In The Time Machine (1895), HG Wells imagined a future in which childlike aristocrats lolled in the sunlight while brutalised workers lurked below ground. In 2011, Paris has evolved its own milder version of the Wellsian "Eloi" (surface dwellers) and "Morlocks" (human moles).
On the elegant streets, and even in the Metro, the non-tourist population is largely white, middle-class and well-heeled. Go underground – below the Metro, below the sewers, below the catacombs, below the five-storey underground car parks – and you reach another world: a poorer world; a neglected world; a largely African and North African world.
The building of the Parisian regional underground railway system, or Réseau Express Régional (RER), started a half century ago this month. It now connects the suburbs, north, south, east and west, through 47 miles of deep tunnels beneath the capital, bringing suburban commuters into the heart of Paris and whisking travellers from suburb to suburb.
When I first lived in Paris in 1978, the RER, then three lines (now five), was a glittering show-piece. Because I live and work in the centre of the city, I have only occasionally used the RER since I came back to Paris 14 years ago.
The other day I had to help my sister-in-law deliver three schoolgirls to a mainline station in the southern suburbs of Paris. The girls were travelling from London to a scout camp in the French Alps and already dressed up very smartly in their French scout uniforms.
We travelled by the original RER lines, "A" and "B". I was astonished at how dilapidated the system has become: the platforms filthy; the walls crumbling; the carriages old and dirty. Built at pharaonic cost in the late 1960s and early 1970s, the central sections of the RER are now much dingier than the Metro, which was mostly built from the 1890s to the 1930s.
What was even more striking was the sociological and racial disparity between Paris at street level and this other Paris deep underground. The great majority of the passengers were of African or North African origin. Because the RER connects the multiracial "banlieues", it has become, outside rush-hours, a part of the banlieues, hidden 40m beneath the city.
That perhaps explains why, just like the banlieues, the RER has been neglected by successive governments of both left and right. There are grandiose plans under discussion to extend the system with a sixth, cross-Paris deep tunnel and a giant, outer-suburban circle line. New trains are to enter service on Line A this autumn. It would be nice if a small part of the billions promised for these schemes could be diverted to refurbishing, or at least cleaning, the heroically filthy RER interchanges at Châtelet, Gare du Nord, Auber and Etoile.
As so often, the presumed excellence of things French – in this case, public transport – is partly true and partly a myth. TGV services, 30 years old this year, are wonderful; the regional trains are poor. The Metro is mostly fine; the RER, run jointly by the French railways (SNCF) and the Paris Metro (RATP), is a disgrace.
When we reached Massy TGV in the Parisian far south, we strolled from the RER to a sparkling new mainline station. A young woman with long red hair, and a large, old-fashioned station master's hat perched precariously on her head, cheerfully shooed hundreds of scouts and other holidaymakers into a procession of powerful express trains. Then my sister-in-law and I strolled back to join the other Morlocks on the shabby RER.
A country where service has not been forgotten
On the other hand...a sense of public service persists on the French railways which you would be hard pressed to find on the privatised British network.
This weekend, I set out to reach my little house in Normandy by a combination of train and bus. But there was a problem. A tree had fallen on to the line between Paris and Caen, delaying all trains by an hour or more. I pointed out to the "côntroleur de bord" (guard) that I was going to miss the last bus and would be stranded in Caen.
The côntroleur was not a fat controller in a top hat but a thin, young controller with a rakish SNCF cap, which made him look like a professional golfer. He made a call on his mobile. When the train arrived in Caen, I was "pris en charge" (taken care of) by a young, cheerful blonde woman.
Like the young woman at Massy, she had an old-fashioned SNCF hat perched precariously on her head. Someone could write a monograph on SNCF hats.
The young woman bundled me into a cab and I was driven to my door, 30km away. The taxi journey must have cost the SNCF at least three times the value of my ticket from Paris.
A question of gender for the French First Baby
Carla Bruni-Sarkozy has given her first interview about her pregnancy to the newspaper Nice Matin. The baby – whose existence has still not been officially announced – was a "great surprise and a great happiness". She said she had also been surprised to learn in several French magazines that the baby, due in October, was a boy. Since neither she nor her husband knew its gender, this was a scoop indeed.
Ms Bruni-Sarkozy, ex-super model and already a mother of one, has been resting at the presidential holiday home at Fort Bregançon on the Mediterranean. She skipped the Monaco royal wedding. She skipped the Bastille Day celebrations in Paris. Even before her pregnancy, however, she was not the most active of Première Dames. She told Nice Matin she would be delighted if her husband was re-elected next May. Being the First Lady of France had turned out to be "much less tiring than modelling".