Martin (1992: 323-4):
In the following text for example, one activity follows another by law; in scientific discourse this relation is made explicit through conditional consequential relations (typically if/then).
[5:31] We saw that leaching was a very prominent process in all hot, wet, forest lands; in deserts because the rainfall is so low, it hardly occurs at all. Instead a reverse process may develop called calcification. Water may soak into the ground after rains and dissolve mineral salts in the usual way, but as the surface dries out, this water is drawn upwards like moisture rising through blotting paper. The salts then accumulate in the surface soil as this moisture evaporates; thus desert soils are often rich in mineral salts, particularly calcium, sodium and potassium. Provided the salts are not too concentrated (and their concentration is reduced under irrigation), they contain a plentiful supply of plant foods and can therefore be considered as fertile soils.
The logical structure of the activity sequence calcification outlined here is as follows:
i. If water soaks into the groundii. then it will dissolve mineral salts.iii. If it does, then if the surface dries outiv. then the water is drawn upwards.v. If it is, then if the water evaporatesvi. then salts accumulate in the surface soil.
 In the discourse semantics model, as these 'activity sequences' demonstrate, language (ideational semantics) is confused with context (field). These 'activity sequences' are ideational meanings, not the ideational dimension of culture. In SFL terms, the (second-order) field here is geography. The meanings of geography are semantics, or more precisely: a semantic domain. Halliday & Matthiessen (1999: 323):
… the semantic correlate of a contextual field is a domain. When we model the ideational semantics of a particular field, we create a domain model.
 No laws are presented in the geography text, and there is only one instance of a conditional relation.
 This is purported to be the 'logical structure' of the field of the first text. However, it is actually just another text that reconstrues the expansion relations of first text as exclusively enhancing: causal-conditional. The expansion relations could also have been reconstrued as, say, exclusively enhancing: temporal or as extending: addition.