There's a correct name for the discolouration that a stone acquires when it's exposed to the elements, but it's a very fine line (as they say). Have a look at - http://www.themodernantiquarian.com/post/44542 - for instance, and imagine explaining that to a stoical archaeologist.
Not all stones that were once stood up have clearly defined 'socket holes' and packing wedges and that, of course, is one of the reasons they have fallen. For an example of this please look at - http://www.themodernantiquarian.com/post/43617 -.
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