12 



Silurian System. 



(Appearance of vertebrata ) 

 Welsh Bala beds. Berwyn Phosphate mine. 

 Lingula flags (Quebec) 40% tribasic. 

 Angers slates (France). 

 Phosphate limestone of Kentucky. 

 Logrosan (Spain) Phosphorities (Apatites ?) 

 Caceres (Spain) " 



Portugal " 



Cambrian System. 



(Appearance of Protozoa, Mollusca, Annuloida, and Crustacea.) 



Laurentian System. 

 Canadian Apatite. 

 Norwegian Apatite. 



Thus at the present time, we have Mineral phosphntes of lime in 



process of formation, and principally known in commerce as " Crust 



guano". 



Looking at the chemical composition of average Bird guano, we 



find it to be composed ot the following constituents : — 



Moisture 15.8 



Organic matter and Ammoniacal Salts 52-5 



Phosphates of lime 19.5 



Phosphates of Iron and Alumina 3.1 



Alkaline Salts 7.6 



Silica and Sand 1.5 



This typical analysis is from the average of 15 samples, made by 



Nesbit on the Chinchas Inland (juano. 



An elementary knowledge of chemistry will assist us to perceive 



what a large proportion of the above constituents will be leached out 



by water, or dissipated by prolonged exposure to ordinary atmospheric 



influences, especially when we remember that the organic matter above 



mentioned comprises uric, oxalic and phosphoric salts of alkalies and 



ammonia, and even about one third of the phosphates of lime is found 



to be soluble m water. Given a deposit of guano on a limestone soil 



or rock, and it is readily perceived that every shower will contribute to 



the steady but continual process of the transmutation of the carbonate 



of lin-e into phosphate of lime, in consequence of the discharge of the 



weaker carbonic acid, by the stronger phosphoric acid. 



