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APPENDIX II. 
but was observed at similar depths in the case of others. 
Between such submerged reefs and those marked on the 
surface by a reef flat, with its accompanying islet, or by a 
sand key, intermediate conditions were not found, and Mr. 
Guppy is of opinion that reefs on arriving within from 4 to 
8 fathoms from the surface have reached the limit of their 
upward growth, and afterwards have to extend laterally. 
Hence he infers that detached submerged reefs are unable 
to raise themselves within the limit of constructive breaker- 
action without the assistance of a movement of elevation. 
Of such a movement, in this region, there are certainly 
proofs, and the same is the case in the Low Archipelago, 
the Fiji and Pelew groups. 
Among the reefs which have reached the surface in 
the Solomon Archipelago, fringing and barrier reefs are 
much commoner than atolls. ‘ A line of barrier reef pro- 
bably not much under 60 miles in length, and having in- 
numerable islets on its surface, fronts the eastern coasts of 
the islands of New Georgia at a distance of from 1 to 3 
miles from the shore. At St. Cliristoval the fringing reefs 
occasionally reach a mile in breadth, but usually do not 
exceed a quarter of a mile. The 100 fathom line lies 
generally about 1,200 yards from the edge of the reef flat 
which would give an average slope of 10°.’ Upheaval is indi- 
cated by a recently elevated flat of coral rock, which is in 
some places 15 feet or so above high water level. North 
of St. Cliristoval are three small islands (named the Three 
Sisters). They commenced their growth, according to 
Mr. Guppy, as submerged flat-topped reefs, like those 
already mentioned. They were then elevated to about 
70 feet above the sea, and have since assumed an atoll 
structure. He regards them as ‘ based on three submerged 
peaks which lie at some unknown distance below the sur- 
face.’ They are enclosed within the same hundred fathom 
line ; the submarine slope at first is gradual and then 
