Martin & Rose (2007: 110):
In general the drift in meaning, by means of grammatical metaphor, has been from reality as processes involving people and concrete things, to reality as relations between abstract things, as with the transference from marrying as process to marriage as thing. …
There is a set of regular principles for creating ideational metaphors — for reconstruing one kind of element as another. The most common include:
(1) a process or quality can be reconstrued as if it was a thing
(2) a process, or a quality of a process, can be reconstrued as a quality of a thing
These are ideational metaphors of the experiential type, i.e. they are concerned with elements of figures. Ideational metaphors of the logical type are concerned with reconstruing a conjunction between figures as if it were a process or thing.
 To be clear, here Martin & Rose confuse the metaphorical realisation of a figure ("processes involving people and concrete things") as a group or word (marriage) with the elemental metaphor of a Process realised as Thing (marriage).
 To be clear, the actual range of elemental metaphor is set out in Halliday & Matthiessen (1999: 245):
 To be clear, the authors' differentiation of ideational metaphor as either experiential or logical is invalidated by the inclusion of experiential categories (Process or Thing) in what they regard as logical metaphor.