VALLEY OF THE AMAZONS. 
177 
vegetation of to-day, that I have no doubt, 
when examined by competent authority, they 
will be identified with living plants. The 
presence 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, con¬ 
taining 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 superincum¬ 
bent beds by a glazed crust of hard, compact 
sandstone, almost resembling a ferruginous 
quartzite. 
Upon this follow beds of sand and sand¬ 
stone, varying in the regularity of their strata, 
reddish in color, often highly ferruginous, and 
more or less nodulous or porous. They pre¬ 
sent frequent traces of cross-stratification, al¬ 
ternating with regularly stratified horizontal 
beds, with here and there an intervening layer 
of clay. It would seem as if the character of 
