Two distinct types of composite frost wedges occur in lake deposits of Taylor Valley. The oldest, characterized by an inverted pear shape is found only on lake (varve) and deltaic deposits antedating the building of the Ross terminal moraine. It is completely lacking on the Fryxell terraces without moraine cover deposits where the characterizing composite wedge has a specific rectangular form. Pre-Ross-terminal moraine varve and deltaic deposits were built up in a lake occupying the whole of Lower Taylor Valley. According to duration of evolution of the pear shaped wedges, this lake phase should have ended 4,000-5,000 years ago before Ross Sea 1 glacier advance. In between the lake and end morainic phases, erosional activity lowered the Fryxell lake area to at least its present depth and shaped the side gullies draining glacier melt-water. Fryxell terraces were built as deltaic formations during the successive stages of the dropping high water table of a new lake. Its present level must have been reched some 1,500-2,000 years ago, in the assumption that the lowest terrace level has developed in the same way as the higher ones.