The unsorted sediment deposited directly by a glacier is called till. It forms when moving ice erodes, carries, and eventually releases a chaotic mixture of material ranging from fine clay and silt to sand, gravel, cobbles, and large boulders.
Unlike sediment transported by ordinary rivers, till is typically unstratified and poorly sorted because flowing ice does not separate particles by size in the same way water does. Clasts in till may be angular, scratched, polished, or striated, recording the abrasion that occurred as rocks were dragged beneath the glacier.
Till can accumulate beneath ice as ground moraine or appear in terminal, lateral, and medial moraines. It may also help form landforms such as drumlins. Meltwater can later rework till into better-sorted deposits called outwash, which is why till and outwash are related but not interchangeable. If buried and cemented into rock, till becomes tillite.