ABSTRACT
A greater extent of permafrost in the geologic past is known by inference from phenomena found to be associated with permafrost. Generally the permafrost thins abruptly to the north under the Arctic Ocean. It breaks into discontinuous and sporadic bodies as it gradually thins to the south. Sporadic bodies of permafrost may be relics below the active layer or may be forming in favorable situations in poorly drained finegrained materials on north-facing slopes. The mean annual air temperature required to produce permafrost undoubtedly varies many degrees because of local conditions. Surface features can be used with considerable degree of accuracy to predict permafrost conditions if origin of the surface forms are clearly understood. In areas of discontinuous permafrost, large annual ground-water supplies are more common either in perched zones on top of permafrost or in nonfrozen zones within or below the permafrost. Permafrost is commonly welcomed by the miners in lode mining, as it means dry working conditions.
