Here are a few snippets from that last section:
Although there was no simple all-embracing formulation that writers of the twelfth century could use to label green children from below the earth, diminutive household spirits, beautiful ladies dancing by night in woodland halls, and other fleeting and uncanny creatures, they were clearly considered to belong together and are not merely a category invented by modern historians and scholars. The evidence is that writers like Ralph of Coggeshall and Gervase of Tilbury group their stories about such beings together ... If such beings thus constituted a class, there was still no agreed explanation of their origin and nature ... The minds of the men and women of England in our period thus ahd room for a variety of beings that did not fit neatly into the orthodox and established trio of man, beast, and (good or bad) angel. There was nothing 'popular' about such beliefs, except in the sense that they were widespread ... Strange breeds and spirits were thus just as much at home with the gentry as the peasantry. Similarly, a learned education did not make one less likely to believe in such beings. The clergy was a s deeply enmeshed as the gentry ... The strange creatures that flitted across the borders of the human and the mundane world were not beyond the bounds of possibility. Below the Essex fields, within the Yorkshire barrows, and beyond the Suffolk shore were creatures who lived an alien life of their own.
I'd only add: I'm not sure that these aliens lived their own lives so much as they lived lives of possibility on behalf of those who dreamed them. Among these possibilities was that of an England that did not have to come into being through violent circumscription, a capacious rather than constrictive space that could be a part of an archipelago rather than a pars pro toto.