464 Dr. Nugent on the Geology of the Island of Antigua. 
marine and terrestrial or fluviatile exuviae separately exist, but the 
marl containing the two classes together is extremely common, and 
occupies a great proportion of the whole superficies of the calcareous 
formation. It is principally for the great variety and beauty of its 
siliceous and agatized fossils that this island is so remarkably distin- 
guished beyond any similar tract of country yet described ; and the 
greater proportion of them are found in the calcareous beds of which 
we are now treating. There occur in it, not only calcedonic and 
flinty casts of several bivalves and univalves, but an infinite variety 
of madrepores thus metamorphosed, with which the Society is now 
familiar, from the specimens formerly transmitted to it. Many of 
these agatised corallines appear to be of different kinds from those 
recent ones engraved in the work of Ellis. That division of the 
island called Belfast, particularly in the immediate vicinity of the 
church, contains the greatest quantity of these agatised corals ; but 
they are likewise to be met with in other parts, though generally of 
inferior beauty. In many cases the siliceous particles appear to have 
been modified by the contact of the organic substance, and present 
in different parts the appearance of opal, calcedony, or quartz, and 
being occasionally tinged with iron, and probably bitumen, exhibit 
a vast variety of transparent and beautiful agates, enriched with 
dendritic traces resembling the mocha stone, which, properly 
worked by the lapidary, make very pleasing ornaments, and far 
excel the generality of coralline agates found in other parts of the 
world, I know of no bones or other traces of larger animals in 
this formation, nor is there here found any gypsum; but the 
calcedony in minute patches of a few inches in length is often 
cellular, and not unlike the bun>stone of the French beds. 
Subordinate to the lowest beds of this calcareous formation, and 
lying on its more southern limit, we find extensive irregular masses 
