Edgar Allan Poe's 1849 short story. There's not much in the way of ruins in the tale but there are many humourous instances of someone from the future misunderstanding things considered common knowledge in contemporary society (i.e. the nineteenth century USA).

Here's link to Mellonta Tauta in Google Books. What follows is the account and interpretation of an inscription from Manhattan Island (New York).

Well, these few details are nearly all that have descended to us respecting the ancient Knickerbockers. It seems, however, that while digging in the centre of the emperor's garden, (which, you know, covers the whole island,) some of the workmen unearthed a cubical and evidently chisseled block of granite, weighing several hundred pounds. It was in good preservation, having received, apparently, little injury from the convulsion which entombed it. On one of its surfaces was a marble slab with (only think of it!) an inscription—a legible inscription. Pundit is in ecstasies. Upon detaching the slab, a cavity appeared, containing a leaden box filled with various coins, a long scrool of names, several documents which appear to resemble newspapers, with other matters of intense interest to the antiquarian ! There can be no doubt that all these are genuine Amric- can relics belonging to the tribe called Knickerbocker. The papers thrown on board our balloon are filled with fac-similes of the coins, MSS., typography, &c. &c. I copy for your amusement the Knickerbocker inscription on the marble slab :—

This Corner Stone of a Monument to the
Memory of
GEORGE WASHINGTON,
was laid with appropriate ceremonies on the
19ra Day Of October, 1847,
the anniversary of the surrender of
Lord Cornwallis
to General Washington at Yorktown,
A. D. 1781,
under the auspices of the Washington Monument Association
of the city of New York.

This, as I give it, is a verbatim translation done by Pundit himself, so there can be no mistake about it. From the few words thus preserved, we glean several important items of knowledge, not the least interesting of which is the fact that a thousand years ago actual monuments had fallen into disuse—as was all very proper—the people contenting themselves, as we do now, with a mere indication of the design to erect a monument at some future time ; a corner-stone being cautiously laid by itself " solitary and alone" (excuse me for quoting the great Amriccan poet Benton!) as a guarantee of the magnanimous intention. We ascertain, too, very distinctly, from this admirable inscription, the how, as well as the where and the what, of the great surrender in question. As to the where, it was Yorktown (wherever that was, and as to the what, it was General Cornwallis (no doubt some wealthy dealer in corn). He was surrendered. The inscription commemorates the surrender of—what ?—why, " of Lord Cornwallis." The only question is what could the savages wish him surrendered for. But. when we remember that these savages were undoubtedly cannibals, we are led to the conclusion that they intended him for sausage. As to the how of the surrender, no language can be more explicit. Lord Cornwallis was surrendered (for sausage) " under the auspices of the Washington Monument Association"—no doubt a charitable institution for the depositing of corner-stones. But, Heaven bless me ! what is the matter ? Ah, I see—the balloon has collapsed, and we shall have a tumble into the sea. I have, therefore, only time enough to add that, from a hasty inspection of the fac-similes of newspapers, &c. &c., I find that the great men in those days among the Amriccans, were one John, a smith, and one Zacchary, a tailor.

Once again, thanks to Ray Girvan for putting me onto this. (See Humour and the Elusiveness of the Past.)