here is Wikipedia's definition of sepia toning; Sepia toning
See also: Sepia (color)
The term 'sepia' comes from the name of an artists' pigment made from the Sepia cuttlefish, found in the English Channel, Sepia officinalis, the Common Cuttlefish.
In sepia toning, chemicals convert the metallic silver in the print to a sulfide compound, which is much more resistant to the effects of environmental pollutants such as atmospheric sulfur compounds. This is why many old photographs are sepia toned—those are the ones that have survived until today.[citation needed]
There are three types of sepia toner in modern use;
Sodium sulfide toners - the traditional 'rotten egg' toner;
Thiourea (or 'thiocarbamide') toners - these are odourless and the tone can be varied according to the chemical mixture;
Polysulfide or 'direct' toners - these do not require a bleaching stage.
Except for polysulfide toners, sepia toning is done in three stages. First the print is soaked in a potassium ferricyanide bleach to re-convert the metallic silver to silver halide. The print is washed to remove excess potassium ferricyanide then immersed into a bath of toner, which converts the silver halides to silver sulfide.
Incomplete bleaching creates a multi-toned image with sepia highlights and grey mid-tones and shadows. This is called split toning. The untoned silver in the print can be treated with a different toner, such as gold or selenium.[4]
Sepia-toned images are associated with period photography of the 1800s and "that old-time feel". Many photographs of the American Old West were recorded in sepia tones, a notable example being Edward Weston's photos of Carmel. Consequently, sepia toning has been used in movies as a special effect to evoke nostalgia or the Wild West. For instance, the Kansas scenes in the 1939 movie The Wizard of Oz are rendered in sepia tone, while technicolor takes over in the land of Oz.
NGE
great pictures 
You do have a great eye for your compositions. My personal fav is the 2nd picture. Beautiful depth of field and very well balanced. You always post such nice photographs. Sometimes I wish I lived out west for the beauty, but I think I would be giving up too much history.
