xxiv INTRODUCTORY CHAPTER. 



A species of natural cement is found on several parts of the coast 

 of St. Helena, which seems to resemble that seen by M. Peron* 

 on the coasts of the isles of Kangaroos, St. Peter, and St. Francis. 

 This writer ascribes its formation, at these places, to numerous 

 shells rolled incessantly by the action of the waves on the neigh- 

 bouring shores ; which being broken into very minute fragments, 

 and mixed with cjuartzose sand, speedily constitute the principle of 

 calcareous cement of a superior quality. The finest specimen I 

 observed at St. Helena, is between Egg Island and Union Cove. 

 The rocks bear evident marks of the action of fire. They resemble 

 the refuse of iron at smelting places. There are also numerous 

 pumice stones, and a sort of shingle scattered over the surface of 

 these rocks. Some very hard stones are so firmly bedded in this 

 cement, that, in attempting to take them out, they broke in pieces. 

 If such a cement could artificially be made, it would undoubtedly 

 be far superior to the Roman, or any other cement hitherto 

 invented. 



It seems to me that a likely mode of ascertaining the process 

 of formation would be to imitate that which appears to have 

 been the process of nature ; that is, to collect a certain quantity of 

 powdered St. Helena limestone, to mix it with small fragments of 

 basaltic stone, the size of coarse sand, varying the proportions ; 

 then to sprinkle the mixtures occasionally with sea water, and leave 

 them to dry in the sun. If these ingredients should not consolidate 

 at first, the sprinkling of sea water should be continued ; and pos- 

 sibly in the course of time, the consolidation might take place. 

 This appears to have been the process of nature ; for the natural 

 cement bears an exact resemblance to mortar made with white 

 lime, and an admixture of coarse black sand : but, as there is no 

 sand on the coast, nor in the interior of the island, it may be 



• Jour, de Phys. Vol. LIX. 



