Origional caption:  "Fig. 38.  Panel Long-wall in Oklahoma."  Plan of a multi-panel advancing longwall mine, circa 1917, using a face conveyor and rail haulage.  The figure has been altered by moving the scale and legend.
C. M. Young
Percentage of Extraction on of Bituminous Coal with Special Reference to Illinois Conditions, <a rel="nofollow" class="external text" href="https://books.google.com/books?id=6wQTAAAAIAAJ&amp;pg=PA131">Engineering Experiment Station Bulletin No. 100</a>, University of Illinois, page 131.