274 Decay of Upraised Sea-Shells. past n. 



On most parts of tlie second ledge or old sea-beach, 

 at a height of 170 feet, there is a layer of white powder 

 of variable thickness, as much in some parts as two 

 inches, lying on the angular, salt-cemented fragments 

 of sandstone and under about four inches of earth, which 

 powder, from its close resemblance in nature to the 

 upper and most decayed parts of the shelly mass, I can 

 hardly doubt originally existed as a bed of shells, now 

 much collapsed and quite disintegrated. I could not 

 discover with the microscope a trace of organic structure 

 in it : but its chemical constituents, accordino' to Mr. 

 Seeks, are the same as in the powder extracted from 

 amongst the decaYing shells on the lower ledge, with 

 the marked exception that the carbonate of lime is 

 present in only very small quantity. On the third and 

 highest ledge. I observed some of this powder in a 

 similar position, and likewise occasionally in small 

 patches at considerably greater heights near the summit 

 of the island. At Iquique, where the whole face of the 

 country is covered by a highly saliferous alluvium, and 

 where the climate is extremely dry, we have seen that, 

 according to Mr. Blake, the shells which are perfect 

 near the beach become, in ascending, gradually less 

 and less perfect, until scarcely a trace of their original 

 structure can be discovered. It is known that car- 

 bonate of lime and common salt left in a mass together, 1 

 and slightly moistened, partially decompose each other : 

 now we have at San Lorenzo and at Iquique, in the 

 shells and salt packed together, and occasionally mois- 



1 I am informed by Dr. Kane, through Mr. Reeks, that a manu- 

 factory was established on this principle in France, but failed from 

 the small quantity of carbonate of soda produced. Sprerjgel 

 Gardeners' Chron.' 1845, p. 157) states, that salt and carbonate of 

 lime are liable to mutual decomposition in the soil. Sir H. De la 

 Beche informs me, that calcareous rocks, washed by the spray of the 

 sea, are often corroded in a peculiar manner ; see also on this latter 

 subject ' Gardeners' Chron.' p. 675, 1841. 



