Original caption:  "Plate No. 9, TYPICAL SECTION SHOWING STATIONS AT INTERSECTION OF HIGH and LOW LEVEL SUBWAYS accompanying the report of Bion J. Arnold to the Local Transportation Committee of the City Council of the City of Chicago 1902.  Note that this subway plan was never built.
Bion J. Arnold <a rel="nofollow" class="external text" href="http://www.ieeeghn.org/wiki/index.php/Bion_J._Arnold">1861-1930</a>
Comments by Bion J. Arnold on Arthur S. Robinson, The Proposed "Inner Circle" System of Chicago Subway Terminals, <a rel="nofollow" class="external text" href="https://books.google.com/books?id=9mLOAAAAMAAJ&amp;pg=RA2-PA22">Journal of the Western Society of Engineers</a>, Vol. XI, No. 5 (Oct. 1906); page 622.