488 A NATURAL BREAKWATER, [chap. xxi. 



both are nourished by putrid exhalations ; the one speaks 

 of death past, and the other too often of death to come. 



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.* 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 waveij 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 consolidated by the 

 percolation of calcareous matter, and afterwards 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, turpid with 

 sediment, are driven against the steep outside edges of this 

 wall of stone, yet the oldest pilots knew 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 SerpulcB^ together with some few barnacles and 

 nulliporae. These nulliporae, 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 the true corals, during the 

 outward growth of the mass, become killed by exposure 

 to the sun and air. These insignificant organic beings, 

 especially the SerpulcB, have done good service to the people 

 of Pernambuco ; for without their protective aid the bar of 

 sandstone would inevitably have been long ago worn away, 

 and wilhbut the bar, there would have been no harbour. 



On the 19th of August we finally left the shores of Brazil. 

 I thank God, I shall never again visit a slave country. To 

 this day, if I hear a distant scream, it recalls with painful 



* I have described this Bar in detail, in the Landon and Edinburgh Fhilo- 

 ioj'hic at Magazine, vol. xix. (1841), p. 257. 



