[Facts] Re: great grandfather's name
In Dutch 'bergen' is a word meaning 'mountains'.
I also found out that Berg is a first name. I think that it will be connected to Bergan/Bergen.
Berg is a Germanic, male name. It comes from one element: 'berg', meaning 'protection'.
I hope this helped you.
Source: Schaar, J. van der, Prisma voornamen, Het Spectrum 2002 Utrecht