ABSTRACT
Guiana highlands. Thus an enormous lowland has been built up, most of it still less than fiv& hundred feet above sea-level. Although the lower Amazon flows through undulating country the upper basin is a smooth plain whose eastward slope is perceptible only in the sluggish movement of the rivers. Below the foothill country the plain is completely stoneless until the lower Amazon valley is reached, for the underlying rock is almost nowhere exposed and fine silt alone is carried by the slow-moving rivers.
