156 
PHYSICAL HISTORY OF THE 
boulders, resting above the partially stratified 
metamorphic rock. Other excellent opportu¬ 
nities for observing this formation, also within 
easy reach from the city, are afforded along 
the whole line of the railroad of Dom Pedro 
Segundo, where the cuts expose admirable sec¬ 
tions, showing the red, unstratified, homoge¬ 
neous mass of sandy clay resting above the 
solid rock, and often divided from it by a thin 
bed of pebbles. There can be no doubt, in the 
mind of any one familiar with similar facts 
observed in other parts of the world, that this 
is one of the many forms of-drift connected 
with glacial action. I was, however, far from 
anticipating, when I first met it in the neigh¬ 
borhood of Bio, that I should afterwards find 
it spreading over the surface of the country, 
from north to south and from east to west, 
with a continuity which gives legible connec¬ 
tion to the whole geological history of the 
continent. 
It is true that the extensive decomposition 
of the underlying rock, penetrating sometimes 
to a considerable depth, makes it often difficult 
to distinguish between it and the drift; and 
the problem is made still more puzzling by the 
