^0\. 57.] PHYSICAL DEVELOPMENT OF ANTIGUA. 501 



covered with a thin layer of marly earth, containing a considerable 

 number of marine shells, such as are now living in the adjacent 

 sea. I observed the deposit, which is horizontally stratified, only 

 to an elevation of 10 feet above sea-level. This surface was 

 defined by M. Purves as a terrace of ' Horizontal Marls,' a feature 

 of which, noticed by him, should not be passed over. In the upper 

 portion of the accumulation he found a considerable number of 

 land-shells, which had been washed down into the basins where 

 the marls were formed. Among these shells he found Heli.v 

 formosa, Ferussac, to be the most abundant, but the shell no longer 

 lives in this portion of the island, although it still survives in the 

 mountain district of the south-western part of the island. He also 

 found Helicina Crosby i, Nob. now extinct, and known nowhere in the 

 West Indies ; and Succinea Boonii, Nob., a species no longer living. 

 On account of these wholly or locally extinct species, although 

 commingled with a number of living forms, he concluded that 

 a considerable time has elapsed since the deposition of the beds 

 containing them. 



XI. CoPvAL-Eeefs. 



Coral-reefs are extensively developed round both the islands of 

 Antigua and Barbuda, rising to the surface of the sea, but they 

 do not appear to form elevated reefs, characterizing the margin 

 of the island. Even the low peninsulas and islands separating 

 the bays on the north-eastern coast are composed of older forma- 

 tions, but the reefs in part obstruct the entrances of the bays or 

 form ' keys ' in them. 



XII. Notes on Basbuda. 



Before considering the erosion-feat \ s of Antigua, a word may 

 be said with reference to Barbuda, which was involved in the 

 denudation of the region. This island, nearly as large as Antigua, 

 is a low undulating plain, passing into lagoons on its western side. 

 The greatest elevation is only 115 feet. While I did not visit 

 the island, Mr. Watt informed me that it was everywhere com- 

 posed of a limestone, poorly covered with soil, and he kindly gave 

 me fragments of the rock containing casts of old fossil shells, the 

 whole apparently identical with the White Limestones of Antigua. 

 This resemblance was also noticed by M. Purves. The collection 

 of Nugent contained specimens from Barbuda, among which was 

 Cyphastrcea costata, Duncan, a form of coral occurring in the 

 older Tertiary beds of Santo Domingo and Jamaica. Although the 

 evidence of the identity of the rocks in the two islands is incomplete, 

 yet there can hardly be any doubt of it, especially as they are not 

 distantly separated, and the beds of the one island lie almost along 

 the continuation of the strike of the strata in the other, but they 

 may represent higher beds of the same series preserved from erosion. 

 The recent formations, at most forming thin mantles, have not been 

 studied. M. Purves states that the land-shells are identical with 

 those of Antigua, except one variety of Helicina, thus indicating a 

 late connection of the two islands. 



