I was referring to proof rock as possibly being Anglo Saxon.

On 6 Aug 2015 7:24 pm, Nancy Gish <[log in to unmask]> wrote:
"Stone" is Old English, but "touch" comes from old French and is first listed in the OED in the 14th and 15th centuries. So "touchstone" is Middle English but not Anglo-Saxon--an interesting compound of English and French after they merged.
Also, of course, a great comic figure in "As You Like It."
It seems to me so common as a way of testing or evaluating that it would not need a source.  Eliot was very familiar with Arnold, but the use would, I think, be common.