DM,
Looks like a stone that has been worked into square and is encrusted with some kind of wierd fungus. Lichens of some sort? The carvings may be intentional but, their meanings remain to be seen. What holds the carvings?
Squaring is natural. I am tempted to think the white, possibly caliched,but it may be lichened marks, are signs of something near but already gone, within to the right of the pic.
Just wondering..it could go either way if these are signs or natural.
That bottom one i know i have seen before but do not recall if it was natural or not..i call it a high heel...
I guess mainly it is sandstone mixed in with sedimentary debris rock.