INTRODUCTION: Portland cement is one of Indiana's most valuable mineral products, third in value below coal and stone. In 1973, 2.5 million tons of portland cement valued at $47 million was produced in five plants spaced rather evenly from north to south across the state. The plants of Lone Star Industries, Inc., at Greencastle, of the Lehigh Portland Cement Co. at Mitchell, and of the Louisville Cement Co. at Speed and Logansport mine and process most of their own major raw materials. The Universal Atlas plant at Gary uses slag from nearby steel mills and limestone imported by lake freighter from Michigan. The history and growth of Indiana's cement industry dates back to about 1826 and is well documented in publications of the Indiana Geological Survey. Cox (1874) and Borden (1874) published early reports on the occurrence and properties of the natural cement rocks of south-central Indiana. Siebenthal (1901) compiled an excellent summary of the natural cement industry. Blatchley and Ashley (1901) published an informative account of the early use of marl in portland cement produced in northern Indiana. Many authors subsequently discussed the geology, technology, and statistics of the industry. The reader is referred to the following reports: Blatchley (1901), Mance (1917), Logan (1922), Patton (1951), McGregor (1958), and Rooney (1964 and 1966).