Thamisine Rosevear Grose was a sister to my great grandfather, Joseph Rosevear. Thamisine married Joseph Grose in 1852, probably at Luxulyan, Cornwall, England. She was living at Kelton, Utah,USA, where she died in 1873.
What kind of relationship do you have to Thamisine that she was included in your family tree? I noticed you also have an interest in the "Mark" surname. Thamisine and Joseph Rosevear had a sister, Ann, who married Nicholas Mark, also from Luxulyan, and went to Utah.
Hope this information helps.