February 22, 1889.] 



SCIENCE. 



'47 



terial might advantageously be used in a local way for fertilizing 

 purposes. 1 



The search for phosphatic materials in the stratified rocks de- 

 mands a method of inquiry that has not yet been applied to the 

 study of our rocks. It seems to me that the method, or rather 

 methods, should be as follows : — 



First, there should be a careful inquiry to determine the share in 

 which the several important groups of rock-making organic forms 

 contribute phosphatic matter to strata. This can be accomplished 

 by carefully comparing the chemical character of particular strata 

 with the fossils the beds contain. When this determination is made, 

 we shall have one means of guiding our inquiries, which will surely 

 be of great value in the search for bedded phosphates. 



Second, we should have a carefully executed chemical survey of 

 our stratified rocks. Enough can be gathered from the scattered 

 records of chemical analysis to make it plain that certain features 

 of the chemical character of particular beds or divisions of strata 

 often extend laterally for great distances. This is shown in a gen- 

 eral way by the character of the soils formed of the waste of par- 

 ticular horizons ; for instance, the deposits of the horizon on which 

 lies the Cincinnati group of this country and the equivalent deposits 

 of Europe are nearly always well suited to grasses and grains, and 

 have a great endurance to tillage. It is now desirable to take these 

 beds which promise to afford mineral manures, and subject each 

 stratum to analyses which shall determine the quantity of phos- 

 phoric matter, soda, and potash which they contain, so that their 

 fitness for use as mineral manures may be ascertained. 



Below the level of the Silurian and Cambrian strata, and partly 

 in those sections where they have been much metamorphosed, lies 

 the field of the vein phosphates. It is more than likely that in 

 this vast thickness of rocks, with their development in this country, 

 there are many extensive sources of this class of phosphates which 

 await discovery. As yet no careful search has been made for such 

 veins in any part of the United States. The regions most likely to 

 contain such deposits are found in the central parts of the Appala- 

 chian system of mountains, especially in the section from Virginia 

 southward ; in the Archasan district of Missouri and Arkansas, and 

 in the vast region of highly metamorphic 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 val- 

 ley, and the rapid exhaustion of the soils of that district, will soon 

 give commercial importance to any sources of supply of phosphates 

 that may be found in any parts of the Cordilleras which are con- 

 venient 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 

 geological 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 saturation in sulphuric acid, but it is then mingled 

 with ammoniacal and other matter to increase its effect as a fertil- 

 izer. The result is, that although a ton of Carolina phosphate 

 now costs but six dollars, the average price of the manufactured 

 product to the consumer at the phosphate factories is about thirty 

 dollars 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 superphosphalizing on the phosphatic 

 matter is to make it more immediately absorbable by the plants. 

 If placed on the soil without any other preparation than grinding, 



1 Among the analyses recently made by the chemists of ahe Kentucky geological 

 survey is one which indicates the presence of phosphoric acid in considerable quanti- 

 ties in the limestones of coriiiferous age exposed at Stewart's mill, on Lulbegrud 

 Creek, in Clark County. This partial analysis, for which I am indebted to Mr. John 

 R. Proctor, the present director of the Kentucky survey, is as follows : viz., — 



Lime carbonale 21.3S0 



Magnesia 3.055 



Phosphoric acid 9-710 



Potash ' 830 



Soda 228 



Silicious nodules insoluble in acids 27.580 



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 essen- 

 tial 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 cosdy method of applying 

 phosphates has come about through the commercial history of arti- 

 ficial 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 ma- 

 terial than any other purchasable manures, and in ashort time they 

 established the type of commercial fertilizers. When the sources 

 of supply of these guanos became in part exhausted, artificial com- 

 pounds, 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 gave a quick 

 though temporary stimulus to the soil, enabling the farmer to ob- 

 tain the greater part of the return for his investment in the season 

 following the application of the high-priced manure. Very gener- 

 ally the fertilizer, guano or compounded material, was applied with 

 the seed or dibbled in the soil alongside the young plant ; so that 

 it would be immediately available in the first stages of its growth, 

 and, what is a more important consideration, that it might take 

 less of the substance to give the effect than if it were sown broad- 

 cast over the surface or mingled with the soil of the whole field. 



In this way a habit has been established in the art of using phos- 

 phates, as well as in the composition of the material, which, like 

 all commercial habits, is hard to overcome. The question to be 

 determined is as to the utility of phosphates with other modes of 

 treatment than those which are applied in the imitation guanos. 

 At present this treatment requires the commingling of the lime 

 phosphate with a number of costly substances. The manufacture 

 can only be advantageously carried on at points remote from the 

 districts where the materials are produced, and remote from the 

 fields where they are used, so that the costs of transportation are 

 great. The problems to be solved by the agricultural stations are 

 as follows : — 



(i) As to the effect, immediate as well as permanent, arising 

 from the application of ground phosphatic rock commingled with 

 other materials on soils used for the production of different crops. 



(2) As to the degree of comminution of the material which is 

 most advantageous. It seems possible that fine pulverizing may 

 take the place, in a measure, of superphosphatizing. 



(3) As to the effect of mingling the powdered rock with ordinary 

 barnyard manure, peat, and other similar substances. 



(4) As to the effect of lime phosphate used alone on soils con- 

 taining different mineral constituents ; as, for instance, those having 

 considerable proportions of lime carbonate, and those having but 

 little of that substance. 



(5) As to the proportion of the lime phosphate which it is neces- 

 sary to apply in order to produce different degrees of effect upon 

 the fertility of soils. 



It is desirable that these and other experiments should be tried 

 at a number of stations in different parts of the country, in order 

 that the needs of various crops may be considered, and the effect of 

 the fertilizers on different classes of soils ascertained. 



The effect of a small amount of lime phosphate on the fertility of 

 the soil is clearly great ; but, so far, we do not know with accuracy 

 the amount necessary to produce a given effect. The range in 

 phosphoric-acid contents in the soils of Kentucky, as determined 

 from many hundred analyses, varies from 0.540 to 0.061.^ In most 

 cases the fitness of the soil for grain-tillage is measurably propor- 

 tionate to the phosphatic contents. It seems almost certain, 

 though not yet demonstrated, that the greater part of the phos- 

 phatic matter in the soil is in the state known as insoluble and 

 that it only becomes in small part, year by year, soluble, or, in 

 other words, fitted for assimilation by plants. Whenever the soil 



ee report of Dr. Robert Peter i 

 , vol. V. 1878. 



I Reports of Geological Survey of Kentucky, 



