24 GEOLOGY OF OHIO. 
These three limestones and the beds associated with them, as 
already described, constitute the most available guides to the order of 
the Lower Coal Measures. They all exist in normal development in 
Ohio, as has been already shown, and the only question as to their 
successful use turns on the possibility of identifying them with certainty 
in their varied and perhaps widely-separated exposures. Can any one 
of these limestones or any one set of the beds that have been grouped 
together, be clearly and positively distinguished from every other, or is 
there danger of confusing and confounding two or more distinct hori- 
zons? The answer to such questions is that the several elements and 
groups already named are so snarply distinguished and defined that no 
geologist who has at once an adequate knowledge of the coal measures 
in general, and of the particular district which he is examining, can be 
left in doubt as to any of these horizons wherever they are found in 
good development. | 
In the following diagram, Fig. VII, the usual relations of these 
several limestones to each other is indicated. The intervals given are 
those more commonly found in Northeastern Ohio, but it must be borne 
in mind that they expand rapidly towards the southeast. 
e 
The aim of the present chapter is to show a true order for the 
Lower Coal Measures of Ohio by the proper use of the leading and 
determinable elements to which attention has now been called, and by 
such other elements as shall be found adipted to the purpose. 
Beginning on the eastern border of the State we find in Mahoning 
county a geological section that is in all respects common to Ohio and 
Pennsylvania. The Mahoning river flows out of Ohio into Pennsyl- 
vania, opening a deep valley into which numerous tributaries descend 
from the high lands on either side, disclosing almost every foot of the 
strata that they cut in their numerous sections. 
The sections at and about Lowellville are clear and accessible, and 
they have been made to do geological service more than once. New- 
berry publishes a section from Lowellville as illustrative of the geology 
of the valley, in his report upon Mahoning county. (Geology of Ohio, 
vol. III, p. 804). White gives several sections from this vicinity in his 
report on Lawrence county and the Ohio line (Q 2, p. 219). 
