I worked on a print from this negative yesterday. I must have taken this in the very early 70's when the fountain was still very new. You can see in the image of the negative how it  had not been washed or properly fixed or something went wrong in the development.  Perhaps the film wasn't properly seperated on the reel and this little mass of unfixed silver particles had accumulated on the edges and were not properly treated by the fixer and left to develop over time to create a dense area on the edges.  This was only visible when light hit the negative at a right angle, but in the enlarger it created dense areas on the sides.  I also noticed how when I was taking the photograph my center weighted in camera light meter was reading for the vertical wall placing that at Zone V and that ended up over exposing the horizontal risers in the foreground that I tried to cut a mask to help burn in.  I've been reading Fred Pickers Zone VI workshop book from the early 70's on printing and may have just begun to grasp the meaning of  "The Zone System"when it comes to proper exposure.  It's embarassing to be practicing photography for so many years and then you run across the most basic concept, something you should have known right at the start and it comes across as a huge revelation that takes you back to square one.