Guilford Quartz Monznoite

Biotite-muscovite-quartz monzonite; occurs as discontinuous lenticular bodies; age 420 +/- 50 m.y. * by radiogenic dating.
State Maryland
Name Guilford Quartz Monznoite
Geologic age Silurian
Lithologic constituents
Igneous > Plutonic > Syenitic > Quartz-monzonite
Comments Radiogenic date from Wetherill et al., 1966. (ref. MD003). Also second age date reference from USGS Geologic Names lexicon (ref. MD004): Isotopic dating (Rb-Sr) of the Guilford Quartz Monzonite indicates the unit is of Silurian age (425 Ma).

Cleaves, E.T., Edwards, J., Jr., and Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.

In 1995 the Water Resources Division of the U.S. Geological Survey digitized the geologic map of Maryland from the 1968 paper map (Reference MD001). Information about products from the Maryland Geological Survey can be found at

Wetherill, G.W., Tilton, G.R., Davis, G.L., Hart, S.R., and Hopson, C.A., 1966, Age measurements in the Maryland Piedmont: Journal of Geophysical Research, v. 71, p. 2139-2155.

USGS Geologic Names lexicon found at:

NGMDB product
Counties Howard