It's easy enough to measure. Take a good rod, patch it tightly with an oily patch, then run it through the bore a couple of times. When it's turning smoothly, run it to the end of the barrel and mark your rod with a marker. Start pulling the rod and when it's made one full turn, measure it. If it's 9", it's a 1:9. If it's 12", it's a 1:12.
As a7mmnut said, they were once 1:12, but the Marlin barrels are 1:9. I've got an Ilion barrel that's 1:9.