Part I. Report of progress in 1869, by J. S. Newberry, chief geologist. Part II. Report of progress in the second district, by E. B. Andrews, assist. geologist. Part III. Report on geology of Montgomery County, by Edward Orton, assist. geologist.

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There is no doubt that these deposits will be regarded with increasing
interest as their advantages for architectural purposes come to be recognized.
The heaviest accumulation of this clay now known in Southern Ohio,
occurs near Springfield, Clarke county, and it has already been turned
to good account in the manufacture of " Milwaukee" brick.
3. FIRESTONE.
A stone that can endure the action of heat admits of many useful applications. Two of the bedded rocks of the county have considerable
local reputation as firestones, viz., the sandy limestones that make the
uppermost beds of the Blue Limestone series and the Clinton Group. This
latter rock certainly answers a tolerable purpose for chimney jambs and
kindred uses. It is not easy to see what there is in its composition that
enables it to resist unchanged the agency of fire, as the analyses appended
to the following section show it to be a true limestone of a good degree
of purity. Experience, however, abundantly demonstrates its value in
this regard. Chimney-jambs can be shown that have stood for 50 years
in service. Farmers are willing to transport it for miles to lay up the
arches of their sugar-camps. It must be added that the different beds
of the series have very different qualities in this respect, the middle and
lower layers furnishing the best firestone, and there is no doubt that the
-quality in its highest exhibition is local.
4. LIME.
As lime is the great cement employed alike in nature and by human
art, the sources of its supply are of more economical value to any community than are the supplies of building-stone and brick-clay even. All
the bedded rocks of the Miami Valley, and portions of the Drift as well,
furnish materials from which excellent lime can be made. It is needful,
however, to remark that the terms limestone and lime do not convey any
precise information as to the chemical composition of the substances to
which they are applied. Limestones always contain carbonate of lime,
it is true; but besides this, they generally contain various compounds
and various proportions of magnesia, alumina (clay), silica (sand) and
iron. The limestones of this region that can be burned into valuable
lime may be divided into two classes, according to their chemical composition.
The first group comprises those rocks that consist mainly of carbonate
-of lime, or that contain at least 85 per cent. of this substance.
The second group is made up of the dolomites or magnesian limestones,
which have at least 40 per cent. of carbonate of magnesia in their composition. Silica, alumina and iron are found in small and varying proportions in each division.