PHYSICAL HISTORY OF THE AMAZONS. 413 
blue, and also black and white. It is from these beds that 
the Indians prepare their paints. These clay deposits as- 
sume occasionally a peculiar appearance, and one which 
might mislead the observer as to their true nature. When 
their surface has been long exposed to the action of the 
atmosphere and to the heat of the burning sun, they look 
so much like clay-slates of the oldest geological epochs that, 
at first sight, I took them for primary slates, my attention 
being attracted to them by a regular cleavage as distinct as 
that of the most ancient clay-slates. And yet at Tonantins, 
on the banks of the Solimoens, in a locality where their 
exposed surfaces had this primordial appearance, I found in 
these verv beds a considerable amount of well-preserved 
tt 
leaves, the character of which proves their recent origin. 
These leaves do not even indicate as ancient a period as the 
Tertiaries, but resemble so closely the vegetation of to-day 
that I have no doubt, when examined by competent author- 
' ity, they will be identified with living plants. The pres- 
ence of such an extensive clay formation, stretching over a 
surface of more than three thousand miles in length and 
about seven hundred in breadth, is not easily explained 
under any ordinary circumstances. The fact that it is so 
thoroughly laminated shows that, in the basin in which it 
was formed, the waters must have been unusually quiet, 
containing identical materials throughout, and that these 
materials must have been deposited over the whole bottom 
in the same way. It is usually separated from the superin- 
cumbent beds by a glazed crust of hard, compact sandstone, 
almost resembling a ferruginous quartzite. 
Upon this follow beds of sand and sandstone, varying in 
the regularity of their strata, reddish in color, often highly 
ferruginous, and more or less nodulous or porous. They 
