They are two separate strands, but always worn together. Queen Mary (never one for understatement, I think) added a third.
The longer strand, Queen Caroline's, was put together from 5 or mor strands she owned, choosing the best pearls from each one. So even royalty couldn't end up with entirely even, matched pearls, as Caitlin says.
The close-up strand is definitely the pearls (from the royal collections website) and the wedding photo pretty definitely shows them, as Princess Elizabeth is known to have worn them. She also had seed pearls sewn on to her dress.
Queen Elizabeth is a great fan of pearls - even when she's not wearing the multi-million pound lot, she's almost always photographed wearing "lesser" pearl necklaces. "Lesser" only in the sense of a Royal jewellary box, though!
The Queen today, wearing pearls (so is the Duchess of Cornwall for that matter)
And just as she became Queen - she was in Kenya when her father died, 60 years ago this year:
And the day she took the Royal Oath, in February 1952:
Last month, touring King's Lynn in Norfolk:
And in December last year:
She keeps up an impressive pace - she's 86 years old this year, she's been Queen for 60 years, and married for going on 65 years. And she keeps up a lifestyle that would exhaust most people a third of her age.