There is a type of book which operates both on an adult and a juvenile level. I am not thinking of books like Robinson Crusoe or Gulliver's Travels, which probe deeply into the human condition and to which the child may bring his own uncluttered and innocent responses, taking from the surface of the work an enjoyable fiction comprehensible within the limits of his own world. Nor do I have in mind those books (Alan Garner's The Owl Service may be one) which have been written with professional competence for a specific market, but which hold within them a range of interpretation that may seriously activate and perhaps even tax the critical and intellectual faculties of an intelligent adult. I am thinking of a third and rarer type of book, one which may well have been written in ignorance of the readership it will eventually find, and which...