Here's how it happens:

* Glacial Erosion: As a glacier moves, it erodes the underlying bedrock and sediment. This erosion can be both abrasive (like sandpaper) and plucking (removing chunks of rock).

* Glacial Deposition: As the glacier melts and retreats, it deposits the eroded material it has been carrying. This material is often deposited in long, teardrop-shaped hills called drumlins.

* Formation: Drumlins form when the glacier encounters a resistant area of bedrock, causing the ice to pile up. The flow of the glacier then shapes the deposited material into a streamlined hill, with the blunt end facing the direction from which the glacier flowed.

So, if you see long, smooth hills that are aligned in a similar direction, it's a good indication that they were formed by glaciers.