On Guano. 



315 



many years ; and hence the ravines are filled with detritus, and 

 the mountain-sides covered by piles of fine white sand, even a 

 thousand feet high." * 



It is the dryness of the climate then which has permitted the 

 guano to accumulate on these coasts. When we reach a region 

 in which from local causes the dews are heavier and the rains 

 more frequent, the accumulation ceases. Cold water, we have 

 seen, dissolves at least three-fifths of the guano in the state in 

 which it reaches us. A single day of English rain would dissolve 

 out and carry into the sea a considerable portion of one of the 

 largest accumulations ; a single year of English weather would 

 cause many of them entirely to disappear. 



When the recent guano falls it gradually dries and undergoes 

 a partial decomposition. When it is again moistened by an un- 

 usual dew, or by an accession of spray driven by the wind, it 

 again suffers a further partial decomposition, till at length it has 

 given off, as the ancient red guano appears to have done, from 

 five-sixths to nine-tenths of all the organic matter it originally 

 contained. Mr. Winterfeldt states that this ancient guano is 

 found buried beneath layers of sand ; and Iquique is mentioned 

 as one of the spots where the guano occurs. At this place^ 

 according to Mr. Darwin, the drift-sand climbs up the mountain- 

 sides in great piles to the height of even a thousand feet. This, 

 doubtless, is the sand beneath which the old droppings of the sea- 

 fowl have been gradually buried ; and to this ancient superficial 

 covering it may be owing, that the buried masses still retain so 

 much of their original organic matter. Even in that dry climate 

 the time would at length arrive when the guano, long exposed to 

 the agency of atmospheric causes, would retain only its earthy 

 and non-volatile saline ingredients. 



§ 7. Of the Economical or Money Value of Guano to the English 



Agriculturist. 



We come now to consider perhaps the most important question 

 of all, namely, the probable economical value of guano to the 

 English agriculturist. 



It may by most persons be considered impossible to arrive at 

 any satisfactory conclusions in regard to this point except by actual 

 experiment — by the trial, that is, of its precise effects on different 

 crops and in different soils. This is no doubt the m-ost certain 

 and unexceptionable method of determining its value — but this 

 method requires time, and the concurrence of many individuals. 

 Until these trials are actually made, therefore, we are entitled to 



* Researches in Geology and Natural History, p. 442. 



