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STATE GEOLOGIST. 95 
limestones may be found, at some point, almost all the distance between 
the Pittsburg and Meigs Creek coal. By far the largest and most rep- 
resentative veins, however, are those which lie close to the coals. 
All these horizons furnish local veins of sufficient thickness for 
economic quarrying or mining. But the usefulness of these deposits is 
undoubtedly much reduced by the fact that they do not appear to be well 
defined over large areas. In fact, within the limits of one section, it is not 
uncommon to find a stone cutting out and being replaced by shales, clays, 
or even sandstones, so that they may be regarded as lenses, or swamps, 
rather than persistent and well defined deposits, like the limestones of the 
lower measures. 
Nevertheless, these swamp deposits, while not uniform enough to 
make them valuable as stratigraphic guides, are in many places amply 
large to make them of possible economic value. In many places they 
cover a number of square miles, and thus offer all necessary opportunity 
for permanent industrial development. 
The analyses of samples taken from these veins are confined here to 
those which were found promising for this purpose. In many other 
points which were examined, the percentage of magnesia was found too 
high for cement work. The method of sampling employed was to cross 
section all the strata available for quarrying at the point sampled, so that 
the average composition of the entire mass might be known. This method 
has the merit of giving a broad view of the composition of the strata, but 
has the fault of oftentimes condemning the deposit, on account of the 
deleterious influence of some comparatively small stratum. Thus, it 
may very likely be found on further closer examination that the mag- 
nesia in many of the areas will be found concentrated in portions of the 
bed, and that a now unpromising vein may be made to yield a consider- 
able portion of stone of excellent quality. This list is therefore far from 
final as regarding the economic areas of stone of this district. The fact 
that such good results have been gotten in some places ‘should lead 
the cement prospector to look much more carefully into this territory 
in the future, and determine for each locality whether the magnesia 
contamination is local or general. A tabular statement of analyses of 
_these upper limestones is given in Table VI. 
MARL. 
The bulk of the supply of calcareous materials in the State is in the 
hard and geologically ancient form of limestone. But there is also to 
be considered the soft recent deposits known as marls. is 
These marl deposits occupy chiefly the beds of lakes or ponds. In 
most cases in Ohio, the lakes have been drained or dried up, so that the 
marl occupies a flat meadow, more or less covered over with soil and 
