Lucy Fitch Perkins
The Cave Twins

One in a series of stories that introduce a period of history and a geographical location through the adventures of twins. Here, cave twins Firetop and Firefly take us to prehistoric days when man was a hunter and wore the skins of animals. One day they overhear their parents, Hawk-eye and Limberleg, planning to leave them in the cave with Grannie and go off on a trip of exploration. The twins follow them, and together they cross the river to unknown land. Hawk-eye fights off an attack of the monkey-like tree people, who don't know about spears like his, and the family reaches the sea. Out on a peninsula, they find themselves in an earthquake, and the next morning they discover that their peninsula has become an island, separated by a mile of sea from the mainland. They are trapped there. But it is a bounteous island, with no dangerous animals, and they find a good cave, learn to gather clams, and lead a fine life. Hawk-eye figures out how to make a canoe, and travels back to bring the others...