Irish slip jigs and old time C tunes have no association, although I'm at the point in my musical development where I'm starting to have an interest in both tune types, which are sort of like "4th tier" or "4th rung" in their respective idioms. But once you get around to them they can be a lot of fun.
If you fall for Irish Traditional music you’re bound to come across slip jigs, hopefully sooner than later. Unlike the more common reels and hornpipes which are in 4/4 time, and jigs (and IMO slides) which are in 6/8 time, slip jigs are in 9/8 time – “pineapple, apricot, sausages; pineapple, apricot sausages”. To me slip jigs feel elusive and exotic…with an almost jazzy phrasing. The time signature can be challenging for the trad music blow-in with no classical music background to try and wrap his head around.
The first slip jigs you’re likely to encounter are The Butterfly, Foxhunter’s and Kid on the Mountain. However, at my local session they play at least three other lovely 9/8 tunes: Snowy Path, Boys of Ballisodare and Another Jig Will Do. I like all three of these slip jigs and they are some of the next tunes I’m going to be working on. Comb Your Hair and Curl It and A Fig For a Kiss are a couple other titles that come to mind.
Just as slip jigs aren’t the first Irish tunes you learn, old-time fiddle tunes in the key of C are only going to come up after you’ve worked through D, A and G. Some of the old-time jams I attend will occasionally spend some time in C, and there’s a lot beyond Billy in the Lowground, including Texas Gales, East Tennessee Blues, Spider Bit the Baby, Monkey in a Dogcart, Hell Broke Loose in Georgia, L and N Rag, High Yellow, Tennessee Mountain Fox Chase, and many more.