they were thought to have drifted in on icebergs. They correctly understood that only ice
could have brought these materials, but not that there were thick ‘rivers’ of ice moving over
the Earth in places where no ice exists today.
Another glacial depositional landform which forms under a glacier by water melting from
the ice is anesker(Figure10.43). These curving ridges of sand are deposited by streams
that run within the ice along the base of the glacier. A normal stream carves its channel
into the ground, forming a ‘V’ shaped channel, with the wide part of the ‘V’ at ground level.
Because the water in this stream moves through the ice, not on the ground, only the deposits
mark where these streams flowed. When the ice melts, the sediments form an upside down
‘V’ on the ground.
Adrumlinis another type of asymmetrical hill that glaciers form but this one is made
of sediments. A drumlin is an upside down teaspoon shaped hill which lines up with the
direction the ice moved. The sediments dropped by the glacier are thought to be formed into
a long narrow hill by the flowing glacier with the gentle sloped end pointing in the direction
of ice flow. Usually drumlins are found in groups called drumlin fields.
Once material has been deposited by the glacier, water melting from the glacier can sort
and retransport these sediments. An important difference between glacial deposits formed
directly from the ice and those that form from glacial meltwater is their degree of sorting.
Ice is capable of carrying a tremendous range of particle sizes, but solid ice does not sort any
of these particles. So when material is dropped as ice melts, you will find very large pieces
jumbled together in an unsorted deposit along with all the other size particles it carried.
A very different situation occurs when running water moves particles. Liquid water cannot
carry the large particles that ice carries. So as water moves through these unsorted deposits,
it will select out only the smaller bits of sand and silt that it can carry. This produces a
sorted deposit of just the sand and smaller particles transported by liquid water. Often these
deposits form layer on layer and show the direction that rivers flowed. These deposits are
calledstratified drift.Often a broad area of stratified drift blankets the region just beyond