KEL.l 
ARKANSAS. 
91 
DESCRIPTION OF THE IZAKD LIMESTONE. 
The Izard limestone is a smooth, fine-grained, compact, homogene- 
ous, nonfossiliferous, even bedded limestone, breaking with a con- 
choidal fracture. It is mostly of a dark-blue color, varying locally to 
buff, light and dark gray, and almost black. 
Partial analyses of Izard limestone. 
Insoluble in hydrochloric acid.. 
Carbonate of lime (CaC0 3 ) 
Carbonate of magnesia ( MgCO ;H ) 
Total 
From Polk 
Bayou. 
1.44 
97.97 
99.41 
Lithograph 
ic quarry, 
Lafferty 
Creek. 
0.34 
98.67 
2.14 
101. 15 
POLK BAYOU AND ST. CLAIR LIMESTONES. 
DISTRIBUTION. 
On the north side of White River these limestones outcrop over a 
somewhat irregular belt 80 miles or more in length and from 2 to 10 
miles in width, running across the central part of North Arkansas in 
a nearly east-west direction, and extending from Hickor}^ Valley in 
R. 5 W., to Mount Hersey in R. 19 W., with isolated outcrops as far 
west as Jasper, in R. 21 W. In Independence County, at the eastern 
end of the area, the outcrop is all on the north side of White River. 
It crosses White River at Penters Bluff, from which place it is found 
only on the south side of the river. Its northwestern boundary in the 
main is the fault near St. Joe. 
In the western part of its area the bed is comparatively thin, its 
maximum thickness being exposed at Penters Bluff. The western and 
lorthwestern limits of the bed are fairly well defined. On the south 
t dips beneath the overlying Mississippian beds of the Boston 
Mountains. 
On the south side of White River, as on the north side, the marble 
utcrops along the narrow, winding watercourses. On both sides of 
the river the rocks have a gentle south dip, so that as the northern 
imit of the bed is approached the limestone bed occurs higher and 
igher up the hillsides until it is finally displaced by the underlying 
Ordovician rocks. On the south side of the river the limestone grad- 
ually descends to the beds of the streams, where it dips away gently 
toward the south, disappearing beneath the overlying Mississippian 
■rocks. Except where concealed by the chert debris, the limestone 
outcrop on the south side of the river is continuous as far west at least 
as R. 12. 
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