How valueable is the book The Ancient World by David T Ansted?
The website http://used.addall.com is a useful rough guide to
the selling prices of used books, since it aggregates search
results from 20+ online booksellers, which include listings from
thousands of individual dealers.
As of 10/23/07, the print-on-demand reprint editions seem to be
going for $30-40 (US), and the original 19th century editions for
upwards of $500.
HOWEVER, keep in mind that the listings on Addall only take in
books that have *not* yet sold at the prices listed. If there are
only a few, freakishly high listings for a given title, it may be
that there is no demand for the title at that price.
ALSO, keep in mind that the price you'd get selling to a book
dealer will be less than the retail price that some collector might
be willing to pay.
A historian working on 19th century science would probably save
money by buying the reprint (being more interested in the text than
in the book as an object), so the market probably consists of
collectors only. If you're interested in turning the book into
ready cash, your best bet is probably to run an internet search for
"book dealers" + "rare" + "geology" (or "natural history") . . .
the result will give you some sense of who sells to collectors of
old geology books, and might be interested in making an offer.
Throwing it up on EBay *might* get you a serious bidder . . .
but the odds are against it in my experience.
(Professional Historian and Amateur Online Bookseller)