Made by an unknown maker in the veronica pattern, ca. 1860-1865.
This is known as a "Pattern Under Glass" lamp because the prism pattern is on the inside of the font and the outside is smooth. A pattern on a plunger was pressed into the glass in a smooth mold. The font was then removed from the mold and skillfully drawn into the collar.
The font is held by a fancy brass stem and marble base. Height 9 1/2" to top of brass collar. Burner is #1 size.
Reference "Oil Lamps", first book by Catherine M. V. Thuro, pages 150, 160.