The thread below: "Muirfield: The Evolution" is an excellent study in golf course design, courtesy of Harry Colt.
I think the same can be said of Hugh Wilson's and William Flynn's alterations at Merion East subsequent to the construction of Wilson's original layout in 1912. There's a good map of the course, illustrating the changes to the original layout, on pages 104 and 105 in the book "Golf at Merion". Unfortunately, I'm unable to post it on this thread.
If anyone else can, feel free, for the benefit of all!
To start with, holes 10, 11, 12 all originally played across Ardmore Avenue. In 1922, the present 10th, 11th and 12th holes were created to eliminate crossing the road with golf shots. These changes -- particularly those to the 12th hole -- resulted in the creation of the present par 3 13th hole (in 1924), principally to shorten the walk from the new 12th green to the 13th tee.
The present 2nd green was also built in the early 1920s, lengthening the par 5 hole by 60 yards or so. (The left hand bunkers, just short of the green at Merion's 2nd hole were originally greenside.)
About the same time as the new 2nd green was built the par5 4th hole was also lengthened by some 50 yards at the tee end; and the eighth green was rebuilt also. Originally it sloped quite naturally, yet severely from front-to-back. Wilson originally placed a "sand trench" behind the green in order to catch balls (remnants of this "trench" can be seen today -- or at least when I was there a few years ago), but still the green was rebuilt with more of a back-to-front tilt.
It was also in the mid-1920s that Wilson started a completed revision of the course's bunkering, with the assistance of Flynn. Shortly thereafter Wilson died and, as we know, Flynn executed the revision of the bunkering.
The last major change to the original design was the rebuilding of the 1st hole, in 1929 -- changing it from a dogleg left to a dogleg right (it's present form).
Although ALL of the rest of Merion East's holes that remain true to Wilson's original 1912 schemes are intricate parts of the "puzzle", the aforementioned revisions have A LOT to do with the reverance we hold for the course today -- think about it: the 1st, 2nd, 10th, 11th, 12th, and 13th, holes!!!
Again, the changes to Merion East by Wilson and Flynn are an excellent study in golf course design... much like Colt's redesign work at Muirfield, and elsewhere.