ON Tin; (;i;()i,o(;v ()i<- u akbados. 21 1 



In m;iny })liiccs banks of eoral-sand and debris appear to have 

 been formed outside a growing reef, and to have accumulated to a 

 greater or less thickness before any true coral-reef grew upon them. 

 Such dctrital rock is frequentl}', if not always, found at the base of 

 the coral-limestone, and its existence will account for the total 

 tliickness of this limestone being in some cases greater than the 

 depth of water in which it is generally supposed that reef-building 

 c-orals can begin to grow. 



So far as we have been able to ascertain, there are not many 

 localities where the thickness of coral-rock exceeds 200 feet. It 

 is generally less than this amount, but does in some places appear 

 to reach a depth of 230 feet ; indeed in one place, namely Eowmans- 

 ton, it is 200 feet, this being the measured depth from the surface 

 at the mouth of the well down to the floor of the cavern into which 

 the well opens, and it is known that the cavern is excavated in 

 coral-rock. 



For the following information relating to the depth of the coral- 

 rock in different places, we are indebted to the courtesy of E. 

 Easton, Esq., C.E., E.G.S., the particulars having been obtained 

 from borings made for the Barbados Water-Sup ply Company. 



A boring made in the gully near Lightfoots, in the parish of 

 St. John's, was carried through coral-rock for 103 feet, passing then 

 into red clay, and finally into Hadiolarian earth 18 feet lower down ; 

 this gully itself cuts about 130 feet into coral-rock, so that the total 

 thickness of the rock below the general surface of the ground must 

 be 233 feet, the height of the ground above the sea being 552. 



Another boring made in the bottom of the gully near Byde Mill, 

 in the same parish, began at a level of 349 feet above the sea, the 

 gully itself being at least 100 feet deep ; the depth of the boring was 

 117 feet, and was still in coral-rock, the thickness of which is here, 

 therefore, more than 217 feet. 



It is noticenble that both Lightfoots and Byde Mill are near the 

 border of a plateau, and consequently along a line where we might 

 expect the reef-rock to be thick and to be based on coral-sand. 



In Cole's Cave gully, on Walk's Spring estate, about six miles 

 N.N.E. of Bridgetown, the level of the gully-floor is 685 feet above 

 the sea, the level of the stream in the cavern below is 576 feet, 

 and the level of the road at the edge of the gully opposite the cave 

 about 752 feet. Here, therefore, there is at least 176 feet of coral- 

 rock, and probably more in some places a little distance from the 

 edge of the gully. 



A boring in the gully between liock Dundo and Zion HiU in St. 

 James's parish reached Radiolarian earth at 41 feet from the surface 

 and at a level of 2(53 feet above the sea, while the road along the 

 top of the gully is 400 feet above the sea, so that the rock here is 

 137 feet thick. Moreover, to the east of this spot there is a very 

 steep slope or escarpment, the top of which is 600 feet above the 

 sea, and though the subterranean water-level probably rises, a 

 section constructed for us by Mr. Hucklebridge (from data in Mr. 

 Easton's office) shows that it is 250 feet below the surface of the 



