It may be suggested, further, that a four-year course, such as we have seen was customary in many places, might possibly have originated from the custom of cropping the land every year. The difficulties of maintaining the fertility of the land, and of keeping it clean, under perennial crops, might very well have been found insuperable before the introduction of turnip culture, and the natural remedy, suggested by the two-or three-year course in neighbouring parishes, would be a periodic fallow. It is, however, so far as any evidence that can be supplied from the eighteenth and nineteenth centuries goes, equally possible that the four-year course was a modification of the three-year course, or that the two-, three-and four-years systems are all equally ancient; and that the varying customs, not only of systems of tillage, but also of occupation of meadow land and regulation of common of pasture, as found in different parts of the country, have grown up in each district as the result of the inter-action of Keltic, Anglo-Saxon, and Norse tradition. If we take this view, which appears to me antecedently probable, we can see in the Midland or Mercian system a complete blend of Anglo-Saxon and Keltic custom, in which the specific features of both of the original strains are lost, and an intermediate, but perfectly distinct, type of village community resulted. The Wessex system, both in its feature of lot or rotation meadow, and in the customs of individual cultivation of land for common benefit, as in the sowing of clover by each occupier to be fed on by the village flock, compared with the Mercian system, shows a much closer affinity with Keltic run-rig; while the Norfolk customs are quite easily accounted for as the result of a fresh infusion of Teutonic tradition, re-introducing the original one-field system into villages where that system had previously been blended with Keltic custom. CHAPTER XVI. COMMON FIELDS IN NEW ENGLAND. A certain amount of light upon the question when the common field system lost its vitality, its advantages being completely overshadowed by its disadvantages, so that only the obstructive forces which we have considered prevented its disappearance, is furnished by the fact that the original settlers of New England, who presumably derived their ideas of agriculture from the eastern counties of England, reproduced in America a form of the English village community. No doubt their poverty and early difficulties compelled them to revert to a further degree of dependence on mutual help, and so perhaps the form of community which they there established may have been of a more primitive type than that which they had left behind, and allowance must be made for this possibility; and also for the possibility of effects of the sojourn of the Pilgrim Fathers in Holland. The following accounts of the New England common fields are taken from two papers by Mr. Herbert B. Adams:--