Ach, a megalithic desert it may be (though we've got some of the best puddin'stones in the country ;-) What is striking, as we've been driving around, is the amazing (sacred?) site continuity that you seem to get here. Again and again, when visiting churches, we've seen a site that's A) on slightly raised ground and near a spring or stream. B) Church walls built mainly from nodules of flint and/or larger puddingstones but also interspersed with a course or two of Roman bricks. C) One or two much larger sarsens or puddingstones seemingly symbolically placed close to, but not actually in the foundations (found another example of this at Little Baddow church a few weeks ago).
In other words, the sequence at these sites seems to be (sacred) site close to water - remains of stone circle - Roman habitation - Anglo-Saxon and then a Norman use of building materials from any previous on-site structures.
PS On a personal note, Moss and I are happy to announce that we're now a couple :-) Thanks to TMA and our friends here for bringing us together.