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The band of limestone substratum that stretches across the Lehigh Valley is known as the Cement Belt, and by 1900 produced three-quarters of the nation's cement. These nine vertical kilns for the manufacture of Portland cement were built in 1893 by Coplay Cement, the company founded by the industry's pioneer, David O. Saylor. They operated for only a decade, closing in 1904 when rotary kiln technology made the vertical form obsolete. At that time the top thirty feet of the ninety-foot-high cylinders were removed, leaving them at the sixty-foot height they are today. The towering brick structures now stand in a public park, named for Saylor.