The image that I show are the cutlines.
They are a valuable way of getting an ID on many marbles--they are not always true but the vast majority will line up with a certain company.
Patches such as yours are almost always determined by the cutlines.
Swirls and Slags also have a certain way with the cutlines.
The cutlines were made as the glob of glass was cut away from the stream of glass that was pouring out of the furnace--very fast but very determinate as far as vintage marbles go.
I wish that I could add some more info---
Research, Research, Research this is the fun in collecting marbles.
Marble--On!!