168 
PHYSICAL HISTORY OF THE 
heaval of the Andes took place, closing the 
western side of this strait, and thus transform¬ 
ing it into a gulf, open only toward the east. 
Little or nothing is known of the earlier strata 
ified deposits resting against the crystalline 
masses first uplifted in the Amazonian Val¬ 
ley. There is here no sequence, as in North 
America, of Azoic, Silurian, Devonian, and 
Carboniferous formations, shored up against 
each other by the gradual upheaval of the con¬ 
tinent, although unquestionably older palaeo¬ 
zoic and secondary beds underlie, here and 
there, the later formations. Indeed, Major 
Coutinlio has found palaeozoic deposits, with 
characteristic shells, in the valley of the Rio 
Tapajos, at the first cascade, and carboniferous 
deposits have been noticed along the Rio Gua- 
pore and the Rio Mamore. But the first chap¬ 
ter in the valley’s geological history about 
which we have connected and trustworthy 
data is that of the cretaceous period. It seems 
certain, that, at the close of the secondary 
age, the whole Amazonian basin became lined 
with a cretaceous deposit, the margins of which 
crop out at various localities on its borders. 
They have been observed along its southern 
