What does it mean to dash out someone's brains?

I'm doing a report on Hannah Dustin. The story I found online says, "Finding that carrying the baby was making it hard for Mrs.Neff to keep up, one of the Indians seized it from her, and before its mother's horrified eyes dashed out its brains against an apple tree." What does that mean? What exactly did the Indian do to the baby? Did they just smash the baby's head on a tree? Or does that mean something else?