58 DR. H. B. GUPPY. 
angle from the 100-fathom line to a sounding of 1,200 fathoms 
is about 15 degrees. 
I have taken the foregone examples because they illus- 
trate the various kinds of barrier-reefs surrounding large 
islands. The instances of New Caledonia and of Florida 
might have been similarly cited. JI have, however, gone far 
enough to show that barrier-reefs have, as a general rule, the 
appearance of being situated at the edge of a submarine ledge 
or plateau. There are two different explanatious of this ap- 
parent position of barrier-reefs that readily present themselves 
to the mind. 
The first is that of subsidence, which Mr. Darwin offers in 
his theory, the shore-reef by such a movement becoming a 
barrier-reef separated by a deep channel from the coast. In 
the instances before cited of the great Fiji barrier-reef and of 
the reef of Bougainville Island in the Solomon Group, this 
explanation, however, is at once negatived, because these 
localities are situated in regions of upheaval, where coral reefs 
and their foundations have been lifted in recent times to 
heights of several hundred feet above the sea. 
The second explanation is that advanced by Mr. Murray in 
his new theory. By him this plateau-like appearance is attri- 
buted to the seaward growth of a barrier-reef on its own tahis, 
whilst the lagoon-channel is being formed by the decay and 
solution of the coral. Though well convinced of the fact of 
the seaward growth of reefs, and of the important influence 
of solution, I scarcely consider the outward growth to be 
sufficiently rapid, or the effect of solution to be sufficiently 
great, to explain the situations of such distant barrier-reefs as 
those fronting the east coast of Australia and the north side 
of Viti Levu in Fiji. Both Darwin and Murray would 
associate the formation of the so-called submarine ledge, 
from the margin of which a barrier-reef appears to rise, with 
the history of the reef. The question now arises whether 
the position. of a barrier-reef at the edge of a submarine 
plateau is apparent or real; or, in other words, whether there 
was a submarine ledge before the coral reefs began their 
growth. 
To this question I expected no answer; but, after examining 
the submarine profile of the east border of Australia, from 
Cape York to Cape Howe, I obtained a very unexpected reply. 
There at once opened up before my imagination a new road 
towards the solution of this problem; and I think when I 
have pointed out this new method of investigation, which 
consists in comparing the profile of a coast outside the region 
of coral reefs with that of the continuation of the same coast 
