$98 GEOLOGY OF OHIO. 
The Gore Limestone, which is found from thirty to forty feet above the 
Zoar, resembles the latter in some of its phases, and can easily be mis- 
taken for it. Like the latter, too, it is underlain with a coal seam and 
overlain with iron ore. As a limestone, it is chiefly found in Hocking 
and Vinton counties. It is often replaced by flint, though seldom by as 
heavy deposits as the Zoar horizon shows. Like that limestone, it is 
dark blue in color, but it is not as heavily charged with fossils as the 
Zoar. In Sections 25 and 26, Starr township, Hocking county, however, 
it yields very perfectly preserved fossil shells. It has been used to some 
extent as furnace flux, but it is inferior to most of the limestones of the 
district for this purpose. | 
This, then, is the geological frame-work of the district. The main 
elements, already named, are persistent, and cah readily be distinguished 
from each other. The accessory seams come in to facilitate the identifi- 
eation. A careful enough examination of these elements will, therefore, 
show the proper horizon of every portion of the field. 
The fact that the limestones already described are closely associated 
with seams of both coal and iron ore, has already been incidentally men- 
tioned. It is a point of so much importance that it deserves to be treated 
at more length. ; 
There are four elements of the Coal Measures that are the products of 
life, viz., scams of coal and ore, and beds of limestone and flint. The 
last two have been found to be interchangeable to a high degree in the 
review already made. There are, in fact, but two limestones of the main 
series that are not very frequently replaced by flint. Both limestone 
and flint show their organic origin unmistakeably, being often filled 
with remains of the marine life of the periods in which they were formed. 
It needs no argument to prove that coal is the product of ancient veg- 
etable growths. The microscope shows in coal the various tissues that 
belong to plants, and even enables us to estimate the relative proportions 
of these several tissues that make up a coal seam. 
A bed of iron ore is a less obvious sign of the former presence of veget- 
able matter than a coal seam, but it is net a less certain sign. Unlike 
coal, iron ore is not formed from the tissues themselves, but it is accumu- 
lated by means of such tissues. The iron that is diffused so generally 
through rock formations of all sorts, is rendered soluble by the presence 
and through the agency of organic matter, and by the same agency is 
gathered into seams of carbonate of iron. 
These three or four elements are intimately associated in all our Coal 
Measure rocks. This association recurs again and again in the series 
under consideration. Coal, limestone or flint, and ore, mark vital nodes 
in the series, these nodes being separated from each other by beds of 
