LIMES AND CEMENTS.


fact, the deposits, so far as known, lie on the southern edge of the
granitic area, along the margin of the glaciated area, mainly in
Wood county. As the proper utilization of these clays is dependent
upon a special knowledge of the precise character of each deposit,
general suggestions are of little value. Those interested are referred
directly to the local descriptions and analyses given in Vol. II,
pp. 468, 469, 471 and 476, and to the special paper of Prof. Irving
on the " Kaolin Clays of Wisconsin," published in the Transactions
of the Wisconsin Academy of Sciences, 1880.
While it is convenient and customary to speak of the crude ma-
terial of brick as clay, that which is really made use of is a mixture
of clay and sand, or, in the cream-colored brick, of aluminous clay,
calcareous clay or marl, and sand. This mixture is really a loam,
and but for the appropriation of that term as the designation of a
soil, it would doubtless be more generally applied to such mixtures.
Very many deposits present the right proportions of clay and sand,
either already mixed or in interstratified layers readily mixed in the
handling.
Pottery clays, suitable for pottery, common tile, etc., abound at
various localities, and some of the finer classes are apparently suited
for higher ceramic purposes.
III. LnES AND CEMENTS.
The several limestone series of Wisconsin furnish superabundant
material for the manufacture of quicklime, suitable for common
constructive purposes. The main practical question, therefore, that
claims attention here, relates to the selection of the best available
material, a matter too much neglected.
Chemical Composition. It was formerly supposed that pure car-
bonate of lime afforded the best material for the purpose, and that
the magnesian limestones were inferior; but extensive experience
seems to have satisfactorily demonstrated that the reverse is true.
At least, the great markets of this country are said to be now supplied
almost wholly by magnesian limes, to the exclusion of the simple
limes, even though the latter may be obtained nearer at hand. It
is possible that this may be in part due to greater freedom from
impurities, and to texture, but at any rate the former prejudice
against magnesia seems to have been ill-founded.
The presence of silica (sand) and alumina (clay) are objectionable,
not only as impurities, but because, by fusing with the lime, they
neutralize an equivalent portion of that, and are therefore more
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