azhong wrote:: Would the semicolon “;” be better replaced with a comma “,” in contemporary English punctuation since it is separating subordinate clauses but not main clauses? Or is the semicolon still grammatical and preferred in order to keep the very long sentence clearer?
The semicolons are the best choice for keeping complex list items clear, especially since some of the items contain commas. The fact that the list items are subordinates doesn't have much bearing.
 The comma before “and” seems to be still grammatical but already habitually omitted now? Is the omission a historical evolution?
Usage isn't uniform in this case. It is true that the style guides I know wouldn't typically put a comma there (except to improve readability), but it's easy to find real-world examples to the contrary.
 I think the comma before a relative clause is no longer grammatical in contemporary English.
That isn't a relative clause; it's a subordinate clause expressing the result of the speaker's hypos. That said, that is a less common place to put a comma.
 What does which refer to here? It should be something plural according to its verb "were"? But how can breezes be in or out sight?
"Which" probably refers to the waves. However, you can sometimes talk about "seeing" wind in terms of its effects on the environment.
 "A few hours previous" seems ungrammatical now?
Not at all. For me, "previous" as an adverb sounds a little elevated.
N'hésite pas à corriger mes erreurs.