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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times injured by the occurrence of crystals of iron pyrites, which weather
into brownish stains when exposed to the air, and disfigure the surface.
In addition to the kind of rock already named, there is in the county a
large supply of Niagara rock that falls short of the typical excellence in
hardness and color, but which still constitutes a very serviceable and
valuable deposit. These beds of inferior quality are sometimes the precise stratigraphical equivalents of the true Dayton stone; that is, they
immediately overlie the Clinton formation, but generally they occur at a
higher level in the series. The differences in color and hardness alluded
to seem connected with differences in chemical composition-the Dayton
stone being a nearly pure carbonate of lime, while the inferior grades
are composed of the carbonates of lime and magnesia. The color of
these last-named beds is not constant, various shades of drab and yellow
alternating with shades of blue, sometimes even in the same layer of
rock.
The boulders of the Drift are also available for building purposes.
They form, in some parts of the county, the main supply for foundations,
and when treated with skill give excellent results.
2. BRICK, DRAINING-TILE AND POTTERY CLAYS.
There is scarcely a section in the county, outside of the alluvial bottom
lands, that does not furnish, in its Drift beds, materials from which
bricks can be manufactured, but the yellow clays that cover the higher
table lands (the Niagara rocks) are decidedly to be preferred for this
purpose. In many instances the clay that is removed from a building
site can be converted into bricks of the best quality, with which the
walls of the dwelling can be constructed.
Beds of blue clay are also abundant, generally at lower levels of the
county, from which draining-tile and pottery can be made. For these
purposes the blue and yellow clays are generally mixed, the blue clay
imparting the necessary strength, and the yellow counteracting the tendency of the former to shrink and crack in the process of baking.
The importance of draining-tile in agriculture begins to be understood.
Hundreds of thousands of tiles are now manufactured annually, with a
steadily increasing demand.
A third variety of clay is found within the county, in quite limited
deposits compared with the preceding. It, also, is called blue clay,
but it differs-from the ordinary blue clay in containing no iron. It
is converted by burning into a cream-colored brick of the same gene
ral characters as the Milwaukee brick. It is generally very fine-grained,
and has been quite largely used as mineral paint. In composition, it
probably consists of little besides alumina, silica and lime.