Glacial sediment is extremely heterogeneous. It typically displays great lateral and vertical variations in thickness, composition, texture, sedimentary structures, and mode of origin. Glacial sediment can be divided in two general categories: till and stratified sediment.

Till is defined as " a sediment that has been transported and is subsequently deposited by or from glacier ice, with little or no sorting by water". It is material that was released from glacier ice usually by melting and was deposited without significant transportation or sorting due to water or gravity movements.

Several general observations may be given about the occurrence of till

• Deposition of till must postdate erosion or deformation of the underlying substratum; most till was probably deposited late in the glacial cycle; the law of superposition applies to till as well as to other glacial sediment.
• Till is a mixture of anything and everything over which the ice moved, including: bedrock, older till and sediment, weathered material, soil, plant fragments, and animal remains. Till is dominated at any spot by material of local origin; the content of local material generally decreases upward in a till sequence
• Multiple till layers are common in the outer zones of glaciation. However, owing to different mechanisms of till deposition and changing ice movements, separate tills do not always indicate separate glaciations. Periods of glacier withdrawal are shown by buried soil, peat, weathered zones, fossils, permafrost features, etc