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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 Sat, ABSTRACT. Tafoni-like cavernous weathering forms have been encountered at 21 locations in Finland. Their size vary from caverns 1-6 m in diameter to pits a few centimetres deep and wide. The cavernous forms have been developed in a great variety of rocks: gneisses, granitoids, amphibolites and breccias. The weathering is physico-chemical. The weathering material usually contains some clay minerals, among which illite, kaolinite, vermiculite and mixed-layer clay minerals predominate. In a few places the formation of gypsum seems to cause salt weathering. The weathering processes in ceilings and walls are flaking and granular disintegration. They seem mostly to be caused by water freezing in micro-fractures combined with chemical weathering. The big tafoni are results of a two-step development. The original forms were weathering pockets in the basal parts of the preglacial weathering crust. The glacier dislodged blocks comprising weathering pockets and transported these erratics, which remained unbroken because the crust, filling the pockets, was frozen. After glaciation the pockets were emptied, and the weathering proceeded and alveolar weathering controlled by the ventilation in the tafoni. Small cavernous forms may evolve differently. Structural weaknesses of the rock, such as inclusions, breccia fragments, accumulation of easily weathered minerals and miarolitic cavities, might have developed small-scale tafoni-like forms during postglacial time, particularly in the coastal zone. The bottom deposits of some tafoni enclose microfossils. The interpretation of these deposits is complicated because of the exceptional sedimentation conditions and the possible mixing with older microfossils.

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