PHYSICAL HISTORY OF THE AMAZONS. 409 
rivers of all these provinces must have been tributaries 
of the Amazons in its eastward course. The evidence for 
this conclusion is substantially derived from the identity 
of the deposits in the valleys belonging to these provinces 
with those of the valleys through which the actual tribu- 
taries of the Amazons flow ; as, for instance, the Tocantins, 
the Xingu, the Tapajos, the Madeira, etc. Besides the 
fossils above alluded to from the eastern borders of this 
ancient basin, I have had recently another evidence of its 
cretaceous character from its southern region. Mr. Wil- 
liam Chandless, on his return from a late journey on the 
Rio Purus, presented me with a series of fossil remains 
of the highest interest, and undoubtedly belonging to the 
cretaceous period. They were collected by himself on the 
Rio Aquiry, an affluent of the Rio Purus. Most of them 
were found in place between the tenth and eleventh de- 
grees of south latitude, and the sixty-seventh and sixty- 
ninth degrees of west longitude from Greenwich, in local- 
ities varying from four hundred and thirty to six hundred 
and fifty feet above the sea-level. There are among them 
remains of Mosasaurus, and of fishes closely allied to those 
already represented by Faujas in his description of Maes- 
tricht, and characteristic, as is well known to geological 
students, of the most recent cretaceous period. 
Thus in its main features the valley of the Amazons, 
like that of the Mississippi, is a cretaceous basin. This 
resemblance suggests a further comparison between the 
twin continents of North and South America. Not only 
is their general form the same, but their framework, as 
we may call it, that is, the lay of their great mountain- 
chains and of their table-lands, with the extensive inter- 
vening depressions, presents a striking similarity. Indeed, 
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