"Oh, this is nice," said Jill. "Just walking along like this. I wish there could be more of this sort of adventure. It's a pity there's always so much ahppening in Narnia."
But the Unicorn explained to her that she was quite mistaken. He said that the Sons and Daughters of Adam and Eve were brought out of their own strange world into Narnia only at times when Narnia was stirred and upset, but she musn't think it was always like that. In between their visits tehre were hundreds and thousands of years when peaceful King followed peaceful King till you could hardly remember their names or count their numbers, and there was hardly anything to put into the History Books.

---skip several paragraphs---

He talked of whole centures in which all Narnia was so happy that notable dances and feasts, or at most tournaments, were the only things that could be remembered, and every day and week had been better than the last. As as he went on, the picture of all those happy years, all the thousands of them, piled up in Jill's mid till it was rather like looking down from a high hill onto a rick, lovely plain full of woods and waters and cornfields, which spread away and away till it got thin and misty from distance.

From LB

I find it interesting that C.S. Lewis left some sizeable gaps in the history of Narnia, for example there is a big gap of time between Magician’s nephew and The Lion, The Witch, and The Wardrobe.

Between these two books, Prince Col becomes the first king of Archenland, outlaws from Archenland go south and start the kingdom of Calormen, Telmar is colonized by Calormenes, King Gale saves the Lone Islands from a dragon and becomes emporer of them, pirates from earth take over Telmar, and then the white witch returns to narnia in that order.

There is also a gap between Silver Chair and Last Battle.

A lot of outlaws are in the Lantern Waste, so towers are built to guard the area. Tirian's father Erlian was king sometime after that and was killed by a giant. Other than that I don't know what happens in between these two.

I think Lewis had so much time pass between some of the books to show what happens when new generations forget the miracles old generations experienced. In some of the situations, I think Lewis used the gaps as plot devices. For example, about two hundred years passes between SC and LB because no one who had lived to see the real Aslan would believe a donkey in a lion suit is Aslan.