As the glacier moves over the land, it picks up the easily eroded material available, and works at breaking down the harder rock. Usually, the longer the material has been carried under the grinding action of the underside of a glacier, the smaller it will be when it finally is released by the ice. Till is made of sedimentary materials of many different sizes. Photograph courtesy of John Anderson, Rice University. A large glacial erratic .
Ice is capable of carrying all sizes of material if it is available.
Photograph courtesy of John Anderson, Rice University. As the ice flows over the bedrock , it picks up particles. Bedrock is made up of different components in different areas. In another area, the glaciers may flow over granitic rocks and acquire a granite signature. A glacial geologist can tell where the ice came from by the minerals and rocks in the subglacial till.