Agriculture in prehistoric Scotland includes all forms of farm production in the modern boundaries of Scotland before the beginning of the early historic era. Scotland has between a fifth and a sixth of the arable or good pastoral land of England and Wales, mostly in the south and east. Heavy rainfall encouraged the spread of acidic blanket peat bog, which with wind and salt spray, made most of the western islands treeless. Hills, mountains, quicksands and marshes made internal communication and agriculture difficult.