24 BULLETIN 122, U. S. DEPARTMENT OF AGRICULTURE. 



(26) PENN SILT LOAM, SUBSOIL. 



No. 4 sand. — Minerals other than quartz, 14 per cent. Potash feld- 

 spars (orthoclase), 5 per cent. Muscovite, 7 per cent. Magnetite- 

 biotite, rutile inclosed in quartz, apatite inclosed in quartz, and albite- 

 oligoclase are also present. 



No. 5 sand. — Minerals other than quartz, 15 per cent. Potash 

 feldspars (orthoclase), 4 per cent. Muscovite, 6 per cent. Mag- 

 netite, biotite, tourmaline, oligoclase, zircon, epidote, hypersthene, 

 labradorite, and hornblende are also present. 



Silt. — Minerals other than quartz, 40 per cent. Potash feldspars 

 (orthoclase), 4 per cent. Muscovite, 15 per cent. Tourmaline, 

 biotite, epidote, hornblende, albite, and augite are also present. 



DISCUSSION OF THE MINERALOGICAL DATA. 



The general results of the mineralogical examinations support the 

 conclusions already given by McCaughey and Fry. 1 The soils of the 

 Limestone Valley and Upland province are unique in containing 

 quartz crystals with inclusions of calcite and iron oxide. In general 

 soils of the glaciated areas are higher in minerals other than quartz 

 than soils of the other areas. 



Apatite is reported in 11 out of the 26 samples. The average of the 

 phosphoric-acid content of the soils is 0.11 P 2 5 , whereas the average 

 of those in which apatite was not recognized is 0.15 per cent. This 

 indicates either that the phosphoric acid (P 2 5 ) of soils occurs in other 

 minerals either as a characteristic part or accidentally, or that a large 

 part of the apatite is in the clay group, and thus escapes detection. 



Types in which the titanium was larger or of about the same amount 

 in the surface as compared to the subsoil contained rutile or rutile 

 inclusions in quartz. The percentage of minerals other than quartz 

 is higher in the finer separates, and particularly is this true in soils 

 of the Piedmont Plateau province. The amount of minerals other 

 than quartz is greater in the subsoil than in the surface soil, for the 

 respective separates. 



Tourmaline is present in the particles coarser than clay in 18 sam- 

 ples. This mineral is particularly interesting for it carries boron as 

 an essential constituent. In some cases tourmaline occurs in rela- 

 tively large amounts, indicating the presence of boron in more than 

 mere traces. The micas, generally muscovite, occur in 24 samples. 

 Phlogopite, of which fluorine is an essential constituent, occurs in 

 soils Nos. 10, 11, and 12. Fluorine occurs in all micas in amounts 

 varying from traces to several per cent, and therefore we would 

 expect these soils to contain fluorine 



The amounts of potash feldspars and micas in various soils have been 

 determined by McCaughey and Fry, and is given in Tables III and IV. 



1 Bull. 91, Bureau of Soils, U. S. Dept. Agriculture (1913). 



