2. The _thermoluminescence_ method. The chemical properties of certain minerals change when the minerals are heated to high temperatures. If they are heated again they will glow, and the amount of time they glow upon reheating depends on the amount of time that has elapsed since they were heated originally. As yet the rate has not been accurately calculated, nor is it yet understood what effect different kinds of soils and atmospheres may have on this rate. If the method is proven, it will be invaluable to archaeology since it will afford a way of dating pottery directly on an absolute time scale. 3. The _paleomagnetism_ method. When an object containing particles which can be magnetized is heated, the magnetic particles line up according to the earth’s magnetic field. When the object cools, the particles are trapped in this position. We know that the earth’s magnetic field is changeable, and that at different times it has been oriented in different directions. Work is now in progress to determine how the field has varied through time and how successfully one can date materials such as pottery or hearths which were exposed to high temperatures in the past by the difference between the present magnetic field and that trapped in the object. Museum of New Mexico Press Santa Fe 1965 _Illustrations by Mary Spencer and Phyllis Hughes_ Transcriber’s Notes —Silently corrected a few typos. —Retained publication information from the printed edition: this eBook is public-domain in the country of publication. —In the text versions only, text in italics is delimited by _underscores_.