Very nice marbles. The white one is an excellent example. What size?
They are melted pontils.
The two showing the most purple/white appear to be from Navarre, Ohio, which was one location of James Leighton's marble making plants. The colors and the "looping" out of the pontil are charactistics of marbles coming from this plant. I would say it is very possible for the white one comming from this location also.
thanks.