Marvellous reprint on Forgotten Futures of an article published in Harmsworths Magazine in 1899 by Somers L Summers, which imagines London partly sunk under the sea.
There are some simulated photographs of what it would look like. My favourite is the Palazzo degli Horse Guards
The story claims to have been inspired by a report in a Daily Paper that:
“Geologists say that the land upon which London is built has subsided 68 feet during the last 500 years. This doubtless is traceable to substratiform deposits, lunar attraction, or causes equally occult; but whatever it is, the figures 68 disarm suspicion. Assuming that the subsidence is still going on, one can imagine the metropolis some day sinking below Thames level and becoming a second Venice”. However, “the climax was certainly precipitated by the Governments action in allowing London to be undermined to such an extent when the new coal fields were discovered under the city in 1900.”
A curious early play of many of the issues that worry us now: Venice sinking due partly to the underground water taken out by the chemical inudstry; fears about flooding in London; etc. However this article is light-hearted and ends with the author waking up in the dentists chair after anaesthetic gas.