Halliday (2008: 158):
The complexity of spoken language is, as I put it, choreographic; it can build up quite elaborately structured clauses, and string these out in equally elaborate clause complexes, giving a commonsense picture of the world that is intricate but not dense: intricate in movement, like a dance, but not on the other hand very densely packed. It is rather explicit in showing the semantic relationships among its various components. By contrast, the complexity of written language could be described as crystalline: its clauses tend to be rather simple in structure, but they can be extremely dense, with the elements compressed into lengthy expansions of words, most typically nominal groups, and the semantic relations among the constituent elements very largely left implicit — for the informed reader to supply. I have referred to these two types of complexity as “grammatical intricacy” and “lexical density” respectively.