drift

drift deposit of mixed clay, gravel, sand, and boulders transported and laid down by glaciers. Stratified, or glaciofluvial, drift is carried by waters flowing from the melting ice of a glacier. The flowing water sorts the particles, generally depositing layers of coarser particles nearer the point of origin. Till, or boulder clay, which makes up the greater part of the drift, is unstratified, consisting of disorganized heaps of rocks that range widely in size. Till is deposited directly by the glacier itself without water transport. The drift may take the form of a drumlin , a kame , an esker , a moraine , or an outwash plain; its thickness varies noticeably from place to place and is not dependent upon topographical factors. Presence of drift proved useful in establishing the existence of time periods when large parts of the surface of continents were covered with glaciers (see glacial periods ). Large sections of continental Europe and North America are covered by drift.

drift
1. Any sediment laid down by, or in association with, the activity of glacial ice. The term is often widened to include related submarine and lacustrine deposits. The British Geological Survey has used it to refer to all superficial (i.e. draft) deposits. It was introduced by C. Lyell (1797–1875), who suggested that glacial deposits were laid down by melting icebergs which drifted across an ice-age sea covering Britain. This old term is now largely superseded by more recent classifications.

2. (Instrumental) The change in the output of a recording device due to internal factors. Systematic drift can be compensated for by repeat readings at a base station.

drift The British Geological Survey has used this term to refer to all superficial (i.e. drift) deposits (see drift map). Sometimes the term has been used to describe any sediment laid down by, or in association with, the activity of glacial ice and it is often widened to include related submarine and lacustrine deposits. The word was introduced by C. Lyell (1797–1875), who suggested that glacial deposits were laid down by melting icebergs which drifted across an ice-age sea covering Britain. This old term is now largely superseded by more recent classifications.