Record of Geology of Texas, 188 7 - 1896 . 
213 
Penrose, R. A. F., Jr. 
Jersey; Analysis of tephvoite from Mason county, Texas. [Relation of the 
oxides and silicates of manganese. iPloat ore. Commercial value of the 
ores — Analyses of manganese ores from Central Texas ; Analyses of manga- 
nese ores from the Spiller msine, Texas. Mode of Occurrence of the Man- 
ganese ores. iDescri'ption of Localities — The Spiller Mine; the Kothmann 
tract; Analysis of manganese ore from the Kothmann tract, Texas; Horse 
Alountain; Analysis of manganese ore from Horse Mountain, Texas. 
‘‘The manganese ores of Texas occur in the central part of the State, 
mostly in Mason, Llano, and San Saba counties. The different deposits 
are from forty to sixty -miles from railway transportation, and no ore has 
yet been shipped from any of them. Several places, however, have been 
prospected, especially the Spiller mine and the Kothmann tract in Mason 
county, and, to a lesser degree. Horse Mountain, in Llano county. 
“The ores are associated with quartzites and gneisses, tho-ugh micaceous 
and garnetiferous schists are frequently found in the neighborhood. The 
rocks are much disiturbed and dip at various angles, sometimes standing 
vertically. They are supposed to be of pa-e-Cambrian age. 
“The Paleozoic and Cretaceous rocks border this region on all sides, and 
areas of them frequently protrude far into, or cap hills of the crystalline 
rocks. 
“Mineralogical forms of the ores . — The manganese minerals of the Cen- 
tral Texas region occur in the forms of oxides and silicates. The latter, 
so far as yet determined, generally represent manganiferous varieties of 
garnet,' though the protoxide silicate of manganese known as tephroite has 
also been found. 
“The oxides of i}ianganese . — The oxides of manganese occur in either 
a massi\^ form or as a granular crystalline aggregate, the two being more 
or less intimately associated. The massive variety has a black color, a 
isjnooth coiichoidal fracture, and a hardness of 6 to 7. The orysballine 
variety is black, and often very soft, in which condition it represents pyro- 
lusite. The oxides aa-e generally associated with more or less silica, which 
sometimes amounts to from 15 to 25 per cent, and makes the true mineral- 
ogical nature of the ores doubtful. 'Dr. T. B. Comstock notes the existence 
of psilomelane, pyrolusite, and wad in the Central Texas region.” Pp. 
432-433. 
336. 
The Iron Deposits of Arkansas.^ 
Ann. Kept, ol the Geol. Snrv. of Arkansas for 1892, Vol. I. 
Little Rock, 1892. 
Texas, Analyses of Iron Ores, p. 15; Classification of Iron Oi'es in Ter- 
tiary Strata, p. 106; Greologic Relations of the Iron Ores in Tertiary 
Strata, pp. 105-106; Origin of Tertiary Ores, pp. 134-138. 
“The laminated ores are especially well developed in Cherokee county in 
Eastern Texas. They appear to have been derived largely from iron pyrites, 
assisted possibly in some cases by carbonate of iron, and glauconite. As 
talready stated, the ore directly overlies a large glauconite bed, and in this, 
and immediately above it, iron pyrites is of common occurrence. In some 
