In EGLE's book:
VI. ROBERT ELDER,3 (Robert,2 Robert,1) b. 1734, in Hanover township, then Lancaster
             county, Pa.; was twice married. His first wife's name was COLE, and they had one son,
            JOSEPH.
After her death, he removed to Maryland, afterwards returning to his old home
near Harris' Ferry. About 1786, he went to Indiana county, Pa., where he died in 1790. His second
 wife was MARY TAYLOR, who d. April 15, 1813. They had issue:
                     18.    i. James, b. 1763, in Penn'a; m. Martha Robinson.
                     19.   ii. David, b. October 16, 1764, in Maryland; m. Ann Nesbit.
                     20.  iii. Robert, b. 1767; m. Mary Smith.
                     21.   iv. Anne, b. 1770; m. Archibald Marshall.
 

Lee Elder's list, page 5:
SAMUEL ELDER, d. 04-06-1885, Fortress Monroe, Va. Buried Paxtang Cem.
married Elizabeth Garland, she d. 11-19-1890, Cincinnati, Ohio,Buried Paxtang Cem.
He was a Major in 2nd Artillery, US Army.
Elizabeth was from Kenderson, KY.
Samuel's father:
Robert ELDER, b. 1791 married Elizabeth Sherer, buried Paxtang Cem.
Robert died 1827.
Robert's parents:  David Elder married Ann Nesbitt.

Civil War Battle in Florida:
http://extlab1.entnem.ufl.edu/olustee/support_union.html

There's a Colonel Guy V. HENRY in the Civil War from MA,
on the same webpage as a Captain ELDER, of ELDER's HORSE
BATTERY.
    GUY V. HENRY is in my mother's HENRY family book
and now I see where Samuel Sherer ELDER fits into
the ROBERT ELDER list...

Next webpage linked for the Battle in Florida has a good ELDER quote:
http://extlab1.entnem.ufl.edu/olustee/letters/mass-cav.htm
" ....Then, as the case became desperate,
we were placed close to the guns of the one battery
(Elder's horse battery, four Napoleon
guns), which held its own, kept its guns, and
saved the army by allowing our troops to draw out of the trap just as
darkness came on. Darkness alone saved us...."
   For an hour we clung to that battery, with a hail of fire that was
mostly too high.
Twice I thought we should use our sabres, as the yelling devils came
down for those guns.
But Elder (afterwards Grant's chief of artillery) was
fearless, and kept his men at work gloriously.
With black darkness the fighting ceased. The enemy seemed
indisposed to push us. Perhaps Seymour's
ruse of having each regiment give three times three cheers made them
think
we had fresh arrivals of troops...."