496 PROF. J. W. SPENCER ON TSE GEOLOGICAL AND [NoV. IQOI, 



YI. The White Limestones or Antigua Formation. 



The north-eastern portion of the island is underlain by a white 

 limestone or marl, which is the 'Marl.' formation of Nugent 

 (or the ' Upper Limestones and Marls ' of M. Purves). This 

 formation is composed of an earthy marl and beds of compact 

 limestone, often hard and durable enough for building purposes. 

 White is the prevailing colour, but it is sometimes greyish or 

 yellowish in the lower beds. The limestones are distinctly bedded, 

 and dip from 12° to 20° north-eastward; but the bedding in the 

 earthy or marly beds is often obscure. These varieties of rock 

 pass one into the other. This formation is apparently conform- 

 able to the underlying tufaceous beds. The thickness of the 

 limestone was not determined, but there still remain of it at least 

 many hundred feet. The limestones are in part capped by a 

 mechanical deposit, which has not been distinguished from the 

 limestones by any previous observer. This series gives rise to 

 the undulating hilly country occupying the north-eastern part 

 of the island, the rolling features of ■^^'hich are the remains after 

 the enormous degradation of the limestone at a comparatively 

 slight altitude above the base-level of erosion. From the dip of 

 the strata it naturally follows that the slopes towards the south- 

 west are somewhat more abrupt than in the opposite direction. 



The importance of this formation arises from two facts : — first, 

 that it was the last great accumulation before a very long period 

 of denudation, which removed not only a large proportion of the 

 limestones themselves, but also exposed the older features ; and 

 secondly, on account of its containing a fauna by which the age of 

 the beds can be determined. The question is not one of local 

 distribution on the island, but rather one concerning the whole 

 North-eastern Antilles, as showing that the phenomena described 

 did occur in that region, during the geological periods ascertained. 

 These limestones generally form the summits of the higher hills, 

 but at the lower altitudes they have their very much eroded 

 surfaces covered by a thin mantle of mechanical deposits, 

 wliich have sometimes been removed in artificial cuts and 

 otherwise. 



At the north-western end of this belt, the sea has encroached 

 upon the high lands, where at Wetherell Point it has formed a 

 bluff about 100 feet high. Here both the hard and the marly beds 

 occur, each being highly fossiliferous in places. Some of the harder 

 beds appear to be made up of Ostrea. There are also other species 

 of molluscs, but they are mostly in a poor state of preservation, 

 and seldom consist of more than casts. The most important fossils 

 found here are the smaller corals which predominate in the softer 

 beds and are often silicified, thus preserving the structure so as 

 to be determinable. I observed fossils at other localities, but 

 nowhere so abundant as at Wetherell Point. The only corals 

 that have hitherto been collected were those sent by Nugent to 

 London in 1819, and studied by Duncan, who enumerates eleven 



