I'm having a and can't seem to find out the meaning of this symbol in the picture which is from a 1870's historical map, which is a plus sign inside a circle.
If you're close enough to one of the areas you're asking about, you might go check it out. You may find the areas in question are smaller family cemeteries.
Just to throw this out there...
From the late 1700's (1790's) to the late 1800's the + sign represented a church.
The circle around it may indicate something "about" the church.
But ?
I can recall from my map reading classes that the map maker is responsible for making a legon that should depict what the symbols on his map represent. Here's some of the symbols that the USGS uses on their topographical maps, the X is a mining prospect and the O a landmark: