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Scheme environments

I haven't used scheme for a while, but I just read the Revised(3.5)
Report on the Algorithmic Language Scheme.  Some interesting things
have been added (or at least documented) since I last worked with
scheme in 1983.  But one function that appears to be missing from the
spec is (eval expression environment).  In particular, environments
are not explicitly discussed, though they are lurking in the
background of section 3.1.

I wanted to use environments to implement namespace hierarchies.  I
faintly remember that scheme used to support the notion of a
"package", but I could not find it in any of my old documentation.
Has this been removed?  Or have these things been left out of the spec
to allow different scheme implementations to define their own way of
dealing with these concepts?  MIT C-Scheme has an eval function that
takes the expected arguments, but I couldn't find any relevant
documentation beyond the revised report.

-Joshua Marantz
Viewlogic Systems, Inc.