Stamboom is family tree or pedigree or whatever. This is basically a guy in the Netherlands doing what I'm doing here in the US: assembling a family tree online. And he's got my paternal grandmother's maternal grandparents.
I think that's right: it's my father's mother (that's Bertha)'s mother (Hendriena/Hendrina/Wilhelmina/who knows)'s parents (Dammis Poldervaart -- misspelled OF COURSE in my paper geneaology) and Pietertje Dijkman. The glory of knowing a little bit of Dutch is I quite quickly realized that Dammis was not spelled Dammes, which led me to this.
Sweet! The dates match up just fine, however this guy's tree does not go down my path, so I'll have to keep looking.