Shield (geology)

"[3] A shield is that part of the continental crust in which these usually Precambrian basement rocks crop out extensively at the surface.

[6] The landforms and shallow deposits of northern shields that have been subject to Quaternary glaciation and periglaciation are distinct from those found closer to the equator.

[5][7] Shield surfaces exposed to sub-tropical and tropical climate for long enough time can end up being silicified, becoming hard and extremely difficult to erode.

[7][8] In the Fennoscandian Shield, average glacier erosion during the Quaternary has amounted to tens of meters, though this was not evenly distributed.

[8] For glacier erosion to be effective in shields, a long "preparation period" of weathering under non-glacial conditions may be a requirement.