Hawley Formation (MAOhb;0)

Hawley Formation - Black, fine-grained, splintery, rusty-weathering schist and thin dark quartzite; interlayered amphibolite commonly has plagioclase megacrysts. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

State	Massachusetts
Name	Hawley Formation
Geologic age	Middle Ordovician
Original map label	Ohb
Comments	Part of Rowe-Hawley Zone (Ordovician and Older Rocks) Secondary unit description per MA013.
Primary rock type	schist
Secondary rock type	quartzite
Other rock types	amphibolite
Lithologic constituents	Major Metamorphic > Metasedimentary > Metaclastic > Quartzite Metamorphic > Schist Minor Metamorphic > Amphiboliteinterlayered amphibolite commonly has plagioclase megacrysts
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
Unit references	Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000. Trzcienski, W.E., Thompson, J.B., Jr., Rosenfeld, J.L. and Hepburn, J.C., 1992, The Chicken Yard line/Whately fault debate; from Springfield, Vermont, to Whately, Massachusetts, IN Robinson, Peter, and Brady, J.B., eds., Guidebook for field trips in the Connecticut Valley region of Massachusetts and adjacent states; Volume 2: University of Massachusetts, Geology Department Contribution, no. 66, New England Intercollegiate Geological Conference, 84th Annual Meeting, Amherst, MA, October, 9-11, 1992, p. 291-304.
Geographic coverage	Franklin - Hampden - Hampshire