What’s Up With the Ending?

At the end of the novel, Crusoe returns to Europe, where he comes into a great deal of money from his sugar plantations. He then gets married, has children, and eventually revisits his island. The novel ends with this following note:

All these things, with some very surprising Incidents in some new Adventures of my own, for ten Years more, I may perhaps gave a father Account hereafter.

The last lines of the novel, then, are a promise of continuing adventures, and indeed, Defoe delivered just that when he wrote The Farther Adventures of Robinson Crusoe the very same year.