The Denver Mint opened in 1906. You may be looking at an O mint mark from the New Orleans Mint which operated until 1909.
There's more information at the Related Question.
August 2011>> As of August 2011 the value of a 1887 US dollar graded MS-63 is $73.
1887 is a common date Morgan retail values are $17.00-$26.00 for circulated coins. Uncirculated start at $30.00
Assuming no mint marks value is $20.00 in VF-20 to $40.00 in MS-60
A real silver dollar has a $25.00 value just for the silver.
what is the current value of an 1878 silver dollar
Sorry no US silver dollar coins dated 1826
The US never printed 100 dollar silver certificates with this date.
No US silver dollars were made after 1935, look at the back of the coin for 'Half Dollar'.
current silver troy ounce value
Value is for the silver about $2.50
20,000
Zero