Letter from Thomas Gold to Professor Harold C Urey, School of Science and Engineering, University of California, San Diego, PO Box 109, La Jolla, California, 92038 Discussing the clogging of powders in a vacuum in experiments at Oak Ridge and Cornell: 'the general conclusion that well outgassed powders would be very adhesive has been clear to us for several years now'. Notes his annoyance at Urey's colleague Kuiper 'using his limelight to discredit my views'. Sets out his position on the cratered surface of the Lunar Mares. The erosion process at work is that of surface transportation of dust and the final material 'is a crunchy one of some strength, but possibly not exceeding that of snow'. Refers to the startling nature of the Ranger photographs and how they bear out his interpretation of the Lunar surface. Terracing effects within the dust. 'For the fun of it I will actually make some models of this type of ground and send you photographs'. 14 September 1964