UP PLEMENTAL REPORT—HANGING ROCK DISTRICT. 887 
Shales or sandstones take the place of coal, and the steadiest seam is con- 
stantly undergoing changes of quality, from good to bad, or. to better, 
while the volume may expand and contract with rapid alternations. 
The elements that are generally counted available for identification in 
separate sections are sandstone ledges, beds of coal, and fire-clay, seams of 
ore and strata of limestone. 
The first named of these formations is the one that comes first into use. 
A sandstone twenty or thirty feet thick makes a conspicuous feature in 
every section. It can often be traced with the eye in unbroken outcrop 
for mile after mile. Though most commonly and confidently appealed 
to, a sand-rock needs to be used with great caution in establishing the 
identity of distinct sections. Ledges occupying different horizons fre- 
quently resemble each other so closely that the sharpest inspection can- 
not distinguish them. In mineral composition, indeed, there may be 
no difference whatever. Wherever the continuity of a sand-rock is lost, 
as in passing from one valley to another, it is an uncertain guide. 
Coal seams are universally recognized as having great powers of serv- 
ice in this way. Generally, more reliance is placed on them than on 
any other element, in constructing the section of any portion of the Coal 
Measures. Wherever there are marked peculiarities of a seam, as con- 
trasted with others with which it may be associated, in regard to quality as 
open-burning or caking, or in partings that are found persistent, or in less 
obvious points, as in the coler of the ash, theseamcan be trusted toa large 
extent, but it cannot be denied that the individuality required for identi- 
fication is often wanting, and in many fields, two contiguous seams may 
agree so closely in character, structure, and volume, as to make it impos. 
sible to determine them except by their stratigraphical relations. 
The same thing is true of beds of fire-clay. Occasionally a seam is 
so marked in quality or volume that it can be safely followed, but the 
same hill will often hold two or more seams that repeat each other in 
almost every particular. , | 
Seams of ore are often very well characterized, No onecan distinguish 
hand samples of the imestone ore of Lawrence county from specimens 
of the same seam in Perry and Hocking count es, where it is known as 
the Baird vein. Many other seams have locally such well marked pecul- 
iarities that wherever found they are confidently recognized. 
It is, however, to the last of the elements named above, that we owe 
most in this respect. The strata of limestone that are distributed 
through the Ohio Coal Measures, have long been recognized as, on the 
whole, the most available guides to a knowledge of the stratigraphical 
order of the several separate districts and of the field asa whole. Every 
geologist who has worked in this series has been obli.ed to recognize; 
