Looks like a classic early-century sort of flat cap, worn a lot by autoists and aviators back then. Like Lincoln Beechey....
https://upload.wikimedia.org/wikiped..._his_plane.jpg
Bought a nice one in Ireland a couple of years back...in fact, the men of the whole group I was with bought them. Got back to the US, and a friend told me that in Britain, these are known as "rat catcher" hats...as they're the type of headgear often worn by men of that class.
Edit: Found a site that advertises them as "
ratcatchers".
Ron "Squeek" Wanttaja