sea-level, and ( b ) those that have been upheaved to 
