On these pages see Notebook M p.160. They seem to be following the agenda set out there for a ‘preliminary chapter’, and therefore to be later in time than the note there. The first dated note in M2 is 17th January at page 44. Notebook M p.161 is dated 31st January. The implication, and it is not implausible, is that Ruskin left blank these pages of M2, and used them later, perhaps after the beginning of February and towards the end of his time in Venice, to draw out conclusions about the nature and development of Gothic, and that this is a draft for a preliminary chapter on dentils, and on their relevance to the nature and development of Gothic.
Other suggested chapter topics / drafts are at Notebook M p.86 (Verities of Venice); Notebook M p.93 (94L) on Masonry; Notebook M p.117 on 5th Orders; Notebook M p.160 on Gothic Style; Notebook M2 p.19 (Torcello); Notebook M2 p.36 (Tracer); perhaps Notebook M2 p.37 (Ducal Palace); Notebook M2 p.53L (St Marks); Notebook M2 p.53 (Leaf Cornice).
[Version 0.05: May 2008]