Mount Desert Island: Shaped by Nature

To do this they first laid down straight lines to guide them and then pounded holes into the granite six to eight inches apart. After all the holes were made iron wedges were pounded between "half rounds" in each hole. The worker would strike each one once then return to hit them again after waiting for a period of time. The longer the worker waited, the straighter the break would be. Eventually the granite would split in a straight line.
Workers would have to be careful to remove the half rounds and wedges before the split to prevent those from being lost. Each worker bought these themselves.