Terrific info Isabel and wonderful family anecdotes Tony. From this it would appear that the family were at Nether Careston, then for whatever reason didn't extend their lease and moved away 1780-1800.
There is lots on the net about Nether Careston. Plan of the farm of Nether Careston
http://www.scotlandsplaces.gov.uk/record/nrs/RHP780/plan-farm-nether-careston/nrsMI's including (34) and (35) Mitchells and (36) George Mitchells
http://www.ancestor.abel.co.uk/Angus/Careston.htmlThis website also has parish maps of Kincardineshire and Angus (Forfarshire)
Angus Archives have the rental of the estate of Careston 1724-1740 including 40 farms and their tenants.
Familysearch has the Careston registers batch C11277-2
https://familysearch.org/search/record/results?count=20&query=%2Bgivenname%3Ageorge~%20%2Bsurname%3Amitchel*~%20%2Bbatch_number%3AC11277-2
In the 17th century Careston was in the parish of Brechin familysearch batch C11275-2 has three George Mitchells to choose from 4/7/1707 son of Geo and Margaret Bean, 25/1/1719 son of James and Margaret Nepper and 28/8/1720 son of Geo and Elizabeth Watt.
If you have the time and inclination it could be interesting building Careston Mitchell families and bringing them forwards.
Gossesslie Farm is in the parish of Marykirk hence George and Elspet Mitchell's children being bpt there. I think Isabel H could well be right in that Elspet and Isab. are one and the same person. This makes me wonder whether Margaret could possibly be a mistranscription for Elspet? Could be worth getting the original entry in the register checked.
I read that "Lizzie Lindsay" was popular in the 18th century.
Do you think this is where George Lyall got his name from? "A grey granite stone commemorates the Rev. David Lyell and his wife the Hon. Catherine Arbuthnott." Also " The story goes that the farmer Mr. Mitchell had difficulty in persuading his men to work the machine for it was thought impious to use the "Devil's Wind."
http://junkinsfamilyassociation.wikidot.com/church-parish-careston-scotlandHave fun and hope these links work!