TOPOGRAPHY AND GEOLOGY. 15 
shale interstratified with sandstone. A light sandy soil results from 
its disintegration. It serves as an excellent reservoir, for the wells 
that penetrate it usually find in it an abundance of good soft water. 
Fayetteville formation. — Next above the Batesville sandstone lies 
a formation consisting principally of black or dark-gray carbonaceous 
shale, at many places thinly laminated. Near its base there is gen- 
erally a thin bed of hard, dark gray or blue limestone, while its middle 
part commonly grades from a sandy shale to a true sandstone, and 
where the sandstone phase predominates this portion of the forma- 
tion is distinguished as the Wedington sandstone member. The 
shale is well developed in the valley of West Fork of White River 
near Fay etteviUe, from which it is named, and the Wedington sand- 
stone member is particularly prominent southwest of Fayetteville, 
in Wedington Mountain, where it attains a thickness of 150 feet — 
perhaps one-half the total thickness of the formation. The softness 
of the shale causes it to erode so easily that its outcrop is usually 
marked by a valley. Where exposed, the shale disintegrates readily 
and forms a black and fertile soil. The composition of the unweath- 
ered shale renders it suitable material for brick making. The shale 
beds are practically constant from the Oklahoma line to Sulphur 
Rock, east of Batesville. 
Pitkin limestone. — Above the Fayetteville shale or the Wedington 
sandstone in northern Arkansas there is nearly everywhere a thin, 
inconspicuous bed of limestone — the Pitkin — characterized by screw- 
like stems of the fossil bryozoan Archimedes. This formation is 
regarded as the highest in the Mississippian series. 
PENNSYLVANIA^ SERIES. 
Morrow formation. — Under the name Morrow formation are 
included several beds of limestone, sandstone, and shale which vary 
much in thickness, arrangement, and character, and are of but little 
topographic prominence. These beds lie just below the sandstone of 
the " Millstone grit" series of the Arkansas Survey, and, as a rule, 
form the middle part of the escarpment of the Boston Mountain 
range. South of Batesville, near Jamestown, these beds have a total 
thickness of about 200 feet, while in a section in the north face of the 
mountains, south of Fayetteville, they are about 400 feet thick. The 
soil derived from them is highly fertile, but the land, being for the 
most part very precipitous, is so badly located for agricultural pur- 
poses that it is not generally cultivated. It possesses, however, a 
fine timber growth and several available limestone beds. 
Winslow formation. — The Winslow formation lies upon the Morrow 
formation and makes the summit and southern slopes of the Boston 
Mountains, except in the deeper ravines where older rock- have been 
