ON THE GEOLOGY OF BARDADOS. 231 



find clinlcodony of various colours ; and he express!}' stntes that 

 these are different from tlie siliceous fossils of the " Cliert," a hard 

 si.lintery rock ^vhich he describes as "subordinate to the lowest 

 lu'ds of the calcareous formation." He regards this Chert as part of 

 llie ^farl formation, though he was at first inclined to consider it 

 older. The facts he mentions are indeed (juile consistent with the 

 view that it is older, and that it is enveloped by the coral-rock 

 which thus sometimes seems to lie below it. Prof. Duncan takes the 

 same view, for he says that the Chert occurs in masses of limited 

 extent, and has evidently suffered from various wearing causes 

 during the deposition of the Marl. This conclusion is confirmed hy 

 the difference in the fossils of the two formations; the moUusca are 

 not the same, and out of twelve species of corals found in the Chert 

 only one occurs also in the Marl. 



Kcference to the Admiralty chart shows that Antigua stands on 

 the southern edge of a large submarine plateau, and that soundings 

 of less than 20 fathoms extend continuously over a large area to the 

 north and north-west of the island. On this plateau there are 

 numerous coral-growths some of which are covered by one to five 

 fathoms of water, others are marked " coral heads nearly dry,"' and 

 others are reefs dry at low water. 



Off the north coast of the island, for a distance of nine miles, 

 there is a series of such reefs and shoals divided by narrow channels 

 which open into a wide inner channel, where the depth varies from 

 to 8 fathoms. The conditions here are very favourable for the 

 growth of coral, for no rivers debouch on the shore, and there can 

 be little doubt that the reefs are still growing. Eventually they 

 may form a true barrier-reef on a small scale, separated from the 

 shore by a navigable channel ; for this is evidently kept open by 

 the currents running through it, and, though the nature of the 

 bottom is not indicated on the chart, the soundings show that it 

 has a smooth and even floor, which doubtless consists of coral- 

 sand. 



(c) Barhuda is a low bare island, lying about 35 miles north of 

 Antigua, and of rather smaller dimensions. It is thus described by 

 Dr. Nugent in a letter to Mr. Greenough in 1818 * : — " This island 

 is perfectly fiat, and scarcely elevated above the level of the sea, 

 except in one corner, where it rises to the height of 117 feet. It is 

 entirely composed of limestone, which for the most part is perfectly 

 naked and bare, whilst in no place is the depth of soil greater than 

 two or three snakes (s?r), and this is lodged generally in the clefts 

 or cup-like cavities worn in the surface." 



" I send herewith specimens of a compact white limestone [from 

 the neighbourhood of the castle and settlement]. It abounds with 

 fossil shells, belonging principally to a small species of Bulla. 

 Other shells also occur in it less abundantly, of which the following 

 genera have been ascertained, — Area, Cardium, Oliva, TurrlteUn^ 

 Vohita, Stromhiis ; also two species of Madrepore." He observes 



* Trans. Geol. See. 1st ser. vol. v. p 474. 



