164 University Geological Survey of Kansas. 
cases, limestone is productive, more commonly perhaps in 
Oklahoma, near Bartlesville, than in Kansas; but these some- 
what unusual conditions should not be taken very seriously, 
as the total amount of oil and gas thus far obtained from shale 
and limestone aggregates but a small fraction of one per cent. 
of the total production. This is an important statement, not 
only from theoretical consideration but also from a practical 
one. Wells may be drilled here and there in many places, 
therefore, with a hope of finding oil or gas without being car- 
ried to so great a depth as would be necessary were the Chero- 
kee shales the only producers. Thus far in our development - 
no well west of Chautauqua county has been carried to so great 
a depth, and we are entirely ignorant regarding what the re- 
sults would be should such a well be drilled. In fact, we have 
no positive evidence that the Cherokee shales with their in- 
cluded sandstones exist as far west as Winfield, although the 
presumption is they do. 
The shale-beds in the Midcontinental field generally have a 
great lateral extent. Sand-beds, on the contrary, quite often 
have a limited lateral extent, or will be limited in one direc- 
tion more than in another. This is true to so great an extent 
that sandstone horizons are unreliable as stratigraphic in- 
dividuals for the purpose of general stratigraphic discussions. 
Therefore, in previous pages and in those to follow, it is con- 
sidered desirable to speak of productive sand-beds as being 
contained within certain shale-beds and the shale-beds alter- 
nating with limestone beds. The most extensive and continu- 
ous sandstone horizon in this part of Kansas is the Chautau- 
aqua sandstone, lying within the Lawrence shales. In places 
these sandstones are continuous for many miles, but by no 
means as extensively or regularly as the shale-beds including 
them. In northern Oklahoma other sandstones sometimes 
have a comparatively great continuity, such as the sandstone 
capping the hills west of Bartlesville and extending south- 
ward beyond Tulsa and northward throughout Chautauqua 
county, reaching east into portions of Montgomery county. 
The drill has revealed a similar set of conditions for under- 
ground sandstone. Here a sandstone occurs in comparative 
purity and satisfactory thickness, while a few miles away it 
may be entirely wanting. A careful study of surface condi- 
tions along the eastern outcropping of every shale-bed of con- 
siderable size in the entire field reveals the same conditions. 
