NITROGENIZED PHOSPHATIC MANUEES. 



281 



Thus, leaving out of account the superficial lamellary layer which 

 obviously contains the most recently formed guano, a layer the 

 stratifications of which may be compared to the annual rings formed 

 in the trunk of a tree, three superimposed layers may be distinguished 

 in the deposit — the superficial brown layer, the middle yellow layer, 

 and the lower brown layer. The richest guano is that of the 

 middle layer. That of the upper and lower beds is the poorest. 

 This fact is easily explained by considering the incessant phenomena 

 incidental to the formation of these kind of deposits. 



TABLE LXXXI.— ANALYSES OF PEEUYIAN GUANO. 



TABLE LXXXIL— ANALYSES OF PEEUVIAN GUANO. 



Although rain is very rare in these countries, the surface of the 

 deposit is none the less moistened in a more or less constant 

 manner by the mists and fogs of winter. Now, moisture by its 



