I83S-] DECOMPOSING SHELLS. 269 



on fragments of the underlying sandstone, and are covered by a few 

 inches thick of detritus. The shells, higher up on this terrace, could be 

 traced scaling off in flakes, and falling into an impalpable powder ; and 

 on an upper terrace, at the height of 170 feet, and likewise at some 

 considerably higher points, I found a layer of saline powder of exactly 

 similar appearance, and lying in the same relative position. I have no 

 doubt that this upper layer originally existed as a bed of shells, like that 

 on the eighty-five-feet ledge ; but it does not now contain even a trace 

 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 decomposed shells in the lower parts are associ- 

 ated 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 country 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 cottcn 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 floor of round stones. It seems, therefore, most 

 probable that at a period when the laud stood at a lower level, there was a 

 plain very similar to that now surrounding Callao, which being pro- 

 tected by a shingle beach, is raised but very little above the level of 

 the sea. On this plain, with its underlying red-clay beds, I imagine 

 that the Indians manufactured their earthen vessels ; and that, during 

 some violent earthquake, the sea broke over the beach, and converted 

 the plain into a temporary lake, as happened round Callao in 1713 and 



