What is onion skin weathering? And on what kind of rock can you see this weathering?

answer:

Onion-Skin weathering is also known as exfoliation, thermal expansion and insolation weathering. This process often happens in deserts. When the rocks are heated up in the morning, and cools in the night, stress is inserted on the outer layers of the rock.

a characteristic is a deep cut in the earth or left over rock aka till.