In any farming system the relation between crops and animals was crucial. As a source of food, animals normally make less efflcient use of the land than do cereals. But when manure from cattle and sheep was the main fertilizer they were indispensable. The bitter conRict between primarily arable farming and largescale pasture had gone on for centuries and was still familiar in many areas. Which one predominated depended not only on the quality of the land but on a complex interplay of prices, power, and habit. There were large regions, and also small areas, where one type of agriculture was naturally more successful than another: England had its 'highland zone' where cattle and sheep occupied most of the land and its lowlands where cereals were combined with fewer animaIs; but within them districts of dairying, stock-fattening, sheep with com, woodland and fen were intermingled. Wool still brought wealth; but the days of everexpanding sheep-farming were over. In Spain the Mesta, though it still controlled something like two million sheep moving between north and south, was no longer making large profits . Spanish sheep-farming was as much in decline as the rest of its agriculture; but there, as in northern England and most other hili country, falling cereal prices later in the century made sheep comparatively profitable again.