Boulder clay in the context of Till

In geology, drift is a name for all sediment (clay, silt, sand, gravel, boulders) transported by a glacier and deposited directly by or from the ice, or by glacial meltwater. Drift is often subdivided into unstratified (unsorted) drift (glacial till) that forms moraines and stratified drift (glaciolacustrine and fluvioglacial sediments) that accumulates as stratified and sorted sediments in the form of outwash plains, eskers, kames, varves, and so forth. The term drift clay is a synonym for boulder clay. Both are archaic terms for glacial tills with a fine-grained matrix.

In the United Kingdom, drift is also applied as a general term for all surficial, unconsolidated, rock debris and sediment that is moved from one place to accumulate in another and mapped separately or otherwise differentiated from underlying bedrock. In this usage, drift includes a wide variety of deposits, e.g. loess, glacial till, river deposits, colluvium, and so forth, of Quaternary age. However, this term is most commonly used to specifically describe glacial deposits.

Derrywarragh Island is a boulder clay island on Lough Neagh, Northern Ireland. It is linked by a bridge to Maghery, County Armagh. The island is approximately 13 kilometres (8 mi) northwest of Portadown. Most of the island is wet grassland. There are also areas of wet woodland, marshes and swamps. The island is also regularly the home of wintering and breeding birds.

Diluvium is an archaic term applied during the 1800s to widespread surficial deposits of sediments that could not be explained by the historic action of rivers and seas. Diluvium was initially argued to have been deposited by the action of extraordinary floods of vast extent, specifically the Noachian Flood.

In 1822 and 1823, William Buckland published the term diluvium in his monograph Reliquiae Diluvianae and in G. A. Mantel’s monograph about the geology and paleontology of the county of Sussex. Buckland divided the surficial deposits overlying regional bedrock into diluvium and alluvium. Diluvium was defined as sediments, including boulder clays, laid down by geological processes that could no longer be observed. Buckland considered the Noachian Flood to be one of these geological processes no longer in existence. "Diluvium" eventually became widely used in Europe, and was retained even into the 20th century for glacial deposits, long after the Noachian Flood explanation was quietly abandoned. Buckland defined alluvium as surficial sediments laid down by processes currently active and observable, such as those associated with existing streams and coastal environments. In Germany, diluvium was also known as the Eiszeit or Glazialzeit and alluvium was known as the Postglazialzeit. Both were grouped together in the Quartär, or Quartäre Eiszeitalter, which is equivalent to the Quaternary Period.