intriguing drive system on this worn out 56 yr old still operating locomotive engine

Found on http://themanlyblog.tumblr.com/ via http://www.railpictures.net/viewphoto.php?id=475808&nseq=189

For a clearer photo of a restored Shay drive locomotive: http://justacarguy.blogspot.com/2014/07/the-shay-drive-design-of-gear-driven.html