I believe there is an ERROR in this LINEAGE.
Gilbert Purvis' son John married Sarah McMillian and that was his Only wife.
1850 CENSUS: Chesterfield District, SC, Line 7, Family/Dwelling 82/82, Page 104B, GS Film #444814. John PERVIS, age 68, Farmer, born in SC; his wife, Sarah [McMillian] PURVIS, age 65; Mary Ann Dickson, age 37, daughter; John C. PERVIS, age 31, Farmer; Alexander PERVIS, age 22; Sarah DICKSON, age 13; Laura DICKSON, age 11; Hariette DICKSON, age 9; Samuel DICKSON, age 7; Mary A. L. DICKSON, age 5.
Revolutionary War Pension Application of James McMillian with sworn affidavit of John Purvis and Sarah [McMillian] Purvis in 1851-1852. Pension #W-9559.
If Clemens Purvis parent were John & Mary Purvis (MS) then I don't believe they are descendants of Gilbert.