My dictionary says "skitter" means "to dart or run quickly and lightly. But what does "skittering" mean when it's used to describe stones? For example:
"It's a teeth-clenching battle against lumps and bumps, shuddering, jarring ripping through arms, skittering stones and scary slopes."
I would guess that "skittering stones" were "small, dislodged stones bouncing down the slopes towards you".
But it may help if you supply more context. What kind of activity does this relate to, for instance?