GEOLOGY AND PALAONTOLOGY. 193 
‘with the table-lands of Guiana and Brazil;* that the subsequent 
upheaval of the Andes left estuary friths now marked by the three 
river systems ;f that the Andes did not reach their present alti- 
tude until after the deposition of the Amazon formation, though it 
was a slow movement in mass, for the beds are nowhere unequally 
tilted or dislocated ;+ that the archipelago on the north was for- 
merly united to the southern continent, and that it has since been 
an area of subsidence; § and that simultaneously with this subsi- 
dence was created the low watershed which now separates the 
Amazon and Caribbean waters. 
* Bates has shown that the geographical distribution of insects indicates that 
Guiana was formerly an island. 
+ The sediments from these straits near the ocean would have a purely marine 
character ; and Hartt observes that the clays and sandstones on the coast tie in 
with those of the Amazon. 
t This certainly follows, if the Pebas and Pichaua shells prove to be early ter- 
tiary. The clay beds ascend the eastern slope beyond the village of Napo, which 
stands 1,400 feet above Para, and in long. 77°. The red clay was not prominent 
on the Rio Napo till we reached long. 74°, and altitude of 550 feet, where there 
is a very high bank called Puca-urcu, or monte colorado, containing lignite, — una 
mina de carbon de piedra, says Villavicencio. This interstratified lignite is trace- 
able eastward as far as Tabatinga. Darwin says that the Pampean formation 
was accompanied by an elevatory movement. 
§ This is suggested by the South American aharastad of the West Indian 
mammals and mollusks. There are palzontological reasons for believing (Pro- 
ceedings of the Academy of Natural Science, Phila., 1868, p. 318) that the Carib- 
bean continent was not submerged before the close of the Post Pliocene. 
A.A. A.S. VOL. XIX. 25 
