Marilyn,
I apologize that I did not notice that you said it was a rifle in your title.
That being said, count the number of bands on the forestock that holds the barrel to the forestock. Are there 2 or 3?
Plus, is there a thick metal stub under the end of the barrel? this is referred to as a stud for a bayonet.
On the lockplate (the metal plate where the hammer is attached) besides Tower, is there a date and is there a crown & V.R.?
If it is not a flintlock (which indeed would most likely pre date the Civil War), it might possibly be an Enfield/Tower short rifle. At the beginning of the Civil War, there were a lot of foreign arms imported for U.S. troops.
The Enfield was a fine weapon & was the standard firearm of the English army. adopted in 1853.
Anyway, if you can answer my questions plus whether it is is flintlock or percussion, I may be able to define more closely what you have. It would help to see some close up pictures of the markings & overall picture of the weapon, which could be more definitive.