The definition and identification of tills and tillites

The history and meaning of the terms till and tillite are discussed. The tilloid forming processes, such as rafting, glacial transport, cryo-tectonic transport, cryoturbation and ice solifluxion, tectonic transport, tectonic deformation, mass flow phenomena, turbulent fluid flow phenomena and selective weathering are examined. Criteria for the identification of tills and tillites are reassessed. Numerous large boulders which have penetrated and deformed a series of strata can be used alone for the determination of glaciation. Stratigraphic evidence alone may be extremely convincing but must be taken in conjunction with other evidence. The shape, size, surface and composition of clasts and the presence of striated pavements can be explained in several ways, but if present in sufficient quantity or of sufficient quality, may be used to justify or corroborate glaciation. Mudflows or turbidity currents may be indicative of processes other than glacial, but are likely to occur more frequently during glacial times.