Searching for reference to Huxley quotation

I have been searching for some time and in vain for the origin of a quote from Huxley that I read years and years ago - I cannot recall where, or from which of his writings this phrase came - nor its precise wording, unfortunately! The line conveys that there are moments in the depth of human despair when one considers the works of even the greatest artists and masters in history and asks - "is this it?" Shakespeare is specifically cited as the final example, although I do not recall the other examples.

There comes a time when one looks at .........., at ........ at Shakespeare even and must ask - is this it?

I am aware that this is not a great deal to go on - I thought I would post this just in case anyone else has come across these disturbing lines in Huxleys writings and recalls their origin. I hope there is someone else out there who can inform me.