Given below are special, more-detailed explanations of several topics encountered in the self-guided tours of the Middlesex Fells Reservation.

Geologic Time Scale – To see an updated version of the geologic time scale showing time units and their numerical ages see: TIME SCALE

Plutons – For more on plutons and how they form: PLUTONS

Radiometric Ages – For more on how numerical ages of rock formations are determined using radiometric dating: RADIOMETRIC AGES

Unconformities – For more information on unconformities: UNCONFORMITIES

Light-colored Volcanic Rocks in the Middlesex Fells. This is a picture catalog of the types and textures of light-colored (felsic or sialic: rhyolitic and dacitic) volcanic rocks that occur in the Fells: VOLCANIC ROCKS