The Whaleback sits within an abandoned coal strip mine.  The coal is gone, removed by mining, but the coal sat within folded layers of sedimentary rock.   The removal of the coal has exposed the surfaces of the folds.  The most prevalent layer is the carbon-rich shale of the Llewellyn Formation that was just below the coal.  The hump of the whaleback consists of this black shale which enables the folds to be seen in three dimensions.  There are also hematite nodules that can be found in the shale.