Final answer:
Glacial features such as erratics, dropstones, tillite, and polished and scratched bedrock provide evidence for the past presence of glaciers. Erratics and dropstones are rocks carried by glaciers from distant regions, tillite is the lithified form of glacial till, and polished bedrock shows the direction of glacial movement.
Step-by-step explanation:
Matching the feature with its description and how it may indicate the past presence of glaciers involves understanding various geological formations and their characteristics. Here are the matches for the given features:
- a- Erratic: An erratic is a large rock that has been transported and deposited by a glacier, often found resting in an area of completely different rock type. Its presence suggests that glaciers have moved through the area, carrying rocks from distant regions.
- b- Dropstone: A dropstone is a rock that has been released from melting icebergs into fine sediment, creating a disruption in the layering. Finding a dropstone within sediments can be an indication of glacial action in the past, especially within marine environments.
- c- Tillite: Tillite is the lithified version of till, which is an unsorted mixture of rock material deposited directly by a melting glacier. The presence of tillite in the geological record signifies that the area was once covered by glaciers.
- d- Polished and scratched bedrock: Glaciers can polish and scratch the surface of bedrock as they move. These striations are evidence of the direction and movement of ice across the landscape, indicating former glacial presence.