404 APPENDIX H. 



without a considerable reduction of produce ■• — a fact which 

 sufficiently refutes the old mistaken notion of the inexhaustible 

 fertility of the soil in the tropics. 



On the western coast of Peru only those parts are extremely 

 sterile, where no little artificial canals convey to the dry soil the 

 water from the torrents of the Andes, which carries with it the 

 mineral detritus washed from the declivities of the mountains. 

 Wherever such artificial canals exist, and the conditions of the 

 ground are favourable, the soil on the coast as well as in the 

 interior .of Peru and Bolivia is almost as productive as in the 

 interior of the highlands of Ecuador, New Grranada, and Guate- 

 mala. But it is not the water which is the agent in maintaining 

 the steady productiveness of the soil, but, as in the case of 

 the Delta of the Nile in Egypt, it is the mud carried along 

 with the water, and which has been washed away from the dis- 

 integrated rocks of the Andes. The constituents of this mineral 

 detritus, which are partly contained in the water in a state of 

 minute mechanical division, and partly held in chemical solu- 

 tion, are brought to the fields by small channels. The water 

 thus conveyed from the mountains in innumerable furrows is 

 soon absorbed by the soil or evaporated, leaving a rich fertilising 

 deposit behind. Pure rain water would be of very little avail, 

 as, for instance, in the extensive tableland of Tacungar, with its 

 barren pumice stone fields, where quite near the equator rain 

 pours down almost daily during nine months of the year. It is 

 not the atmospheric water that acts as the fertilising agent, but 

 the muddy streamlets from the Andes. In Peru the fertilising 

 action of guano is more enduring than in England, because the 

 potash which the guano does not restore to the soil, is there 

 supplied in the detritus from the trachytic constituents of the 

 Andes ridge, which abound in felspar. This natural mineral 

 manure is of the same high value in the South American lands 

 of the Andes chain as the fertile Loss, accumulated by the great 

 flood in past ages at the foot of the Bavarian and Swiss Alps. 

 It is a fact full of meaning that the inhabitants of those parts 

 of America should have arrived at the same simple means of 

 restoring to the land the mineral constituents carried away by 

 the crops, which are at the present day generally resorted to 

 also under similar favourable conditions of the ground in the 



