234 ANNUAL OF SCIENTIFIC DISCOVEKY. 



Numerous analyses shortly modified this opinion as too positive. The 

 sagacious Schiibler even sought to prove, in a research that has be- 

 come classic, that the fertility of a soil depends more upon its physical 

 properties, its state of aggregation, power of absorption, etc., than 

 upon its chemical constitution. 



" The physical properties, in my opinion, do not enable us, more 

 than the chemical composition, to pronounce upon the degree of fer- 

 tility of the soil. To decide this point with some measure of certainty, 

 it is indispensable to have recourse to direct observation ; it is neces- 

 sary to cultivate a plant in the soil, and ascertain with what vigor it 

 develops there ; the analysis of the plant afterward intervenes use- 

 fully, to indicate the kind and quantity of the elements that have 

 been assimilated." 



There has been much progress made in our knowledge of the soil 

 during the last ten years. This advance has not consisted in reveal- 

 ing to us the presence of new elements, lithia perhaps excepted, 

 nor in fixing with any more certainty the quantitative limits which 

 separate barrenness from fertility ; it has not shown what is the com- 

 position of a silurian or a sub-carboniferous, a drift, or a tertiary soil ; 

 it has not defined the soil adapted to wheat, or that productive of 

 clover ; it has not indicated the manures which this or that soil 

 needs ; but, content with the fact that all soils which naturally sup- 

 port vegetation contain the elements of vegetation, it has sought 

 to ascertain in what forms these elements are assimilable, how they 

 may be made available, what changes or reactions in the soil aifect 

 its productiveness, how fertilizers act indirectly (their influence 

 often having no relation to any supposable direct action), how the 

 soil affects the life of the plant otherwise than by feeding it, etc. etc. 



"We are approaching, in fact, by slow degrees, to an understanding 

 of the physiological significance of the soil, a grand result to which 

 chemistry and physics cooperate. 



GUANO. 



We derive the following items respecting this important manure 

 from an interesting paper recently presented to the French Academy 

 of Sciences by M. Boussingault. The deposits of guano (liuano de 

 pajoro) extend from the 2d to the 21st degree south latitude along 

 the coast of Peru. Those which lie beyond these limits are much 

 poorer in ammoniacal compounds than the former, and are not, 

 therefore, equal to them in value. Guano is generally found depos- 

 ited on small promontories or on cliffs ; it fills up crevices, and is in 

 general to be found in those places where the birds seek shelter. 

 The rocks of this part of the coast consist of granite, gneiss, syenite, 

 and porphyritic syenite ; the guano which covers them generally exists 

 in horizontal layers ; but sometimes the latter have a strong inclina- 

 tion, as at Chipana, for instance, where they are nearly vertical. 

 The guano deposits are generally covered with an agglomeration 

 of sand and saline substance, called ealiche, which the laborers first 

 remove before they begin their attacks on the guano. In some 

 places, as at Pabellon de Pica and at Punta Grande, the deposits lie 

 under a mass of sand descending from the neighboring mountain ; and 



