Dr. Nugent on the Geology of the Island of Antigua. 465 
of coarse chert, the situation and extent of which I have endeavoured 
to trace on the map. It breaks into sharp angular blocks, which 
become strewed over the plains, as may be seen at Constitution-hill 
and Government-ground ; it is an exceedingly hard opake rock of 
various colours, with a glossy appearance on the outside of the 
broken masses, not always conchoidal, but often splintery in the 
fracture ;* containing a prodigious quantity of casts of shells, chiefly 
of the genus Cerithium, the small cavities of which are filled with 
transparent quartz or calcedony : it is nearly impossible to find a 
bit of this rock without such traces of the Cerithium. In the neigh- 
bourhood of Constitution-hill, I have met with traces of only two or 
three other minute shells ; and, as far as I can judge, they are 
Helices, or of a terrestrial or fluviatile nature. All these shells are 
more particularly seen in the rents or external surface of the stone, 
and are frequently in beautiful relief on the outside of a specimen. 
At the Church-hill in St. John’s, which stands on a patch of chert, 
with marl enveloping it, there are beautiful casts in flint of ramose 
Madreporites, Conchs, Cockles, and other shells, both univalve and 
bivalve, but the flint at this place is always opake. The lower parts 
of these chert or petrosilex beds contain likewise a most astonishing 
quantity of petrified wood ; the fragments cover the roads and plains 
for miles ; being partly derived from this chert, and partly from a 
most singular class of rocks which comes next to be described. 
There are many traces of oxyd of iron about this petrosilex; and in 
some places, Bayer Otto’s for instance, there is found a reddish 
brown earth, making not a bad pigment and water-colour, like raw 
Sienna. It may perhaps be doubted, on a casual inspection, whether 
* The fragments of this chert only want to be rounded by .attrition to resemble 
exceedingly the Kensington gravel, and sometimes are not unlike the Egyptian and other 
jaspers in pattern, as well as blood-stone in which the red colour predominates. 
3 n 2 
