@vickyveritas
My geochemist partner looked at the #Blackstone in her long ago dissertation, looking at the clearly #mafic #greenschist facies, which may be ocean basin (maybe a mantle plume interacting), with some odd alkaline basalts, analogous to, maybe, #Iceland. Maybe it was oceanic crust between Avalonia and Gondwana. She thinks this tuff is mafic, based on setting, but she hasn’t put it in front of polarizing filters beneath a microscope. She wants to. Much work to do.

Where is Babel Rock?

The #USGS #BlueHills #quad #bedrock map and a #Quincy #Massachusetts #historical #map show Babel Rock overlooks a pond from just north of a bend in #Wampatuck Rd. I have been on that rock, and it's #diabase, a #mafic #intrusion into the Quincy #pluton. But the USGS #topographic quad & derivatives e.g. #GoogleEarth show it adjacent to the #BunkerHill #quarry (source of the #granite for the monument in #Boston).

Should a correction be proposed to USGS? Advice welcomed.