I used to spend my summers in the Adirondacks and would often catch snakes amongst other things. What I was told they were when I was younger was a black rat snake. However, that is a juvenile and I'm sure it's markings will change. It's been a long time and I'm not sure I remember the snakes I caught having the tannish markings on the rear of the head.
I think it is probably a redbelly but more pics would help, specifically showing the belly. Rebellies have a quite red belly; the worm snakes I've seen are more pinkish underneath. The slimness and smooth appearance suggest worm snake, and the half-dozen or so redbellies I've caught have been a varying tan to chocolate brown on the back (though they obviously come darker, see the pic Chris posted above), and they've generally been a bit thicker.