THE NONMKTALLIC MINERALS, 241 



A "blue oehor," formocl by the (leconipositioii of tho Utica shjiles in 

 Lehioh County, Pennsylvania, has the foUowinj,^ composition: 



I<inition (water and carbon ) 9. 10 



Ciiuirtz 44. 50 



Combined silica 26. 25 



Alumina with traces of ferric oxide 17. 95 



Majinesia 94 



Alkalies, etc 1. 2() 



100.00 



A second variety, from 1^ miles northwest of Breinigsville, and 

 which was sold as a yellow ochre, yielded: 



Silica, 60.53; alimiina, 17.40; ferric oxide, 9.27; lime, 0.08; mag- 

 nesia, 1.92; water, 5.51; alkalies, 5.27. 



Origin and mode of occurrence. — These vary greatly. In some 

 cases deposits of this nature are formed by springs. Such result from 

 the leaching out from the rocks, by carbonated waters, of iron in the 

 protoxide condition and its subsequent deposition as a hydrated ses- 

 quioxide. In other cases they are residual products formed by the 

 removal by solution, of the lime carbonates of calcareous rocks, 

 leaving their insoluble residues — the clay and iron oxides — in the 

 form of a red, yellow, or brown ocherous clay. Again, they may 

 result from the decomposition (oxidation) of beds of pyrite (iron 

 disulphide) and from the decomposition of beds of hematite, and by 

 the disintegration and perhaps partial hydration of the more compact 

 forms of limonite. Still, again, they may result from the decomposi- 

 tion of schists and other rocks rich in iron-bearing silicate minerals. 

 The yellow ochers of the Little Catoctin Mountains, near Leesburg, 

 Virginia, are thus stated to be residual products from the decomposi- 

 tion of hydro-mica or damourite schists. 



A paint ore found near Lehigh Gap, Carbon County, Pennsylvania 

 (Specimens Nos. 01115, 63481, 03482, U.S. N.M.), though not properly 

 an ocher, may be described here for want of a better place. The 

 raw material is a didl shaly or slaty rock, of a dark gray color, sandy 

 texture, and quite hard, and if descriptions are correct is probably 

 an arenaceous siderite, or carbonate of iron. 



According to C. E, Hesse ^ the ""paint bed" is of unknown extent 

 except so far as indicated ])v outcrops along the southern border of 

 Carbon County, a])out 27 miles nortl^of Bethlehem, where it occurs in 

 a well-defined ridge of Oriskany sandstone. Along the outcrop the 

 beds are covered by a cap of clav" and by the decomposed portion of 

 the Marcellus slate. Beginning with this slate the measures occur in 

 the following descending order: 



a. Hydraulic cement (probably Upper Helderberg), very hard and 

 ■ compact. 



^Transactions of the American Institute of Mining Engineers, XIX, 1891, p. 321. 

 NAT MUS 99 16 



