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Till

Till

[til]
Eulenspiegel, Till [Ger.,=owl-mirror, hence English Owlglass], a north German peasant clown of the 14th cent. who was immortalized in chapbooks describing his practical jokes on clerics and townsfolk. The first Till chapbook (c.1500) was probably in Saxon, but the story it told spread all over Europe and North Britain. Till is the hero of a tone poem by Richard Strauss and of many novels, poems, and stories. Tyll Ulenspiegel is one of the variant spellings.

See K. R. H. MacKenzie's adaptation in English, Master Tyll Owlglass (1890).

till: see drift.

In geology, the unsorted material deposited directly by glacial ice and showing no stratification. Till is sometimes called boulder clay because it is composed of clay, boulders of intermediate size, or both. The rock fragments are usually angular and sharp rather than rounded, because they are deposited from ice and have undergone little water transport. The pebbles and boulders may be faceted and striated from grinding while lodged in the glacier.

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or till-less agriculture

Cultivation technique in which the soil is disturbed only along the slit or hole into which seeds are planted. Reserved detritus from previous crops covers and protects the seedbed. Primary benefits are a decreased rate of soil erosion; reduced need for equipment, fuel, and fertilizer; and significantly less time required for tending crops. The method also improves soil-aggregate formation, microbial activity in the soil, and water infiltration and storage. Conventional tillage controls weed growth by plowing and cultivating, but no-till farming selectively uses herbicides to kill weeds and the remains of the previous crop. No-till farming is one of several primitive farming methods revived as conservation measures in the 20th century.

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German peasant trickster of folk and literary tales. The historical Till is said to have died in 1350; anecdotes associated with his name were printed circa 1500 in Low German and from 1515 in High German. In the tales the stupid yet cunning peasant demonstrates his superiority to the narrow, dishonest, condescending townsmen, as well as to the clergy and nobility. The tales were translated into Dutch and English (circa 1520), French (1532), and Latin (1558).

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Till is unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. It may vary from clays to mixtures of clay, sand, gravel and boulders. Clay in till may form in spherical shapes called till balls. If a till ball rolls around in a stream, it may pick up rocks from the streambed and become covered by rocks; thence it is known as an armored till ball.

Till is deposited at the terminal moraine, along the lateral and medial moraines and in the ground moraine of a glacier. As a glacier melts, especially a continental glacier, large amounts of till are washed away and deposited as outwash in sandurs by the rivers flowing from the glacier and as varves in any proglacial lakes which may form. Till may contain alluvial deposits of gems or other valuable ore minerals picked up by the glacier during its advance, for example the diamonds found in Wisconsin, Indiana, and Canada. Prospectors use trace minerals in tills as clues to follow the glacier upstream to find kimberlite diamond deposits and other types of ore deposits.

Tillite

In cases where till has been indurated or lithified by subsequent burial into solid rock, it is known as the sedimentary rock tillite. Matching beds of ancient tillites on opposite sides of the south Atlantic Ocean provided early evidence for continental drift. The same tillites also provided the key evidence for the Precambrian Snowball Earth glaciation event.

Types of till

There are various types of classifying tills:

  • primary deposits – these were laid down directly by glacier action
  • secondary deposits – these have undergone reworking (e.g. fluvial transport, erosion, etc)

Traditionally (e.g. Dreimanis, 1988) a further set of divisions has been made to primary deposits, based upon the method of deposition.

  • Lodgement tills – sediment which has been deposited by plastering of glacial debris from a sliding glacier bed.
  • Deformation tills – Sediment which has been disaggregated and (usually) homogenised by shearing in the sub glacial deformed layer.
  • Melt out tills – Released by melting of stagnant or slowly moving debris-rich glacier ice and deposited without subsequent transport or deformation. Split up into sub glacial melt out till (melting of debris rich ice at the bottom of the glacier) and supraglacial melt-out till (melting of ice on the glacier surface).
  • Sublimation till – similar to melt out till, except the ice is lost through sublimation rather than melt. Often occurs only in extremely cold and arid conditions, mainly in Antarctica.

Van der Meer et al. 2003 have suggested that these till classifications are outdated and should instead be replaced with only one classification, that of deformation till. The reasons behind this are largely down to the difficulties in accurately classifying different tills, which are often classified based on inferences of the physical setting of the till rather than till fabric or particle size analysis data.

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References

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