the Rio drift, is seen resting between it
and the underlying sandstone. In some places this bed of pebbles even
intersects the mass of the clay, giving it in such instances an
unquestionably stratified character. There can be no question that this
more recent formation rests unconformably upon the sandstone beds
beneath it; for it fills all the inequalities of their denudated
surfaces, whether they be more or less limited furrows, or wide,
undulating depressions. It may be seen everywhere along the banks of the
river, above the stratified sandstone, sometimes with the river mud
accumulated against it; at the season of the _enchente_, or high water,
it is the only formation left exposed above the water level. Its
thickness is not great; it varies from twenty or thirty to fifty feet,
and may occasionally rise nearly to a hundred feet in height, though
this is rarely the case. It is evident that this formation also was once
continuous, stretching over the whole basin at one level. Though it is
now worn down in many places, and has wholly disappeared in others, its
connection may be readily traced; since it is everywhere visible, not
only on opposite banks of the Amazons, but also on those of all its
tributaries, as far as their shores have been examined. I have said that
it rests always above the sandstone beds. This is true, with one
exception. Wherever the sandstone deposits retain their original
thickness, as in the hills of Monte Alegre and Almeyrim, the red clay is
not found on their summits, but occurs only in their ravines and
hollows, or resting against their sides. This shows that it is not only
posterior to the sandstone, but was accumulated in a shallower basin,
and consequently never reached so high a level. The boulders of Errere
do not rest on the stratified sandstone of the Serra, but are sunk in
the unstratified mass of the clay. This should be remembered, as it will
presently be seen that their position associates them with a later
period than that of the mountain itself. The unconformability of the
ochraceous clay and the underlying sandstones might lead to the idea
that the two formations belong to distinct geological periods, and are
not due to the same agency, acting at successive times. One feature,
however, shows their close connection. The ochraceous clay exhibits a
remarkable identity of configuration with the underlying sandstones. An
extensive survey of the two, in their mutual relations, shows cl