The Bellingham Conglomerate is one of several Pennsylvanian stratigraphic units in eastern Massachusetts. It is mainly conglomerate and greywacke, exclusive to the Bellingham Basin. The conglomerate has granite and quartzite pebbles in a mica matrix, sourced from the neighboring Blackstone Group and Milford Granite (which has locally unique blue quartz). The two main rock types are interbedded with chlorite phyllite which contains minerals such as muscovite, quartz, zoisite, magnetite and chloritoid. The formation may be the same age as the Roxbury Conglomerate in the .