
The SciencesJuly 1, 1967
Pre-Columbian Ridged Fields
In four areas of tropical lowland in South America there are huge arrays of ancient earthworks. Many of them are ridges put up to farm land subject to seasonal flooding

Pre-Columbian Ridged Fields
In four areas of tropical lowland in South America there are huge arrays of ancient earthworks. Many of them are ridges put up to farm land subject to seasonal flooding

Natural Gas
In terms of energy the U. S. has more of this cheap, clean, convenient fuel than petroleum. A rapidly growing network of pipelines now bears it to almost all parts of the nation