XXI 
SINGULAR REEF 
529 
The most curious object which I saw in this neighbour¬ 
hood was the reef that forms the harbour. I doubt whether in 
the whole world any other natural structure has so artificial an 
appearance. 1 It runs for a length of several miles in an 
absolutely straight line, parallel to and not far distant from 
the shore. It varies in width from thirty to sixty yards, and 
its surface is level and smooth ; it is composed of obscurely- 
stratified hard sandstone. At high water the waves break 
over it; at low water its summit is left dry, and it might then 
be mistaken for a breakwater erected by Cyclopean workmen. 
On this coast the currents of the sea tend to throw up in front 
of the land long spits and bars of loose sand, and on one of 
these part of the town of Pernambuco stands. In former 
times a long spit of this nature seems to have become con¬ 
solidated by the percolation of calcareous matter, and after¬ 
wards to have been gradually upheaved ; the outer and loose 
parts during this process having been worn away by the action 
of the sea, and the solid nucleus left as we now see it. 
Although night and day the waves of the open Atlantic, turbid 
with sediment, are driven against the steep outside edges of 
this wall of stone, yet the oldest pilots know of no tradition of 
any change in its appearance. This durability is much the 
most curious fact in its history ; it is due to a tough layer, a 
few inches thick, of calcareous matter, wholly formed by the 
successive growth and death of the small shells of Serpulse, 
together with some few barnacles and nulliporse. These 
nulliporse, which are hard, very simply-organised sea-plants, 
play an analogous and important part in protecting the upper 
surfaces of coral-reefs, behind and within the breakers, where 
1 I have described this Bar in detail in the Loud, and Edin. Phil. Mag. vol. 
xix. (1841), p. 257. 
2 M 
