PENROSE.] GUANOS. 117 
this kind derived their phosphate of lime from the numerous animals, 
having phosphatic shells, whieh inhabited the Silurian sea. 
Phosphatic limestone beds, like those just described, supply the soil 
of the surrounding country with large quantities of phosphate of lime, 
and it is very likely that the wonderful fertility of some districts in the 
limestone regions of Kentucky and Virginia is due to the decomposition 
of such beds. 
Analysis of Fayette County phosphatic limestone, by Dr. Peter (Kentucky Geol. Sum., 1878). 
Dried at 212° F. 
Phosphoric acid, lime, magnesia, alumina, iron oxide „ 85.270 
Carbonate of lime 9. 180 
Carbonate of magnesia 371 
Silica and insoluble silicates 4.780 
Fluoride of calcium, alkalies, organic matter, etc., not estimated .399 
Total - 100.000 
GUANOS. 
The class of guanos includes all those deposits which are largely, or 
entirely, composed of the excrement of birds. Such deposits are sub- 
divided into soluble guano and leached guano. The former is composed 
of deposits which have preserved all, or a large part of, their soluble 
ingredients, while the latter includes such as have lost these soluble 
constituents by the action of rain or sea-water, and have been converted 
into a mass, insoluble, or almost insoluble, in water, and varying, in 
consistency, from a loose powder to a hard compact rock. 
The soluble guanos will be treated first, and then the leached guanos 
will be described. 
SOLUBLE GUANO. 
Most of the soluble guano of commerce has come from the coast of 
Peru. It has been used in that country for agricultural purposes from 
very ancient times. Of such value was it esteemed by the natives that 
the punishment of death was imposed by the early Incas and their 
Spanish successors on any one who was found killing the birds that 
made these precious deposits. Peruvian guano was first recommended 
(1801) to be used in the raw state for agricultural purposes in Europe 
by Humboldt, who brought a specimen from the islands off the coast of 
Peru ; but it was not exported in any considerable quantities until 1812, 
when 182 tons were shipped to England. After that time the use of it in- 
creased very rapidly until 1870-1875, when the best beds were exhausted, 
and the use of acidulated phosphates gradually drove the poorer qual- 
ities almost entirely out of the market. It is still imported to the United 
States and Europe as a source of superphosphate. In the raw state 
very little of it is used compared with the immense quantities of super- 
phosphates now sold. 
(591) 
