By 1100 it is possible that Cornish in east Cornwall was already beginning to give way to English. A linguistic border (or isogloss) had already been established within the territory, dividing Cornish-speaking communities in the majority of the land area from English to the north of the River Ottery and west of the Tamar at Calstock and parishes to the south.
This can be seen in the absence of tre- names in those two areas, as illustrated by Oliver Padel’s map of tre- names.
If we compare the presence of English names for ‘place’ (ton, ham, worth and cot) and the ubiquitous Cornish tre- (homestead, farmstead, hamlet) the districts of early use of English become clear.
It’s possible that the language shift in the north accompanied or occurred soon after the rampages of Wessex’s King Egbert in the early ninth century, with the more southerly incursion coming somewhat later. The older English elements of ham, worth and cott, along with others such as stow, are concentrated in the two districts mentioned. If so, the placename evidence could suggest a fairly stable position for a couple of centuries, perhaps until the Norman conquest of Cornwall in 1070 heralded a period of little understood change on the ground. Many of the other parishes with English-named places in the 1300s included variants of Newton. These were more likely to be new settlements associated with the later expansion of English speaking westwards in the 1100s and 1200s.
Cornish studies resources 