NATURE AND ORIGIN OF DEPOSITS OF PHOSPHATE OF LIME. 
By R. A. F. Penrose, Jr. • 
IMPORTANCE OF PHOSPHATE OF LIME IN NATURE. 
Phosphorus is one of the most universally distributed of all the ele- 
ments. It is found in all animal and vegetable matter, as well as in 
most eruptive and sedimentary rocks. Phosphoric acid composes over 
40 per cent, of the ashes of bones and in the vegetable kingdom it is 
especially abundant in the seeds of plants. Thus the ash of wheat con- 
tains over 49 per cent, of phosphoric acid. 
It has been estimated that for each cow kept on a pasture through 
the summer there are carried off, in veal, butter and cheese, not less 
than fifty pounds of phosphate of lime. Consequently it will be seen 
that phosphoric acid is one of the most important elements of plant 
food, and no soil can be productive which is destitute of it. The neces- 
sity of restoring phosphoric acid to an exhausted soil has been ac- 
knowledged from very ancient times, though the cause of its stimulat- 
ing effect was unknown until a comparatively late date. In the days of 
the Romans the excrements of birds, from pigeon-houses and bird-cages, 
brought a high price, and Edrisi relates that the Arabians, as early as 
1154 A. D., used the guano deposits found along their coast for agri- 
cultural purposes. Garcilaso de la Yega (Oomentarios Reales, lib. V, 
1604) says that the Peruvians, in the twelfth century, used the guano 
beds on their islands as fertilizers. Of such importance did they esteem 
the material of these beds that the penalty of death was imposed by the 
early Incas on any one found killing the birds that made these precious 
deposits. It was not, however, until the early part of this century, when 
Liebig and others showed the important part played by phosphoric acid 
in vegetable life, that artificial phosphatic manures came into use, and 
it is only in the last twenty years that the mining of natural phosphates 
with their conversion into superphosphates has assumed its present 
great and steadily increasing importance. 
CLASSIFICATION OF DEPOSITS OF PHOSPHATE OF LIME. 
The classification of deposits- of phosphate of lime is a matter attended 
with many difficulties, not only on account of the great variety of forms 
in which phosphate of lime occurs, but also because many varieties grad- 
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