" This is the opening paragraph with the main world. It might mean that the action takes place in London and that this particular city is going to be described. Thus, if we add the main parts of the sentence it might sound as "the action takes place in London", "I"m going to speak about London" or something of a kind. However, the original sentence does not show in what tense the action is. The second sentence misses a predicate which might be "are", "have been", "were". The third sentence shows to be a noun phrase, because both "implacable" and "November" describes the noun "weather". On the whole the sentence describes the atmosphere of the story.
The first part of the forth sentence lacks both the subject and the predicate, so we could add "there is"/ "there was" in order to complete the sentence. However, "there" is only a formal subject since the actual subject is "much mud". The second part of the sentence is grammatically correct since there are both the subject "the waters" and the predicate "had retired". The remained part of the sentence could be modified as follows: As if it would not be wonderful to meet a Megalosaurus which was forty feet long or so and which was waddling like an elephantine lizard up Holborn Hill. Thus, we get a subjective sentence.
Four commas and a dash divide the fifth sentence into six parts. Here the main noun and a subject is "smoke", "lowering" serves as a predicate, "down" and "from" are the prepositions denoting direction. If we change every part of the sentence, we will get: Smoke was lowering down from chimney-pots; smoke was making a soft black drizzle; flakes of soot as big as full grown snowflakes were in the chimney-pots; snowflakes have gone into mourning for the death of the sun.
Every paragraph starts with the main words (nouns) indicating the focus of the paragraph. Sentences of the following paragraphs are formed mainly of noun phrases.
