Vol. 67.] OF ANTIGUA AND OTHER WEST INDIAN ISLANDS. 687 



quelles deposent en se refroidissant en vastes nappes de roclies aflectant la 

 texture du silex et de la calccdoine.' (Bull. Mus. Roy. Hist. Nat. JJelg. 

 vol. iii, 1884-85, p. 300.) 



.Both Purves and Spencer in the diagrams given in their papers 

 have represented the ' stratified tuffs,' that is the formations of 

 the ' Central Plain,' as passing under the Calcareous or Antigua 

 Formation, which is thus made to overlie these tuffs. But this is 

 purely hypothetical, and I do not think that it is home out by the 

 evidence. I doubt whether the contact between these formations 

 is anywhere observable. It is much more probable that the tuffs 

 abut against the upraised edges of the calcareous beds, but any 

 such junction is hidden by the tuffs and volcanic debris of the 

 ' Central Plain.' It is likely that the volcanic formations of 

 the tuffs, and the marine and freshwater cherts, etc., are younger 

 than the calcareous beds of the Antigua Formation. The specimen 

 of Orbitoides said to have been found in the chert may easily have 

 been derived from the adjoining calcareous rocks of older date. 

 And, although the fossil corals of Antigua were considered by 

 Duncan to have generally preponderating Miocene affinities, there 

 is no certainty on this point. Many of them, indeed, came from 

 the chert, and his ideas regarding the geology of the island, based 

 on the information supplied by Nugent, are entirely supplanted by 

 Purves's observations. 1 



The Antigua Formation is of a very Cretaceous aspect, containing 

 Orbitoides in vast numbers and of a high degree of development, 

 and its other organic remains are not inconsistent with the theory 

 of a late Cretaceous age for it. A circumstance that might induce 

 one to pause before regarding the formation of the ' Central Plain ' 

 as more ancient than the Antigua Formation, is the extremely 

 modern aspect of the fauna of the freshwater chert as enumerated 

 by Purves. Even though some of the species are said not to be now 

 living in Antigua, yet it is doubtful whether they can be distin- 

 guished from West Indian living forms. The list of fossils comprises 

 four freshwater shells, two terrestrial shells, and two so-called 

 amphibious shells. The last-named, Melampus and Truncatella, are 

 never found in the water, and only within reach of the salt spray and 

 in sheltered places. Melampus lives in the crevices of rocks above 

 high- water mark ; Truncatella lives on the ground above high -water 

 mark, among pebbles and weeds. These molluscs cannot live in 

 water, and they, as well as the other mollusca, were no doubt 

 drowned in the hot siliceous waters of the Central Plain — hence the 

 preservation of the soft parts in the shape of silicified casts, as 

 described by Purves. The identification of the shell ascribed to 

 Pomatias is uncertain ; it is more likely a Tudora or a Cistula, such as 

 now inhabit Anguilla and the neighbouring islands. As regards the 

 Nematura, which is another case of uncertainty, for it is admitted 

 that it might be an Amnicola (a genus common in all the West- 

 Indian islands), it would be nothing extraordinary, even were it 

 rightly identified, for Ave have Helix labyrinthica at the same time 



1 P. M. Duncan, Q. J. G. S. vol. xix (1863) p. 410. 



