• 11.038 and slowly a part of the rock-wall gave way.

This sub-entry in OED can by hyphenated or not – in general use it can be used as a rock-face or as a wall build out of many individual rocks.  Where I live, that’s called a stone fence.

“rock, n.1.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/166697. Accessed 19 September 2017.