34 AGRICULTURAL ANALYSIS 



The black phosphate also occurs in a bedded form and presents 

 several varieties. Among these may be mentioned oolitic phos- 

 phate, which has the appearance of a rusty, porous sandstone. 

 The general appearance of the ovules of which the mass is made 

 indicates that they were formed while lying free upon the sea 

 bottom. In the phosphatic limestone which at some points under- 

 lies the phosphate bed, the same ovules and rounded fossil casts 

 are seen scattered through the mass of calcite. Another variety 

 of this bedded stone is known as compact phosphate, resembling 

 a homogeneous, finely grained sandstone. The phosphatic grains 

 of this rock are so small that they are distinguished with diffi- 

 culty even with a magnifying glass. The composition of the rock, 

 however, is revealed in a thin section under the microscope, and 

 it is shown to be made up of small ovules and fossiled casts closely 

 packed together. The ovules are nearly all flattened and are ar- 

 ranged with their long axes parallel. 



Another variety is the conglomerate phosphate, which is closely 

 associated with the oolitic and compact varieties, often entirely 

 replacing them and consisting of beds of coarse sandstone or con- 

 glomerate containing various amounts of phosphate. These con- 

 glomerates are usually black or gray and the constituent grains 

 are embedded in a matrix of fine material. They vary in size 

 from extremely fine grains to coarse particles one-fourth of an 

 inch in diameter. They are partly phosphate ovules, similar to 

 those composing the oolitic rock, and partly quartz. The con- 

 glomerate also contains many weather worn pebbles which are an 

 inch or more in diameter and composed of hard, black phosphate 

 so fine grained and homogeneous as to resemble black flint. 



There is also another variety known as shaly phosphate, in 

 which the laminated structure is pronounced, the rock splitting 

 into extremely thin sheets. In other instances the layers are an 

 inch or several inches in thickness, having a black glazed surface 

 even more carbonaceous than the remainder of the rock. 



37. Occurrence of White Phosphates. The white phosphates ap- 

 parently present two types; namely, the breccia and the bedded 

 phosphate. Closer examination shows that the two varieties are 

 more nearly related than was at first supposed, and they are found 



