Sorry,I don't want to argue with all of you,and i do not feel the need to defend German marbles,but what i read in previous posts,i can not agree with.
Germany has made many different 2.seam slag type's,you can hardly imagine,regularly i come across new type's 2.seam slags.
Good quality glass and less quality.
Straight lines from seam to seam and swirling lines from seam to seam.
Gaps between the seams and closed seams.
2 seam slags and 1 seam slags.
Hopefully these pic- will give an idea of the different 2.seam slags made in Germany.