202 MR. JUKES-BROWNE AND PROF. HARRISON 



Bath there is no reef-coral heyond the three-fathom line, which is 

 about 590 yards from the shore ; from this line there is a steep 

 slope to 13 fathoms, and then a plateau gradually deepening to 24 

 fathoms, heyond which is another steep slope down to 100 fathoms. 

 This is the typical contour of the coast opposite the Scotland Dis- 

 trict, and the line of 24 fathoms is nearly parallel to the line of 

 100 fathoms, showing the regularity of the profile. In the shallow 

 water down to 24 fathoms the bottom is generally sand ; beyond 

 that it is generally mud. 



The profile above described is shown in fig. 2 by the lower line 

 AB, while the upper line is a profile drawn in the same direction 

 half a mile south of the first through the beginning of the coral- 

 plateau. A comparison of the two profiles at once suggests that the 

 coral-reef has been built upon the sand-plateau shown in the lower 

 profile, and that it was limited by the seaward extent of this pla- 

 teau ; further, that the coarse sand which extends in the upper 

 profile to the line of 60 fathoms is a product of the waste of the 

 coral-reef, and we may infer that, if any part of this were raised to 

 within 25 fathoms of the surface, reef-corals would begin to grow 

 upon it. So close together are the two lines of section that we may 

 even take the distance between the two outlines as giving some 

 guide to the thickness of reef which has here grown up on the sand- 

 plateau ; it is from 10 to 12 fathoms, i. e. 60 to 70 feet. 



Prom this locality the submarine coral-plateau extends round the 

 eastern part of the island. It varies in width, but always has a 

 steep outer slope, plunging down from 10 to 20 or 25 fathoms. 

 Opposite Kitridge Point the plateau broadens out and becomes at 

 the same time divisible into two stages or shelves, an inner one 

 covered by 2 to 4 fathoms of water, and an outer one covered by 6 

 to 10 fathoms (see fig. 3, upper line). 



South of this two new features commence, and both are very 

 noteworthy. The first is, that a part of the reef within the four- 

 fathom line rises to the surface and forms what is known as the 

 Cobbler's Keef, which, with other similar reefs, forms a nearly con- 

 tinuous outer reef along the south-east coast of the island as far as 

 South Point. The Cobbler's Keef at its north-east end has a breadth 

 of more than half a mile exposed at low water, but it narrows to 

 the south-west, and, though the reef itself is a continuous ridge, 

 there are places where it does not quite reach the surface, leaving 

 gaps covered by one or two fathoms of water. Between this outer 

 reef and the discontinuous shore-reefs there is a shallow channel 

 having an average depth of 3 or 4 fathoms ; it is very wide near 

 the eastern end of the island, where the coral-growth seems to find 

 its maximum development, and extends to a distance of a mile and 

 three quarters from the shore. 



The second feature above alluded to is the appearance of a chan- 

 nel in what may be called the nine-fathom ledge, i. e. the lower 

 coral-shelf on which the water has an average depth of 9 fathoms. 

 This channel commences opposite the northern end of the Cobbler's 

 Beef, and becomes both wider and deeper to the south-west, leaving 



