204 MR. JUKES-BROWNE AND PROF. HARRISON 



the outer part of the nine-fathom ledge to form a narrow ridge or 

 M-all which rises steeply on both sides from depths of 18 or 20 

 fathoms (see fig. 4), This submarine ridge is roughh' parallel to 

 the outer reef above mentioned, and is perfectly continuous for a 

 distance of about twelve miles, ending nearly opposite the termina- 

 tion of the surface-reef off the south point of the island; it is in 

 fact a submarine barrier-reef, for if it was built up to the surface 

 there would be a navigable channel inside it. 



This submarine ridge or wall appears to consist everywhere of 

 growing coral, and the usual depth of water above it is 8 or 9 

 fathoms, but in some places there are only 6 fathoms ; as limited 

 by the ten-fathom line its top is about 100 yards broad, varying 

 frcm 80 to 150 yards. On the outside there is always a steep 

 slope, and sometimes dejDths of 18, 20, or 22 fathoms are marked 

 close to the ten-fathom line on the chart, with depths of 25 to 

 30 fathoms within 100 yards. On the inside the slope appears 

 to be equally steep, often dropping from 10 to 20 fathoms in a few 

 rods' distance, and in one case 23 fathoms is marked close to the 

 inside wall. 



The average depth of the channel inside this submarine wall is 

 20 fathoms, and its average width about half a mile ; the bottom is 

 nearly everywhere sand, sometimes fine and sometimes coarse, which 

 is no doubt calcareous coral-sand derived from the outer fringing- 

 reef which comes within the constant action of the breakers. On 

 the inner side of this channel the bottom rises rapidly to the ten- 

 fathom line, from which there is a more gentle slope to the four- 

 fathom plateau. 



From the above description, and from the profiles in fig. 4, it is 

 evident that the Cobbler's Reef is a portion of the four-fathom 

 plateau which has grown up to the surface, and that the submarine 

 barrier-reef is a ridge-like continuation of the nine-fathom plateau 

 which exists to the north of Kitridge Point, Moreover, as the 

 development of the submarine barrier commences opposite the 

 point where the Cobbler's Eeef begins, it would seem that the one 

 is in some way connected with or dependent on the existence of 

 the other. 



Prof. Semper has sought to explain the conformation of growing 

 coral-reefs by the influence of currents, and states " that wherever 

 constant and deep currents impinge on a coast at an angle, the 

 reef will inevitably grow upwards perpendicularly if the force of the 

 current be sufficient " *. Now the current of the Gulf-stream im- 

 pinges on the eastern coast of Barbados, the local currents forking 

 against the eastern point, and running at 1^ knots an hour both to 

 the X.AV. and the S.W. ; if therefore the peculiar conformation of 

 reefs along the south-east coast were due to the action of currents, it 

 should be the same along the north-east coast, where for some dis- 

 tance similar conditions prevail, the current in both cases impinging 

 at an angle and having the same velocit}'. This explanation will 

 consequently not apply to Barbados. 



* 'Animal Life/ 3rd edition, p. 265, Internat. Science Series. 



