FOR many years it was the custom to regard the line of separation of the Palaeolithic and Neolithic periods as roughly corresponding to the geological division between the Pleistocene and Holocene; and even Mr. Peake's excellent historical summary (NATURE, Jan. 20, p. 104) does not make it clear why this position was ever abandoned. It is unsatisfactory, and a source of confusion, that the term Neolithic should be used in a broad sense by one generation, and in a very narrow one by the next—that in one case it covers several thousand years in many different lands, while in the other it varies enormously in length in different countries, and in England (where the term originated) it is whittled down to a few decades, with some risk of complete disappearance.