Answer :
When a glacier retreats, it can leave behind cobbles or boulders. Hence, boulders is the answer.
What is Boulder?
A boulder is a rock piece larger than 25.6 centimeters (10.1 in) in diameter in geology. Cobbles and pebbles are terms for smaller bits. Some boulders are so small that they can be moved or rolled by hand, but some are incredibly large. Generally speaking, a boulder is anything that a person cannot move. Smaller boulders are more commonly referred to as rocks or stones. The Middle English term bulderston or the Swedish word bullersten is where the word boulder first appeared.
Some sedimentary rocks, such coarse conglomerate and boulder clay, include clasts the size of boulders. Bouldering is the term for climbing huge rocks.
To know more about rocks refer:
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