An Obscure Wolfe Quotation

Somewhere in one of his books of essays and shorter tales, he discusses some time travel motifs. He mentions the problem of someone time traveling from one ancient time period to another. Like going from Shang Ching to the age of Ming China. (Not his example, but mine) Can anyone remember what essay and in what book? I'd like to track down that idea. Thanks a lot Lupine pack Pippen