latitude 66°, of great height, and crowned with gigantic bowlders.

Why did not the advancing ice-sheet drive these deposits southward
over the plains of the United States? Can we conceive of a force that
was powerful enough to grind up the solid rocks, and yet was not able
to remove its own _débris_?

But there is still another reason which ought to satisfy us, once for
all, that the drift-deposits were not due to the pressure of a great
continental ice-sheet. It is this:

If the presence of the Drift proves that the country in which it is
found was once covered with a body of ice thick and heavy enough by
its pressure and weight to grind up the surface-rocks into clay,
sand, gravel, and bowlders, then the tropical regions of the world
must have been covered with such a great ice-sheet, upon the very
equator; for Agassiz found in Brazil a vast sheet of "ferruginous
clay with pebbles," which covers the whole country, "a sheet of
drift," says Agassiz, "consisting of the same homogeneous,
unstratified paste, and containing loose materials of all sorts and
sizes," deep red in color, and distributed, as in the north, in
uneven hills, while sometimes it is reduced to a thin deposit. It is
recent in time, although overlying rocks ancient geologically.
Agassiz had no doubt whatever that it was of glacial origin.

Professor Hartt, who accompanied Professor Agassiz in his South
American travels, and published a valuable work called "The Geology
of Brazil," describes drift-deposits as covering the province of
Pará, Brazil, upon the equator itself. The whole valley of the Amazon
is covered with stratified and unstratified and unfossiliferous