72 : Geology of St Crorw. ei . 
few more delicate shells of the genera Serpula, Lucina, Voluta; 
Bulla, &e.; all these species still inhabit the surrounding seas. 
In addition to this fact, there are other circumstances which show 
the recent origin of this deposit. This part of the coast is liable 
to a strong surf, which is constantly drifting shells and other sub- 
“stances upon the shore, and dashing ever them spray charged 
— vith calcareous matter. These generally unite and harden, espe- 
~~ eially near the surface, and form into a tolerably compact mass. 
“as found imbedded in these rocks, iron utensils, which had 
been employed at no very remote period, in quarrying them. It 
contains many fragments and rounded pebbles of indurated clay, 
which as a general thing unfit it for the kiln. 
Though it is obvious these rocks are still in the process of for- 
mation, they have been much abraded and broken by the surf. — 
I doubted, indeed, for some time, whether they could have been 
formed in the face of such powerfully abrading agents 5 but the ; 
fact, that the windward coasts of coral islands are generally d 
tinguished by the greatest accumulations of matter, rer 
difficulty. I saw in one place a mass of rock containing abe 
hundred cubic feet, which had been detached from its bed, 
several feet, and thrown back upon the shore. This deposit every 
where rests upon the tilted strata of the indurated clay, which 
often form a precipitous bank, and generally rise within a short 
into high mountains. The shore is lined with tropical 
shrubs and trees, such as ‘Hippomane mancinella, Guilandina 
bonducella, Coccoloba uvifera, Lantana involucrata, Turnara ul- 
mifolia, Mimosa spinosa, &c. 
The marl varies in composition, and hardens even ‘wiibin mod- 
rate distances. It often comprises extensive beds of lime nearly 
pure, and so soft that it may be dug with a hoe ; in other places, 
it is mingled with sand, becomes harder, and forms a good build- 
ing stone. In such cases, it is easily broken at first, but hardens 
by exposure to the atmosphere. In structure and general aspect 
1 saw quarries much resembling those of the Paris basin, from 
which such ample materials for building are derived. 
-It is impossible to draw a dividing line between these beds and 
the purer lime deposits on the south and west. Both. are no 
doubt contemporaneous, and owe their difference to peculiar cil 
Pg their deposition. The limestone sometimes occurs 
in a compac 3 but.the structure is generally loose and fnia- 
“ 
