An 1879 "Silver Dollar" is a Morgan dollar.
The 1879 US silver dollar is composed of 90% silver and 10% copper.
No collection value but is has a scrap silver value of about 10 bucks.
Peace dollars were made from 1921 to 1935. An 1879 silver dollar is called a Morgan dollar after its designer George T. Morgan. There's more information at the Related Question
1879 would make it a "Morgan" dollar.
The value for an 1879P morgan silver dollar, uncirculated, is about $45 (Red Book) price. If you have any Morgan's that have mintmark, CC, Carson City, the value goes up.
The 1879 Morgan dollar has a diameter of 38.1mm, thickness is 2.4mm.
Susan B Anthony dollars were not made in 1879. You are probably confusing it with Morgan silver dollars.
Current retail values are $17.00-$26.00 for circulated coins 1879 is a common date for Morgans