these large rocks are a different type of rock than the bedrock in that area, they are called
glacial erratics(Figure10.42). Scientists know only ice could carry these large boulders
great distances. The largest glacial erratic, called Big Rock found in Alberta, Canada weighs
thousands of tons!
Figure 10.42: A large boulder dropped by a glacier is called a glacial erratic. ( 31 )Sometimes long ridges of rock are deposited at the furthest point that the glacier reached.
These are called terminal andend moraines.Just as the conveyor belt at the grocery store
moves your groceries to the end of the counter, a glacier transports rock and sediment while
it flows. If you couldn’t stop the conveyor belt at the grocery store, you would end up with
a big jumbled pile of food at the end of the counter. An end moraine is a little bit like that.
Whatever the glacier has been carrying, all gets left behind in a pile as the ice melts away.
Geologists study these materials to figure out how far glaciers once extended and they can
also figure out how long it took them to melt away. Long Island in New York was formed by
two glacial end moraines. The end moraine that formed this pile of rock and stone deposited
by glaciers extends all the way out to Cape Cod, Massachusetts.
Even while a glacier is flowing slowly downhill, it deposits a layer of sediment underneath
the glacier, which scientists callground moraine. This layer of sediment makes a thick
layer of unsorted sediment under the glacier that fills in low spots and evens out higher
areas. Ground moraine is an important contribution to the fertile transported soils in many
regions. Scientists knew that all these rocks and thick soils came from somewhere else but
for a while they did not know that they came from glacial ice. This is easy to understand
because the ice is not there today. Many scientists thought the big rocks looked like they had
been dropped there and they thought maybe icebergs carried by a huge flood had brought
themthere. Becauseof thisearly hypothesis, lotsof glacialdeposits arecalled ‘drift’, because