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Underground Detroit: The Salt of the Earth

Jeffrey Syken

Since ancient times, salt has been key to human survival and commerce. The word “Salt,” itself, is derived from the Latin word “Sal,” from which the English word “Salary” comes (Roman soldiers received part of their pay in salt). The ancient Chinese used coins made of salt and in Medieval Europe, many Mediterranean people used cakes of salt as currency. Native Americans termed salt “White Magic,” following animal trails to “salt licks” during the hunt. Christ referred to his disciples as “The Salt of the Earth” and it’s still a Russian custom for newlyweds to fling salt into the corners of their new home to ensure health and happiness. Such is salt’s influence and importance to humankind. As the basis for all of the sodium compounds and most of the chlorine compounds, mineral salt has a myriad of direct and derivative uses, including food preservation, leather tanning, road de-icing, etc. and is invaluable to industry.

When the presence of a rock salt was discovered deep under the streets of Detroit in 1898, it began a decade-long struggle to create a shaft to gain access to the rich deposits. Time after time, the test well flooded and contractors abandoned the work, only to be taken up by new contractors. Finally, in September 1909, an engineer named Bradt, after many months studying the problem of stopping the sulphurous flow through the porous limestone, came up with the idea of injecting cement, under pressure, into the limestone. It worked, and the Detroit Rock Salt Company was in business. The success of the Detroit mine quickly caught the attention of a competitor, the International Salt Company, who purchased the mine and operated it until 1983. By 1914, 8K-tons of the 99% pure rock salt was being removed monthly.

About 400 million years ago, a vast expanse of salt deposits formed under much of what is today the State of Michigan, including the City of Detroit. Buried deep beneath sediments in the area known as the “Michigan Basin,” deposits formed horizontal salt beds, as ancient bodies of water receded and evaporated, rock and mineral deposits, liquid brines, petroleum, lime, clay, sandstone and coal were left behind. The basin was an arid area of Michigan’s Lower Peninsula, separated from the ocean by a natural bar of land. As the basin continued to sink lower into the earth, salt-laden ocean water repeatedly poured into the depression, where it gradually evaporated, forming miles of salt beds. Thus, during the early decades of the 20th century, Michigan led the nation in salt production and remains a leading producer of many natural salines, with the modern-day Detroit Salt Company an inheritor of that proud legacy.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

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