[Ed Shacklee]

I wonder if one of my more erudite Spherian friends could help me out. I'm trying to figure out where these two lines from Frost come from --

on your isle that should be an isle
but isn't because it's an isthmus.

I think it was part of a small Christmas verse, perhaps written informally, which I stumbled across years and years ago, but I can't locate it anywhere.

Thanks either way,

Ed