Jim foley says, "The above book devotes less than 2 pages to this topic,
but there are surely many whole books about it."
He is absolutely right. However, the index fossils are widely used and, to
the best of my knowledge, not one book is written about them.
They seem to be used and no rules are given as to how to determine which
fossils are index fossils. Except if they appear to be short lived, then
they are.
If we do not take them seriously as "proof," then no harm done, but they
are crucial.
Russell T. Arndts