Editing Amazon River (section)

=== The Lower Amazon ===
[[File:Manaus Encontro das aguas 10 2006 103 8x6.jpg|thumb|[[Meeting of Waters]]; the [[confluence]] of [[Rio Negro (Amazon)|Rio Negro]] (blue) and [[Solimões|Rio Solimões]] (sandy) near [[Manaus]], Brazil]]
[[File:Rio Solimoes and Rio Negro.JPG|thumb|Water samples of the [[Solimões]] (right) and [[Rio Negro (Amazon)|Rio Negro]] (left)]]

The Lower Amazon begins where the darkly colored waters of the Rio Negro meets the sandy-colored [[Solimões|Rio Solimões]] (the upper Amazon), and for over {{cvt|6|km|sp=us}} these waters [[Meeting of Waters|run side by side without mixing]]. At Óbidos, a bluff {{cvt|17|m|sp=us}} above the river is backed by low hills. The lower Amazon seems to have once been a [[bay|gulf]] of the Atlantic Ocean, the waters of which washed the cliffs near Óbidos.

Only about 10% of the Amazon's water enters downstream of Óbidos, very little of which is from the northern slope of the valley. The drainage area of the Amazon basin above Óbidos city is about {{cvt|5000000|km2|sp=us}}, and, below, only about {{cvt|1000000|km2|sp=us}} (around 20%), exclusive of the {{cvt|1400000|km2|sp=us}} of the Tocantins basin.{{sfn|Church|1911|p=789}} The [[Tocantins River]] enters the southern portion of the [[Amazon delta]].

In the lower reaches of the river, the north bank consists of a series of steep, table-topped hills extending for about {{cvt|240|km|sp=us}} from opposite the mouth of the Xingu as far as [[Monte Alegre, Pará|Monte Alegre]]. These hills are cut down to a kind of [[Terrace (agriculture)|terrace]] which lies between them and the river.{{sfn|Church|1911|p=788}}

On the south bank, above the Xingu, a line of low bluffs bordering the floodplain extends nearly to [[Santarém, Brazil|Santarém]] in a series of gentle curves before they bend to the southwest, and, abutting upon the lower Tapajós, merge into the bluffs which form the terrace margin of the Tapajós river valley.{{sfn|Church|1911|pp=788–89}}