I quite agree with your correspondent BURIENSIS as to the origin of the
title given to various old oak trees in different parts of the country.
These trees were no doubt selected on account of either their position,
age, or size, as places of assembly for the early Christians, and from
them the "Gospel" was, probably, first preached in their respective
neighbourhoods.
That these trees were connected with religious observances is evident
from the following lines in the 502nd poem of Herrick's _Hesperides_.
The poem is addressed "To Anthea:"--
----"Dearest, bury me
Under that holy oak, or _Gospel Tree_;
Where, though thou see'st not, thou may'st think upon
Me, when thou yearly go'st procession."