ASSARTING AND THE GROWTH OF THE OPEN FIELDS
C ENTRAL and eastern Yorkshire offers a uniquely suitable field for the study of certain problems of twelfthand thirteenth-century agrarian history. The basin of the Ouse, as opposed to the moors of the west and north-east, forms part of the central and eastern English plain; and of the whole region treated in the classical accounts of medieval agrarian history it is, perhaps, the only part which has not been subjected to detailed study. There is a special affinity between the plain of Yorkshire and the region between Welland and Trent ;2 that the rural organisation of Yorkshire after the Conquest has not been studied in conjunction with that of the central Danelaw is due to an event which modified, temporarily or perhaps permanently, the development of the northern district.a The devastation of io69, more extensive in some districts than in others, left about half the Yorkshire plain entirely waste in io86, and had evidently affected many districts in which the Domesday commissioners found some surviving population. There can be no doubt of the intensity and lasting effects of the devastation. In many vills, seventeen years later, no population was recorded, and no income even from woods or rough pasture ; over large parts of Yorkshire the cultivation of the soil was entirely suspended, perhaps for a generation or longer.4 It is, therefore, reasonable to look for the mature post-Conquest development of Yorkshire at a somewhat later date than for that of the region illustrated by Danelam Charters, and to place it in the thirteenth and -perhaps the late twelfth century. The evidence for this period consists chiefly of some thousands of charters surviving in various forms; and with the methods of using charter material elaborated by Professor Stenton the reader must here be assumed to be familiar. I wish to use this material at present only in so far as it relates to the distribution