Garnier was probably French and possibly connected with Victor De Grailly, who copied many of William Bartlett’s engravings. The three known paintings by Garnier are of Bartlett scenes, two of which were exhibited at the Leonard Auction Rooms in 1865.
The New Hampshire Historical Society has an oil painting by Garnier, c. 1845, entitled Mount Jefferson from Mount Washington (after Bartlett), 21 x 18 inches.
Reference
New Hampshire Scenery