Thank you for that. I suspected that this must have been Margaret Cavendish's illegitimate son who is with his grandfather Thomas Cavendish at Ballaterson at the 1881 census (Margaret having died in 1868). Margaret & family were still in Jurby at the 1861 census, and would only have inherited Ballaterson in 1865.

1865 Aug 13th no.668 p.84 Jurby
John Robert, illegit son of Margaret Cavendish, Jurby, farmer's daughter;

(1881) Ballatesson, Ballaugh RG11/5598 f89 p2
Thomas Cavendish - H - wid - 61 - Farmer, 110 acres - Michael
Thomas “ - s - un - 35 - Farmer's son - Jurby
John “ - s - un - 33 - Farmer's son - “
William “ - s - un - 24 - Tailor - “
Edward “ - s - un - 22 - Farmer's son - "
Mary A. " - d - un - 40 - "
Elinor S. “ - d - un - 20 - “
Catharine J “- g.dau - un - 16 - “
John R. Dugdale - g.son - un - 14 - “
Elinor E. Brew - g.dau - un - 6 - Ballaugh

Seeing 'Ballaterson' on the Burial record makes it seem more likely that this is indeed the burial of Margaret's son. Thank you again.