There was also an early (pre-Civil War) cluster of 5'6" broad gauge lines in Maine. These included the Penobscot & Kennebec RR (1845) and the Androscoggin & Kennebec RR (1847), which merged to form the Maine Central RR in 1862. Broad gauge was so dominant in Maine that it was apparently common in that era to refer to SG railroads as "narrow gauge". This is ironic because the last of the Maine Central broad gauge wasn't converted to SG until 1871, just a few years before the construction of the first of the Maine Two-Footers, the Sandy River RR, in 1879.
-Philip Marshall