208 ME. JUKES-BROWXi: AND PKOF. HAKRISON 



plateau, and two outer reefs rising to within 7 fathoms, separated 

 from this plateau by channels of 10 to 20 fathoms deep. The 

 inlets have a bottom of sand and mud, which has doubtless been 

 brought in from the land during the occasional heavy rains which 

 are common in Barbados. Several gullies converge at HoletowUy 

 and as their sources are on the Hillaby range at elevations of 900 

 to 3000 feet, and only five miles distant, their channels have a 

 rapid fall and they probably have brought down large quantities of 

 detritus, the influx of which must have affected the growth of the 

 coral. There is, moreover, a permanent flow of fresh water from 

 the Iloletown outlet. 



North of Holetown the submarine profiles are uniformly steep 

 till we reach Maycock's Eay, in the extreme jN^.AV. of the island. 

 Here again the four-fathom line runs out from the shore, ajid there 

 is a wide shallow plateau extending for about four miles to the 

 north-east. From this several reefs rise to the surface, and are 

 exposed to the constant action of the breakers. These are the 

 Harrison Eeefs, and they are comparable to the Cobbler's Eeef at 

 the opposite end of the island. Consequently it is interesting to 

 find a repetition of the same phenomena outside the Harrison Eeefsy 

 namely a lower plateau covered by from 7 to 9 fathoms of Avater, 

 and traversed along the greater part of its length by a channel 

 which is from 11 to 13 fathoms deep ; so that the outer part of the 

 plateau runs out as a wall -like ridge parallel to the inner reefs, 

 forming a submarine barrier-reef like that off the south-east coast. 

 These features cease at the northern end of the island, and the 

 submarine profile gradually changes to a continuous slope with 

 very little coral-growth. The extreme northern and north-eastern 

 coasts are backed by ranges of rugged cliffs, with promontories and 

 detached rocks, features which clearly indicate erosion and recession 

 of the coast-line, 



From the above account of the coral-reefs that are now growing 

 round the shores of Barbados, we learn several facts which throw 

 light on the structure and conformation of the raised reefs and 

 limestones that cover so large a part of the island. In the first- 

 place it would appear that reef-corals can certainly build up from 

 a depth of 25 or 30 fathoms, so that, supposing they continued to 

 flourish for a sufiicient length of time wdthout any movement of 

 the land, they might build a reef which would have a thickness of 

 180 feet. 



Secondly, we find that there are always deposits of coral-debris 

 and calcareous sand in front of the lowest reefs ; so that, if the aref* 

 were elevated, this would come within the limit of reef-coral 

 growth and would form the foundation of a new reef. In this way 

 20, 30, or even 50 feet of limestone-material containing coral frag- 

 ments may be formed before any actual reef-growth takes place 

 upon it ; but when raised this would differ from coral-reef rock only 

 in the absence of large masses of solid coral. 



Thirdly, the prevalent outline of the submarine profile is that of 

 shelves or terraces, varying in width according to the slope of the 



