Why are the tops of mountains round and the soil often rough, rocky, and thin in many places in the Northeast?

The early settlers abused and overused the land.
Glaciers scoured the landscape, grinding the high places and mixing the soil with rocks.
The Indian population purposely destroyed the countryside when they discovered the white settlers would not leave.
During the past three centuries, the urban dwellers in the area have appropriated the fine soil for the cities. what is 4+2