THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



OCTOBER 1841. 



XXXVII. On a remarkable Bar of Sandstone off Pernam- 

 buco, on the Coast of Brazil. By C. Darwin, Esq., M.A., 

 F.R. # G.S.* 

 IN entering the harbour of Pernambuco, a vessel passes 

 •*■ close round the point of a long reef, which, viewed at high 

 water when the waves break heavily over it, would naturally 

 be thought to b*rof coral-formation, but when beheld at low 

 water it might be mistaken for an artificial breakwater, erected 

 by cyclopean workmen. At low tide it shows itself as a smooth 

 level-topped ridge, from thirty to sixty yards in width, with 

 even sides, and extending in a perfectly straight line, for 

 several miles, parallel to the shore. Off the town it includes 

 a shallow lagoon or channel about half a mile in width, which 

 further south decreases to scarcely more than a hundred yards. 

 Close within the northern point ships lie moored alongside 

 the reef to old guns let into it. 



Transverse section : vertical heights considerably exaggerated. 

 A. Level of the sea at low water. 

 D. Subsided masses, thickly coated with Serpulae, &c. 



f Summit of the bar, which generally slopes a little seaward ; but 

 the slope in the woodcut has been unintentionally somewhat 

 increased. 



D. Subsided masses of bare sandstone. 



E. Surface of the harbour or lagoon. 



* Communicated by the Author. 

 Phil, Mag. S. 3. Vol. 19. No. 124. Oct. 1841. S 



