Not quite what you are searching for by have (with help of an online tree) found a family connection between Robert Glass & Henry Matier- they were 1st cousins!
___ Glass
1. Elizabeth Glass (1776-1831) m. Robert Matier
1. Henry Matier (1822-1891) m. Maria L. Burrowes- family
2. Robert Glass (1789-1872) m. Martha
1. Robert Glass (1838-1889) m. Sarah Jane Brown- family
Back to search for descendants of Robert Glass-
No clues in his obituary, although seems strange that he's buried alone in plot.
Belfast Newsletter, 15 Mar.1887: GLASS- March 14, at Ulsterville Avenue, Belfast, Robert Glass, aged 53 years. His remains will be removed for interment in the Borough Cemetery, to-morrow (Wednesday) morning at half-past nine o’clock.Son Robert Glass was alive in 1895 (administering father's estate) but I still can't find any trace of him after that. 1895- Robert Glass of 14 Posnett-street Belfast Merchants' Assistant the Son
Son John Birch Glass-
1918 directory- Glass, J. B., tea agent, 81a Victoria Street
http://www.lennonwylie.co.uk/alphanames1918FG.htm (81a Victoria St.) McCoull, William, and Glass, J. B., tea agents) 1924- same; 1932- Wm McCoull, tea agent