JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 128.235.251.160 on TueABSTRACT. In terms of frozen ground phenomena and their dependence on climatic parameters, Iceland occupies a very interesting position between the Eurasian and North American permafrost regions. In this paper two characteristic forms of frozen ground have been treated: large-scale polygonal ground and frost mounds of the palsa type. The investigation involves: 1) Interpretation of existing aerial photographs. 2) Experiments in recording polygonal patterns by airborne infrared line-scanning and special photographic techniques. 3) Field examination of selected localities. In Iceland, polygon formation of the frost-crack polygon type has occurred and is presently occurring without the presence of permafrost. The frost-crack process has increased during the last decade. The deposition of tephra and other eolian sediments and their sequence of layering offer excellent possibilities for analysing cryogenic disturbances of older soil surfaces and layers by studying vertical sections of Icelandic soils.Historical volcanic activity provides the special conditions necessary to date morphologic processes by tephrochronologic techniques; tephrochronology indicates that a period of polygon formation, more intense than the present, occurred in the 1600's and 1700's.In central Iceland, the present climate is adequate for the development of palsas. During the last 10 years the development of palsas has increased after a period of decreasing palsa formation between 1930 and 1950. CONTENTS