In general $25.00-$35.00, but it also depends on the condition of the coin and if it has any mintmarks. Look at it again and post new question with more info.
Mintmarks are on the reverse above the letters DO in dollar.
An 1879 "Silver Dollar" is a Morgan dollar.
An 1879 S Morgan dollar in MS(Mint State)63 condition is worth somewhere around $64. This is a common date.
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.
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.
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
Assuming the coin is circulated and has no mintmark, the 1879 Morgan is a high mintage common date, retail values are $17.00-$26.00
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.
1879 would make it a "Morgan" dollar.
1879 S is not a rare date for Morgan dollars. On average if they are in circulated condition they are worth $16.50.
Assuming no mintmarks, circulated Morgan dollars from 1879 are worth $17.00-$26.00 depending on condition.
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.
Retail for circulated coins is $17.00-$26.00 depending on the grade.