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