Sorry, it's cracked. Came on a 17" frame I bought to upsize my youngest daughter's bike. She started off with a 13", then I changed front triangle to 15" when she got bigger. Then again a 17" but used all the components from the 13" and 15" including the swing-arm since the 17" one was cracked. The frames all being Mount Visions meant all the parts of frame were compatible. The bikes have gone from 13" to 15" to 17" and all I changed each time was front triangle. Easy peasy.
The swing-arm, think it's 1999, on bike since the 13" is similar to to later 2000 swing-arm, the one I weighed, the difference is it has an additional vertical tube under v-brake mounts and the longer diagonal tube that is on later 2000 is shorter on the 1999.
Had intended getting it welded but not bothered as 1999 arm fits no problem. Might actually get it done as my oldest daughter and my wife have Marins. As do I. Me and daughter have 1998 Wolf Tracks, my wife a Wild Cat Trail. Would be an idea to have a spare.