Ge/ies(s of Irnii-(/r' s. — KiiuhuJI. 351> 
also sometimt's otherwi.se identified. Aocordiiiii to ()rt(jn. tliis is 
the (h'a}' limestone of Xew])errv. the Pntnam Jlill limestone of 
Andrews, the Ferriferous limestone of the same author, and the 
(Jrayand Ilanging-Rock limestone of Orton. The iron-ore, with 
which parts of this limestone are replaced, both in the form of 
siderite and of its altered product, is identified with the (Marion 
ore and liuhrstone ore of western Penns\'lvania, the IJaird ore of 
the Hocking Valley, the Limestone-ore of southern Ohio and the 
Tapper limestone-ore of north-eastern Kentucky. Over 2U(> 
blast-furnaces in these regions have drawn a supply of iron-ores 
from this particular horizon.* The average thickness of the re- 
placements in southern Ohio is, according to Orton, about lU 
inches, and further to the north aliout S inches, tiiough said l)v 
Hunt to l)e often tw(j oi- three times these averages, as in A'intou 
County, t 
Superior portions of the T'})per and Lower Freeport lime- 
stones of the Lower Cotd Measures are likewise commonly re- 
placed with siderite. This passes l)y alteration into limonite. 
sometimes in the form of concretionary Idocks or nodules from 
exfoliation or weathering of prismatic blocks, separated by con- 
traction due to chemical transformation. Several horizons of 
sideritic limestone are identified in the same series in Pt'unsyl- 
vania. West Virginia and Maryland, more or less distinctly 
graduating into non-feiTiferous limi'stone. Among similar occur- 
rences in the Lower Barren measures is the Johnstown siderite 
or ferro-calcite, identified with the Mahoning .sandstone groui». 
!Mr. Bayard T. Putnam, referring generally to the limonites of 
the Coal Pleasures of Pennsylvania, remarks that they occur 
ah>ng the outcrops of limestone-beds, and are in general sini[)lv 
the weathered outcrops of .seams of carl)onate-ore.l 
AV)ove the horizon of the Sub-carlu>iiiferous limestone in Ohio. 
which has been shown to be replaced in part with siderite or its 
drivatives, that is, between this hoiizon and that i)f the Ferri- 
ferous limestone, several limestones of the Congjonu'rate series 
are likewise apt to be repla«'e(l with siderite in a more oi' less. 
altered state. Such occurrences are notablv the Zoar or Blue 
*()rton, liev. of Stratigraphical Geol. of eastern Ohio, Columbus, 
1880, 29. 
tMin. Res. of the Hocking Valley, Boston, 1881, 44. 
XV. S. Census, 188G, xv. 202. 
