Appears that the date of manufacture would be somewhere between 1879-1926.
In case you haven't seen this yet, #7 and #14 mention Mill Hall, with some complicated history at the top of the list:
http://www.roseantiquetools.com/id1.html
From another source, SunGazette.com, "Mill Hall Part 1: Ax capital of world recalled", November 15, 2009, By David Kagan:
"...After Robert Mann settled in Mill Hall in 1848, he, along with Saul McCormick, who died in 1857, developed a single-bit ax factory that became the community's leading industry. Because of increased demand during the Civil War, the factory was enlarged. The business was destroyed by fire on Sept. 11, 1877, but R. Mann and Sons rebuilt by April 1878. In 1879, another building was added for the manufacture of double-bit axes."
"From a business that had started in 1849 producing just 20 axes per day, by 1892 single-bit axes were pouring out at a rate of up to 800 per day, with 75 workers at that "upper" factory. The "lower" factory building had 65 employees producing up to 400 double-bit axes a day.
Remaining in business until 1926, R. Mann and Sons eventually reached a peak annual production of 840,000 double-bit axes, becoming the world's largest supplier."
http://www.sungazette.com/page/content.detail/id/535344.html?nav=5014
The Bur Nor sounds like it belonged to the Burlington Northern Railroad.