UPPLEMENTAL 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 diflference 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 whichitmay be associated, inregardtoquality as 

 open-burning or caking, or in partings that are found persistent, or in less 

 obvious points, as in the color of the ash, the seam can be trusted to a 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, sfructure, 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 one can distinguish 

 hand samples of the limestone 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 

 wltole, the most available guides to a knowledge of the stratigraphical 

 order of the several separate districts and of the field as a whole. Every 

 geologist who has worked in this series has bgen obliged to recognize 



