What were actually the stump and the boulder in Narnia?

In "The Silver Chair" by C.S. Lewis, the stump and the boulder were enchanted creatures named Puddleglum the Marshwiggle and a stone giant respectively. They were friends of Eustace and Jill on their quest to rescue Prince Rilian. The stump and the boulder were important allies who helped the children along their journey in Narnia.