Here's why:
* Glacial till is unsorted, angular, and often contains a mixture of rock types and sizes. This is because glaciers act like giant bulldozers, scraping and grinding the bedrock as they move. They pick up a wide range of rock fragments, from fine clay to large boulders, and deposit them in a jumbled mass.
Other rock materials might be found in areas affected by glaciers, but they are less likely to be directly transported by the glacier itself:
* Outwash is sorted and rounded material that was deposited by meltwater from a glacier. It's found in areas surrounding glacial valleys.
* Erratics are large boulders that have been transported far from their source by glaciers. They are often found perched on hillsides or in unexpected locations.
* Glaciofluvial deposits are sediments deposited by meltwater streams flowing from glaciers. They are typically well-sorted and layered.
Therefore, the presence of glacial till is a strong indicator that the area was once glaciated.
