An 1879 "Silver Dollar" is a Morgan dollar.
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.
A certified example of the Philadelphia issue 1879 Morgan in MS-66 has a average retail value of $2,750.00
No collection value but is has a scrap silver value of about 10 bucks.
The 1879 Morgan dollar has a diameter of 38.1mm, thickness is 2.4mm.
The 1879 Morgan dollar is not scarce or rare, assuming it's circulated and has no mintmark, average retail values are $26.00 to $32.00 depending on how much wear the coin has.
The 1879 Morgan dollar is not scarce or rare, assuming it's circulated and has no mintmark, average retail values are $30.00 to $41.00 depending on how much wear the coin has.
Susan B Anthony dollars were not made in 1879. You are probably confusing it with Morgan silver dollars.
Assuming the coin is circulated and has no mintmark, the 1879 Morgan is a high mintage common date coin, retail values are $33.00-$41.00.
This link shows a 1879 Morgan Dollar: http://www.coinfacts.com/silver_dollars/morgan_dollars/1879_morgan_dollars/1879_morgan_dollar_obv.jpg