I cut down a foot-and-a-half-thick, fifty or sixty foot dead tree this morning ... with an axe. Specifically, the new Fiskars axe that perspicuity gave me. It took me maybe half an hour.
(Of course, it must be said that apparently no-one had told the tree how this was supposed to work. It dropped in the opposite direction to the one I'd planned, towards the back-cut instead of the undercut, and hung up in another tree for several hours before a gust of wind brought it down the rest of the way.)