Geology of Antigua. 79 
pula, pecten, cardium, strombus, cerithium, ostrea, trochus, cy- 
prea, turritella, venus, lucina,” &c. ese are sometimes found 
entire, but they generally occur in the form of casts, either calea- 
reous or silicious. Dr. Nugent also mentions several species of 
land and fluviatile shells, belonging principally to the genus He- 
lix, which he has observed associated in the same locality with 
marine genera, as murex, arca, nerita, purpura, chama, trochus, 
c. The most of these fossils have ving exemplars in the sur- 
rounding seas. From the specimens which came in my way, 
(for I did not see a complete collection, ) I think I should be safe 
in estimating the proportion of such as high as 70 per cent. 
If this estimate be taken as an approximation to the truth, the 
formation must belong to the latest tertiary or newer Pliocene pe- 
riod of Lyell. No relics. of mammalia have yet been discovered 
in this group, nor indeed in any upon the island.* 
As to the age of the clay formation, I have not sufficient data 
to form an opinion. With the exception of some petrified leaves 
found near its junction with trap at Drew’s Hill, I could not as- 
certain that any organic remains had been discovered in it. 
These leaves belong to trees of the dicotyledonous class. Dr. 
Nicholson thinks he recognizes among them those of the Ficus 
pertusa, and a species of Melastoma. The mineralogical charac- 
ter of these rocks certainly does not indicate great age ; still, 
neither this nor any thing in their relations to other rocks, points 
out their absolute place in the series of geological formations. 
We must wait, therefore, for farther light on this point, till their 
organic contents are better investigated. 
Intimately connected with the clay. fortnation, if not constitu- 
ting.a part of it, is another class of rocks of a most interesting 
character. . I ‘cabs ‘to the extensive beds of chert and the silici- 
ous petrifactions with which this. part of the island abounds. 
Dr. Nugent describes these beds as a distinct deposit, lying above 
the clay and below the marl.. His opinion is probably well found- 
ed ; but they are so intimately associated with the clay formation, 
that I prefer to class them with that group. Their comparative 
extent is not great. They are found principally in the neighbor- 
_ Of the age of the corresponding formation in Barbadoes I can speak with 
greater- certainty. Of forty one species of conchifera and mollusca, which I ob- 
tained during ten days’ residence upon the island, there were only three which are 
not found at present in a living state in the West Indies, 
