Open-Air Laboratory.

America was a virtual scientific laboratory for Europeans. The astonishing and hitherto unsuspected presence of North and South America became the measure by which scientists tested ancient theories of the size and shape of the Earth, the extent of oceans, and the nature of the world's peoples. In 1590 the Spaniard Jose de Acosta speculated on the origins of the Native Americans in The Naturall and Morall Historie of the East and West Indies. The gigantic laboratory of America allowed extensive fieldwork in search of data about mountains, rivers, lakes, and bays. Explorers turned geographers and cartographers fanned out across the continent in a seemingly endless process of hypothesis and analysis.

Endless Mountains.

John Farrer's Mapp of Virginia in 1651 revealed that the exact nature of the North American continent was still largely unknown. His map showed the Pacific Ocean at...