Bowen Building, 62-74 E. Randolph.  W. W. Boyington, 1872.  (Photo Thomas Leslie)

Chicago came to be known as a city of steel, but well into the 1880s it remained a city of brick, which eliminated some of stone’s drawbacks but offered problems of its own. The clay soil that made foundations such a problem proved to be a generous provider of strong, fire-resistant building material for the city, and the first post-fire technical developments to influence the city’s tall construction involved brick and terra-cotta.

Taken from Chicago Skyscrapers, 1871-1934 (University of Illinois Press, June 2013).