his ongoing may be indefinitely continued. A notable and
picturesque instance of the march of a great dune may be had from the
case in which one of them overwhelmed in the last century the village
of Eccles in southeastern England. The advancing sand gradually crept
into the hamlet, and in the course of a decade dispossessed the people
by burying their houses. In time the summit of the church spire
disappeared from view, and for many years thereafter all trace of the
hamlet was lost. Of late years, however, the onward march of the sands
has disclosed the church spire, and in the course of another century
the place may be revealed on its original site, unchanged except that
the marching hill will be on its other side.

In the region about the head of the Bay of Biscay the quantity of
these marching sands is so great that at one time they jeopardized the
agriculture of a large district. The French Government has now
succeeded, by carefully planting the surface of the country with
grasses and other herbs which will grow in such places, in checking
the movement of the wind-blown materials. By so doing they have merely
hastened the process by which Nature arrests the march of dunes. As
these heaps creep away from the sea, they generally come into regions
where a greater variety of plants flourish; moreover, their sand
grains become decayed, so that they afford a better soil. Gradually
the mat of vegetation binds them down, and in time covers them over so
that only the expert eye can recognise their true nature. Only in
desert regions can the march of these heaps be maintained for great
distances.

Characteristic dunes occur from point to point all along the Atlantic
coast from the State of Maine to the northern coast of Florida. They
also occur along the coasts of our Great Lakes, being particularly
well developed at the southern end of Lake Michigan, where they form,
perhaps, the most notable accumulations within the limits of the
United States.

When blown sands invade a forest and the deposit is rapidly
accumulated, the trees are often buried in an undecayed condition. In
this state, with certain chemical reactions which may take place in
the mass, the woody matter is apt to become replaced by silex
dissolved from the sand, which penetrates the tissues of the plants.
In this way salicified forests are produced, such as are found in the
region of the Rocky Mountains, where the trunks of the trees, now very
hard stone,