THE VOYAGE OF THE BEAGLE 391 



trace of organic structure. The powder has been analyzed 

 for me by Mr. T. Reeks; it consists of sulphates and muri- 

 ates both of lime and soda, with very little carbonate of 

 lime. It is known that common salt and carbonate of lime 

 left in a mass for some time together, partly decompose each 

 other; though this does not happen with small quantities in 

 solution. As the half-decomposed shells in the lower parts 

 are associated with much common salt, together with some 

 of the saline substances composing the upper saline layer, 

 and as these shells are corroded and decayed in a remarkable 

 manner, I strongly suspect that this double decomposition 

 has here taken place. The resultant salts, however, ought 

 to be carbonate of soda and muriate of lime; the latter is 

 present, but not the carbonate of soda. Hence I am led to 

 imagine that by some unexplained means, the carbonate of 

 soda becomes changed into the sulphate. It is obvious that 

 the saline layer could not have been preserved in any coun- 

 try in which abundant rain occasionally fell: on the other 

 hand, this very circumstance, which at first sight appears so 

 highly favourable to the long preservation of exposed shells, 

 has probably been the indirect means, through the common 

 salt not having been washed away, of their decomposition 

 and early decay. 



I was much interested by finding on the terrace, at the 

 height of eighty-five feet, embedded amidst the shells and 

 much sea-drifted rubbish, some bits of cotton thread, plaited 

 rush, and the head of a stalk of Indian corn: I compared 

 these relics with similar ones taken out of the Huacas, or old 

 Peruvian tombs, and found them identical in appearance. 

 On the mainland in front of San Lorenzo, near Bellavista, 

 there is an extensive and level plain about a hundred feet 

 high, of which the lower part is formed of alternating layers 

 of sand and impure clay, together with some gravel, and the 

 surface, to the depth of from three to six feet, of a reddish 

 loam, containing a few scattered sea-shells and numerous 

 small fragments of coarse red earthenware, more abundant 

 at certain spots than at others. At first I was inclined to 

 believe that this superficial bed, from its wide extent and 

 smoothness, must have been deposited beneath the sea; but 

 I afterwards found in one spot, that it lay on an artificial 



