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This paper summarizes some of the information available covering the distribution of mineral aggregates. Because of the scope of the paper, it was considered necessary to compile a selected bibliography, which is included. The origin of aggregates is discussed on the basis of the method of occurrence, that is, glacial or water-deposited granular materials such as naturally occurring sands and gravels, and igneous, metamorphic, or sedimentary rock as regard solid-rock materials. Gravels and sands occur in glaciated regions in the form of kames, eskers, terraces, outwash plains, beaches, and moraines. The distribution of these materials, in turn, is confined largely to the northern tier of states—all of the North east, much of the Middle West, and the northern portions of the Great Plains as well as portions of the northern states of the Far West. In contrast, other forms of water-deposited materials are found extensively in the Atlantic and Gulf Coastal Plain, the Great Plains, the filled valleys of the West, and to a limited extent in the mountainous regions of both the eastern and western sections of the country. Bedrock materials, used for the production of mineral aggregates, occur in the West in the Columbia Plateau, the Colorado Plateau, and the mountainous regions; while in the East, outcrops of rock are widespread between the Coastal Plain in the east and south and the Great Plains to the west. Even in many sections of the glacial-covered region to the north, bedrock materials are quarried extensively, particularly where the glacial cover is thin. Igneous rocks, used for the production of mineral aggregates, are to be found in widely scattered sections of the country. Traprock, as well as other igneous material, is quarried extensively in the Connecticut Valley, in several sections of the Piedmont in the East, in the Columbia Plateau, and in certain sections of the Rocky Mountains in the West. Certain metamorphic rocks, such as quartzites, are found in South Dakota and Minnesota, and other desirable metamorphic materials are found in the Piedmont sections in the East and in many of the mountainous regions of the country. Limestone is the most important sedimentary rock used for aggregate production and occurs extensively throughout the “Ridge and Valley” region of the East, throughout the Middle West, Kentucky, Tennessee, the Ozark Plateau, and widely scattered areas in the Great Plains and some small areas of the Far West. Since blast-furnace slag is a by-product of the steel industry, its occurrence and distribution is mentioned only briefly. Likewise, lightweight aggregates— such as pumice, volcanic cinders, and vermiculite—are not discussed.
Woods, K. B.
Professor of Highway Engineering, and Associate Director, Purdue University, Lafayette, Ind.