Thanks very much folks. Not having the physical object is making this a bit more difficult than I had hoped.
Regarding the older woman... I saw a picture of her in her 90s (not a very goodpicture) but could agree that this is about 20 years before that... 1890s makes sense to me. I have other pictures that I know are 1885 - 1890 in similar mount. The black dress is indeed mourning garb. Her husband died in 1879. She wore black every day thereafter. This lady lived in rural New Brunswick Canada.
The younger lady was born in 1889 and I'm guessing that hse is about 20 years old. But I'm often a lousy guesser of age. I don't know the circumstances for her being so well groomed and fancy dressed. She lived in Bangor Maine. I know she married about that age but don't know if htat is in any way connected with this photo or not.
I'm going to try to obtain more information about the markings on the mount, if possible.
Thanks again... you insights and suggestions are very much appreciated!