Amazon.com description: Product Description: Salt is a resource that we often take for granted. Before refrigeration, people poured salt over meats to preserve them. Soldiers of the Roman Empire received their pay in salt. Even Christopher Columbus was on the hunt for salt when he landed in the New World. Salt is an essential element for life, too. Like water, our bodies need salt. The countries of North America have always had plentiful natural resources. But the exploitation of these resources comes at a cost, and in certain cases, some have wondered if that cost is too high. North American Natural Resources explores all facets of this vital aspect of our economy. Readers will investigate the natural history, human use, technology, environmental impact, and economic significance of the most significant resources on the continent. Each title in this series contains color photos, a full-page map, and back matter including: an index, further reading lists for books and internet resources, and a series glossary. Mason Crests editorial team has placed Key Icons to Look for throughout the books in this series in an effort to encourage library readers to build knowledge, gain awareness, explore possibilities and expand their viewpoints through our content rich non-fiction books. Key Icons are as follows: Words to Understand are shown at the front of each chapter with definitions. These words are then used in the prose throughout that chapter, and are emboldened, so that the reader is able to reference back to the definitions- building their vocabulary and enhancing their reading comprehension. Sidebars are highlighted graphics with content rich material within that allows readers to build knowledge and broaden their perspectives by weaving together additional information to provide realistic and holistic perspectives. Text Dependent Questions are placed at the