32 



same white marl which crops out at the surface in Colonia A, at the edge 

 cf the swamp and at some distance from the field under investigation. 

 The agricultural analyses of these soils have been given on previous pages 

 of this bulletin. We have seen that the black material is very rich in 

 humus, and that even the marl underneath to the depth of two two feet 

 is well supplied with it. In accordance with this the nitrogen content of 

 the black material is very high, exceeding two per cent of the dry soil, 

 decreasing in the lower layers. The subsoil consists of almost pure calcium 

 carbonate, and even the black material contains on the average 8.65% of 

 lime. The magnesia is .8% in the soil and 1.75% in the subsoil. Potash 

 and phosphoric acid are low, .2 and .1% respectively in the soil, and .065 

 and .02% in the subsoil. 



If we now compare the nature of the injurious soil constituents 

 existing in the first series of soils with that of those contained in this 

 series, we find some very remarkable and important differences. 

 Generally speaking, the soils used in the first investigation are very 

 different in character from those which we are to discuss now. All samples 

 but one of the first series were collected within a radius of 2,800 meters 

 from the central factory and represented regular mineral soil types. In 

 the present series, however, we have to deal with vegetable moulds, formed 

 in a medium impregnated with salts. In the first as well as in the second 

 area we find white incrustations on the surface of the land, but in their 

 composition the incrustations from the two places are entirely different. 

 In the first area the crust was found to consist mainly of sodium chloride, 

 with small amounts of the sulfates and bicarbonates of calcium 

 magnesium and potassium. The incrustation that is found in enormous 

 quantities in the swamp area of the Cano de Tiburones, on the other 

 hand, is for the most part insoluble in water and consists principally of 

 calcium carbonate. The water soluble part of this incrustation amounts 

 to less than one half per cent of the total, and is made up of about equal 

 parts of bicarbonates, chlorides and sulfates. The analyses of this 

 incrustation follow here : 



COMPLETE ANALYSIS 



Moisture 2.50% 



Insoluble i esidue 0.78% 



Carbon dioxide and volatile matter 45.79% 



Iron oxide and alumina 0.94% 



Lime 48.37% 



Magnesia 1.23% 



Potash .... 0.04% 



Soda 0.18% 



99.83% 



