Sandstone walls

Sandstone walls are really beautiful, although some of their history is ugly.
They were usually built at the time of the enclosures. Common land was being seized for profitable sheep farming, when most of the sandstone walls around fields were put up. The impact on the rural population at the start of the industrial revolution is still being felt. The current lack of peasant farmers in the UK is one result of our ancestors' having been forced to give up their survival farming plots.
The degree of weathering of stone is an obvious clue to how old they are, although the level of exposure to the elements, to traffic and acid rain can confuse this a bit.
If you look at the craft markings on the stone, you can usually work out how old the walls are. The earliest walls that you can still see a fair number of, especially in West Lancashire, have signs that the stones were cut by hand. They have irregular marks from the tools that were used.
Walls dating from after the start of the Industrial Revolution show the impact of machine tools, often with regular shallow long ridge patterns. Recent walls tend to be smooth and lacking in character. However, any sandstone used to build walls will become mellower and more attractively uneven over time.