Radiometric dating
Radiometric dating (Rb-Sr) indicates the Guilford Quartz Monzonite is 425 Ma (Silurian). However, A. A. Drake argued that the Guilford is of Ordovician age because it is probably comagmatic with the Woodstock Quartz Monzonite dated at 444 Ma. One other source gives the date of 420 +/-50 Ma.