^
Sepia tone is more of a brown/tan color. As with any toning process, the silver in the b&w print is replaced with or converted to another chemical. I forget the exact reason why the brown coloration is called sepia - something to do with the source of the chemicals used to convert the silver.
If the prints you have are about 8x10 inches in size, then they are most likely what is known as a "contact print". Contact prints are created by physically placing the image source directly on top of the photgraphic print paper and then exposing the paper to light (in the case of film negatives a piece of glass would be utilized to press the negative flat against the paper, in the case of a glass negative plate, as you have, this is not necessary).
By eliminating the optics of the enlarger, uneven lighting of the negative, human focusing errors, the possibility of an enlarger bed (where you put the paper) being out of alignment to the projection head, etc... this contact print process yields the absolute highest level of detail and clarity possible for the source image.
Not to mention that the old glass plate negatives have a very unique look to them due to the emulsions and chemical processes used and the extremely long exposure times necessary to take the photgraph.