The usually thin till layer laid down by a retreating glacier is called ground moraine.

Here's why:

* Till is unsorted, unstratified sediment deposited directly by glacial ice.

* Ground moraine forms when a glacier retreats, leaving behind a relatively thin layer of till spread across the ground. This layer is often uneven and can contain a variety of rock sizes, from boulders to fine clay.

Other types of moraines, such as terminal moraines and lateral moraines, are typically thicker and more prominent.