accusative and ergative languages

[petegray]

Let me stress that this is a question, not a claim, since I have not the
slightest knowledge of any actual ergative languages.

On these topics:
(a) `John hit me and went away' &  `I hit John and went away'
(b) The distinction between passives and ergativity.

Consider a co-ordinate sentence with suppressed second subject:
(a) In an accusative language, or a language with a passive construction, it
appears as:
       A(agent)  verb(passive)  B(grammatical subject; logical object) and
verb
If the second verb is passive, this should mean that B suffers both actions
(and presumably A is the agent of both).   But if the second verb is active,
it means that B suffers the first action, then performs the second.  For
example, Latin:
    a Paula pulsatur Marcus et necatur (odd word order, but you get the point)
    by Paula is-beaten Marcus(subject) and is-being-killed.
and
   a Paula pulsatur Marcus et ridet
   by Paula is-beaten Marcus(subject) and he laughs.

(b) What happens in a truly ergative language?
       A(ergative)  verb(of action)  B(absolute)  and verb
Am I right in thinking that if the second verb can take an ergative subject,
A is the agent of both (and B is presumably the object);  whereas if the
verb cannot take an ergative subject (i.e. it is a description rather than
an action), then either B must be the subject (as Dixon claims for
Dyirbal?), or the sentence is meaningless or ungrammatical  (Is this the
case in Basque, Larry?)
    I guess that different ergative languages will interpret this in
different ways, but is there any mileage in pursuing co-ordinate sentences
in order to reveal a difference between passive languages and ergative
languages?

It seems to me that there are two differences:
(a) where A affects B for both verbs, the rules are different in passive and
ergative languages: in one the second verb must be passive, and in the other
it must be able to take an ergative subject.
(b) where A does not affect B for both verbs, we get totally different
meanings and structures.

Peter