Leo,
From _The Life of Charles Carroll of Carrollton, 1737-1832 With His Correspondence and Public Papers_ Kate Mason Rowland, vol 2, 1898,
Appendix D, 438-39
Mary Carroll, b. Sept. 2, 1770, m. Richard Caton, son of Richard Caton, of Liverpool, Nov. 1786
1. Mary Caton, m. (1) Robert Patterson, m. (2) the Marquis of Wellesley,
dsp. 1853
2. Elizabeth Caton, m. Baron Stafford, dsp. Oct. 29, 1862
3. Louisa Katherine Caton, m. (1) Col Sir Felton Bathurst Hervey,
m. (2) Francis Osborne, 7th Duke of Leeds, dsp. April 8, 1874
4. Emily Caton, m. John McTavish, British consul to Baltimore
A. Charles Carroll McTavish, b. Jan. 18, 1818, m. Marcella Scott
B. Richard Caton McTavish, b. March 24, 1821
C. Mary Wellesley McTavish, b. Nov. 21, 1825, m. ----- Howard,
son of the Earl of Carlisle
D. Alexander Simon McTavish, b. April 28, 1829, m. Ella Gilmor
According to Burke's Peerage, 4C is Mary Wellesley M'Tavish, Genealogics I00253658
This eliminates a descent from this family for Thomas Riley Marshall, Woodrow Wilson's vice-president. Apparently the late 19th century Wabash Co., Indiana biographical source indicating that was the case is another example to add to the the list of many spurious connections found in such (late 19th century American county biographical) sources.
Marc