sriALEB.] INTRODUCTION. 17 
especially in the section from Virginia southward; in the Archaean dis- 
trict of Missouri and Arkansas, and in the vast region of highly meta- 
morpbic rocks of the Cordilleran district, extending from the Rocky 
Mountains to the Pacific Ocean. It is true that at present the economic 
value of phosphatic deposits in the western part of the continent would 
probably be small, on account of the great cost of transportation to the 
seaboard districts; but the growing use of phosphatic manures in the 
Mississippi Valley and the rapid exhaustion of the soils of that dis- 
trict will soon give commercial importance to any sources of supply of 
phosphates that may be found in any parts of the Cordilleras which 
are convenient to transportation. 
A proper study of the mineral manures of this country can best be 
carried on by means of a well considered co operation between geolog- 
ical explorers and the experiment stations of the several States. At 
present the methods of using mineral phosphates are extremely costly: 
not only is the material brought into the soluble condition by satura- 
tion in sulphuric acid, but it is then mingled with ammoniacal and other 
matter to increase its effect as a fertilizer. The result is that, although 
a ton of Carolina phosphate now costs bat $(>, the average price of the 
manufactured product to the consumer at the phosphate factories is 
about $30 per ton. It is probable that the essential value of the phos- 
phatic ingredients to the plants of most soils is not enhanced by this 
costly treatment, though an incidental but dearly purchased gain, in the 
case of some crops, is obtained from the ammoniacal matter. The only 
effect of the superphosphatizing on the phosphatic matter is to make it 
more immediately absorbable by the plants. If placed on the soil with- 
out any other preparation than grinding, lime phosphate will slowly 
pass into a condition in which it may be absorbed by plants, while if 
treated with sulphuric acid it is for a time at least in a soluble state. 
That this treatment is not essential is well shown by the fact that the 
phosphatic matter derived from the rocks is brought into a condition 
for absorption by the ordinary process of decay in soils. Our present 
costly method of applying phosphates has come about through the 
commercial history of artificial manures, which is as follows: 
Before guanos were brought into use the English farmers had learned 
that they could profitably use the phosphatic marls of their Tertiary and 
Cretaceous deposits without any artificial preparation. If guanos had 
not existed it seems likely that mineral phosphates would have always 
been used in this way. When the Peruvian guanos came into use 
they afforded a much more stimulating material than any other pur- 
chasable manures, and in a short time they established the type of com- 
mercial fertilizers. When the sources of supply of these guanos be- 
came in part exhausted, artificial compounds, formed on a basis of rock 
phosphates or apatites, were devised to take their place. These were made 
to imitate the effect of the guanos as closely as possible. Like them, they 
Bull. 40 2 (491) 
