and has not yet been exhausted by hundreds of thousands of years
of weathering. It also has the advantage of being well mixed, for
generally it is the product of scrapings from many kinds of
rocks, each of which contributes its own particular excellence to
the general composition. Take Wisconsin as an example.* Most
parts of that State have been glaciated, but in the southwest
there lies what is known as the "driftless area" because it is
not covered with the "drift" or glacial debris which is thickly
strewn over the rest of the State. A comparison of otherwise
similar counties lying within and without the driftless area
shows an astonishing contrast. In 1910 the average value of all
the farm land in twenty counties covered with drift amounted to
$56.90 per acre. In six counties partly covered with drift and
partly driftless the value was $59.80 per acre, while in thirteen
counties in the driftless area it was only $33.30 per acre. In
spite of the fact that glaciation causes swamps and lakes, the
proportion of land cultivated in the glaciated areas is larger
than in the driftless. In the glaciated area 61 per cent of the
land is improved and in the driftless area only 43.5 per cent.
Moreover, even though the underlying rock and the original
topography be of the same kind in both cases, the average yield
of crops per acre is greater where the ice has done its work.
Where the country rock consists of limestone, which naturally
forms a rich soil, the difference in favor of the glaciated area
amounts to only 1 or 2 per cent. Where the country rock is sandy,
the soil is so much improved by a mixture of fertilizing
limestone or even of clay and other materials that the average
yield of crops per acre in the glaciated areas is a third larger
than in the driftless. Taking everything into consideration it
appears that the ancient glaciation of Wisconsin increases the