314 



On Guano. 



equally of England and of America, seems to depend upon two 

 circumstances — 1st, on its containing a well -tempered mixture 

 of a great number of those substances which the plant requires for 

 its perfect growth and development ; and — 2nd, on this admix- 

 ture including a considerable proportion of a substance (ammo- 

 nia) which in a remarkable degree hastens the growth of the 

 young plant, as well as of another (phosphate of lime) which is 

 necessary to its healthy and perfect maturity. 



In the arid plains of Peru, where dews are rare and rain 

 scarcely ever falls, we can easily appreciate the value of a sub- 

 stance which shall make the young plant as it were rush up when 

 a favourable day of moisture comes, shall facilitate its rapid 

 after-growth, and shall supply the materials necessary to its perfect 

 maturity ere the burning sun and parching winds have time to 

 scorch and wither it. Useful as it is likely to prove in our 

 climate, therefore, the beneficial effects of guano may never be so 

 striking in these latitudes as they have long appeared on the shores 

 of Peru. 



§ 6. The Cause of its Accumulation on the Coast of Peru. 



Connected with this last observation is the explanation of the 

 accumulation of the guano on the coast of Peru. I have already 

 stated that, according to Humboldt, it is met with only between the 

 13th and 21st degrees of south latitude, though the sea-fowl are 

 equally plentiful both to the north and to the south of these 

 parallels. The explanation of this apparent anomaly is to be 

 found in the climate of this part of South America. 



Nearly the whole of the land along this coast, between the 

 Cordilleras and the sea, is one continued desert. *' I have al- 

 ways," says Mr. Darwin,* applied the terms barren and sterile 

 to the plains of Patagonia, yet the vegetation there can boast of 

 spiny bushes and some tufts of grass, which is absolute fertility 

 to anything that can be seen here" (the neighbourhood of Copiapd). 



In Peru real deserts occur over wide tracts of country." It 

 has almost become a proverb that rain never falls in the lower 

 part of Peru." " That much rain does not fall is very certain, 

 for the houses are covered only with flat roofs made of hardened 

 mud ; and on the mole (at Callao) ship-loads of wheat were 

 piled up, and are thus left for weeks without any shelter. "f 



The town of Iquique contains about 1000 inhabitants, and 

 stands on a little plain of sand at the foot of a great wall of rock 

 2000 feet in height, which here forms the coast : the whole is 

 utterly desert. A light shower of rain falls only once in very 



* Researches in Geology and Natural Historv, p. 428. 

 t Ibid., p. 446. 



