The late Precambrian Vendian Glaciation may have been triggered by a worldwide fall of temperature following the locking up of carbon dioxide in Upper Riphean Dolomites. In this "anti-greenhouse" mechanism, the Vendian case appears to differ from Gondwana and Pleistocene events which are restricted to the poles and not worldwide in extent. In the Vendian, but not in the Gondwana or Pleistocene glaciations, thick dolomite deposits almost always precede the tillites. And dolomite stones in those tillites indicate even more extensive Upper Riphean dolomite sedimentation than outcrops preserved today. Immediately after the glaciation, dolomite sedimentation generally became less important than before. Attention is given to the geochemical problems relating to atmospheric carbon dioxide balance. The synchroneity of glaciations is discussed, with regard to their central importance in Precambrian stratigraphy. The need to consider glaciations individually and not generalize from one to the other is stressed.