According to Wikipedia: 'Baum had decided to end the Oz series with The Emerald City of Oz in 1910, after six installments over the first decade of the twentieth century. The Sea Fairies was intended to be the first in a new series of fantasy novels, which Baum and Reilly & Britton continued the next year with Sky Island. Unfortunately for author and publisher, the two volumes of the new projected series did not meet with the same success as the Oz books previously had. The first edition of The