Studies on seasonal changes in the temperature gradient of the active layer of soil at Fort

structed mercury thermometers. Since then, numerous papers have been published on soil temperatures, with stress for the most part on soils of temperate climates and the economic aspects of the problem. As a result of the research, a number of factors, intrinsic and extrinsic, have been found to affect the change in soil temperature gradient throughout the year. Bouyoucos (1913, 1916) thoroughly and systematically reviewed the literature available at that time, Since then, Crawford (1952) has published a comprehensive review of the wealth of pertinent soil temperature research. In this review, he discusses the roles played by the effect of rainfall and melting snow, snow cover, surface cover, soil-moisture content, moisture migration, thermal conductivity and diffusivity, freezing temperature of soils, daily temperature variation, temperature inversion with depth, and frost penetration and retreat. Generally, his review indicates that foremost among the extrinsic factors affecting soil temperature is the source and amount of heat give