That almost looks like the matting Greener used on many martini actions. If that is a damascus pattern, I have never seen one like it before. Thanks for posting it.
Definitely some form of matting or roll-graving; and not a good look. Maybe Pieper's idea
J. Manton & Co.
Wilmot Gun Co.
All I see is rib matting on all the flats at the breech. No damascus pattern visible. Very cheap (Belgium?) gun. This is an example of the multitude of guns sold to the colonies and America around the turn of the century.