370 rp:RU. [chap. XVI. 



iKxce of organic structure. The powder has been analysed for 

 me by Mr. T. Reeks ; it consists of sulphates and muriates 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-de- 

 composed shells in the lower parts are associated with much 

 common salt, togetiier with some of the saline substances com- 

 posing 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 melius, the car- 

 bonate of soda becomes changed into the sulphate. It is obvious 

 that the saline layer could not have been preserved in any 

 country in which abundant rain occasionally fell : on the other 

 hand, this very circumstance, which at first sight appears £0 

 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 d composition 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 ai)out 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 Avide extent and 

 smoothness, must have been deposited beneath the sea ; but I 

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

 round stones. It seems, therefore, most probable that at a pe- 

 riod when the land stood at a lower level, there was a plain very 



