By Alex Kirby BBC News Online environment correspondent

Day three of Alex Kirby's diary from the World Summit on Sustainable Development in Johannesburg.

This is the summit of superlatives.

It is, its organisers tell you, the biggest international gathering ever held, and I hope they're right.

It is all whites, and the only blacks are servants

South African commentator

I do not fancy elbowing my way through even more teeming masses than Johannesburg has produced.

To be fair, though, while the organisers were talking of 65,000 delegates and assorted hangers-on like me, one I met last night put the figure - after some research - at about half that.

'Most arcane' summit

But size is not everything.

I'm sure some highly suggestive Johannesburg advertiser has already announced as much - one imaginative builder's merchant's billboard near here offers for sale equipment to ensure "an erection that will withstand an enormous blow".

This is also probably the most arcane summit in the entire course of human history.

A disgruntled campaigner told us the part of the negotiations that had left him rocking on his heels: paragraph 19(e) of some document whose blushes we should spare, which he had found "probably the most unintelligible paragraph ever written by human beings".

Beat that.

The superlative that sticks in my mind, though, is the description of Sandton, the Johannesburg suburb where the summit is being held, as "the richest square mile in Africa".

Africa's a biggish place, but I don't doubt Sandton's claim.

A few years ago, when baleful apartheid still held South Africa in its coils, it used to be said that you'd see fewer black people in the centre of Johannesburg than in well-heeled Cheshire, in north-west England.

There are black South Africans aplenty in Sandton today, and black Africans from the length of the continent.

But most are delegates, police officers, or waiting at tables.

Summit of contrasts

A jaundiced commentator from South Africa's Free Market Foundation invoked the ghost of one of the architects of apartheid, Hendrik Verwoerd, a former white South African leader who was assassinated.

The summit organisers, he said, had "turned the place into a white group area with all signs of Africa removed. It is all whites, and the only blacks are servants."

There are, despite him, vestigial signs of unofficial black South Africans in Sandton.

There are the newspaper vendors, for instance. Some of them are young women, most with a child of two or three years in tow.

The mothers have to sell enough papers to pay their return fares from the townships and to cover the cost of buying the papers from the wholesaler before they can begin to think of making a few rands.

The children play all day in the fumes of the passing vehicles, only feet away - so long as their luck holds - from the hurtling traffic. This is a summit of contrasts, too.