I am so late to this but only just recently started more research on the family tree. I have also found Major Arnold & Sarah Chalkley in my tree. They are my 6th great grandparents. Their daughter Sarah Arnold married Edward Roberts etc eventually leading down to me.
My great grandad was the last of that line to be born in Bedfordshire before his parents moved to Yorkshire where I was born, so I've not got much idea of the places in Southern England. I've been searching around for her parents too coming up with William Chalkley & Mary Harmer also. Anymore info on this would be great.

Interesting I have a DNA match on another site their surname Chalkley & still in Hertfordshire, so it's come all the way down the line, they have an extensive tree with William & Mary Harmer too but no Sarah Chalkley. She must be related somehow or I wouldn't be a DNA match, if their tree is correct that is.