In the postscript to his paper on the Post-Pliocene Formation of the Isle of Man, Mr. J. A. Birds takes exception to my classification of the Manx drifts. He states that, “ a priori, is it not against Mr. Horne's view of his Lower Boulder-clay being really such that there should be intermediate formations of sand and gravel when the cold was at its extreme, and the ice, according to his showing, from 2000 to 3000 feet thick?” To those who are well acquainted with the appearances presented by interglacial deposits, this objection cannot have any weight.