If I remember correctly that Horstmann backmark was used from 1893-1935. Your Great Seal button came out in 1901 but it wasn't until 1910 that a rim was added. From 1910-1917 the button was either gilt or black. Black only from 1917-1923 and gilt thereafter. I don't see any traces of a black finish on your button so I would say it dates from 1910-1917, 1923-1935.