All 1879 issues have 7 tail feathers.
1879 would make it a Morgan dollar, which has an eagle on the reverse.
Sorry this isn't a American silver eagle. This is a Morgan silver dollar. The mintmark is located above the DO in DOLLAR on the back of the coin.
An 1879 "Silver Dollar" is a Morgan dollar.
The first silver eagle was made in 1986 not 1879. It's called a MORGAN dollar after the designer George T. Morgan and assuming it's circulated and has no mintmarks, retail value is $17.00-$26.00 the date is very common.
1879 would make it a "Morgan" dollar.
The 1879 Morgan dollar has a diameter of 38.1mm, thickness is 2.4mm.
This link shows a 1879 Morgan Dollar: http://www.coinfacts.com/silver_dollars/morgan_dollars/1879_morgan_dollars/1879_morgan_dollar_obv.jpg
It's a Trade Dollar not a Morgan dollar. If you look at the back of the coin, the phrase "Trade Dollar" is under the eagle. As to value, take it to a coin dealer for an assessment it may not be genuine. The entire series is known to have had copy's and fakes made.
An 1879 S Morgan dollar in MS(Mint State)63 condition is worth somewhere around $64. This is a common date.
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
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.