THE LOWER COAL MEASURES. 133 
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By the use of the Roman numerals, as shown in the third column, 
numbers could be used, which in written form would be distinguished 
from the old series, but on the whole it is counted safe to adopt the 
Pennsylvania names, and they will accordingly be used in this report. 
An argument for their use can be found in the established rules of 
geological nomenclature. These names are first in the field. The name 
of a coal seam of great economic value ought to have as firm a tenure 
as the name of a sandstone ledge without economic value. If the name 
Mahoning sandstone is retained for a well-known stratum of sandrock, 
the name Freeport coal, for example, can scarcely be dropped from an 
equally well-known coal seam. Both are continuous by the same token, 
for the sandstone is the roof of the coal. 
But no system can be adopted that will enable us to dispense with 
synonyms. Fora long while to come, whoever writes on the coal seams 
of Ohio will be doomed to a wearisome repetition of synonyms, if he 
guards himself against being misunderstood. Many years must elapse 
before our geology can be freed from the confusion that has come into 
it through the premature application of numbers as the designations of 
coal seams. 
This system of notation proved acceptable to the people at large, 
as is attested by its rapid spread through all of our coal fields. Its 
scant list of numbers made it possible to apply them all in almost every 
district, so that the incongruities and contradictions of our geological 
literature are more than paralleled in jthe popular applications of the 
system. 
A system fof designating the coal seams {having been adopted, a 
brief and general description of the Ohio coal field will be given, and 
