Aimé Bonpland,
Personal Narrative of Travels to the Equinoctial Regions of America…
“ We find there a granitic sand, of a blackish-brown colour, which is covered in the forests with thick layers of rich earth, and on the banks of the river with clay almost impermeable to water. The soil of the Cassiquiare appears more fertile than that of the valley of the Rio Negro, where maize does not prosper. ”
