[DicIfTEx]

I believe your modernisation attempt misinterprets the dino reference and its connection to the the previous clause about the floods; should it not rather be something like Mud overflowed the streets, as though the waters had only just retired from the face of the earth and it would not be shocking to meet a dinosaur etc. etc.

Although, as the comments on the original post discuss, this does rely on background knowledge that when Dickens was writing, there were popular theories associating dinosaurs with the Biblical flood.

For my part, I confused 'Megalosaurus' with 'Megalodon' and pictured a large shark stranded writhing on Holborn Hill by the sudden loss of its waters; an error which, paradoxically, helped me get closer to the intended meaning (which was, we know now, itself incorrect).