Geologic units in Merrimack county, New Hampshire

Additional scientific data in this geographic area

Kinsman Granodiorite (Early Devonian) at surface, covers 25 % of this area

(Kinsman Quartz Monzonite of Billings, 1955) - Foliated granite, granodiorite, tonalite, and minor quartz diorite; large megacrysts of potassium feldspar characteristic; garnet locally abundant.

Lower part of Rangeley Formation (Lower Silurian (Llandoverian)) at surface, covers 19 % of this area

Gray, thinly laminated (5-25 mm) metapelite with local lentils of turbidites and thin quartz conglomerates in western New Hampshire. Sparse calc-silicate pods and coticule. Probably equivalent to member B of Rangeley Formation of Maine.

Concord Granite (Late Devonian) at surface, covers 19 % of this area

Gray two-mica granite, locally grading to tonalite.

Upper part of Rangeley Formation (Lower Silurian (Llandoverian)) at surface, covers 10 % of this area

Rusty-weathering, pelitic schist, metasandstone, and local coarse-grained metasandstone lentils; calc-silicate pods common; minor coticule. Probably equivalent to member C of Rangeley Formation of Maine.

Spaulding Tonalite (Early Devonian) at surface, covers 9 % of this area

(Spaulding Quartz Diorite of Fowler-Billings, 1949) - Weakly foliated to nonfoliated, spotted biotite quartz diorite, tonalite, granodiorite, and granite; garnet and muscovite may or may not be present.

Perry Mountain Formation, undivided (Lower? - Middle? Silurian) at surface, covers 5 % of this area

Sharply interbedded quartzites, light-gray nongraphitic metapelite, and "fast-graded" meta-turbidites. Coticule layers common.

Smalls Falls Formation, undivided (Upper to Middle Silurian (Ludlovian and Wenlockian)) at surface, covers 3 % of this area

Very rusty weathering, thinly bedded sulfidic-graphitic schist and pyrrhotitic calc-silicate granofels. Eastern facies equivalent to lower part of the Fitch Formation. Locally mapped as Francestown Formation of Nielson (1981) in southern New Hampshire.

Littleton Formation, Lower unnamed member (Lower Devonian) at surface, covers 2 % of this area

Thinly or poorly bedded aluminous lower part, somewhat rusty. Rare quartzite lentils. Carrabassett Formation in northwestern Maine is probably correlative.

Littleton Formation, undivided (Lower Devonian; Siegenian) at surface, covers 2 % of this area

Gray metapelite and metawacke and subordinate metavolcanic rocks; generally, but not everywhere, conformable with underlying Fitch or Madrid Formations. Fossiliferous in western New Hampshire.

Littleton Formation, Upper unnamed member (Lower Devonian) at surface, covers 2 % of this area

Light-gray metaturbidite, lithologically identical to, and probably correlative with, the Seboomook Formation of Maine. Coticule layers common.

Madrid Formation (Upper Silurian?) at surface, covers 2 % of this area

Massive to weakly foliated, purple biotite-feldspar granofels, layered calc-silicate, and dark pelitic-sulfidic schist containing calc-silicate pods in upper member; an eastern facies equivalent to the upper part of the Fitch Formation. Locally mapped as the Warner Formation of Nielson (1981) in southern New Hampshire.

Massabesic Gneiss Complex (Late Proterozoic) at surface, covers 0.6 % of this area

Quartzose-feldspathic gneiss and biotite schists (locally rusty), granofels, and cal-silicate rocks closely intruded by, and grading into, a pink gneissic granite (623 Ma) that produced a migmatite.

Merrimack Group, Berwick Formation (Ordovician? - Silurian?) at surface, covers 0.5 % of this area

Purple biotite-quartz-feldspar granofels or schist and interbeds of calc-silicate granofels and minor metapelites. Stratigraphic sequence with respect to Eliot Formation uncertain

Two-mica tonalite (Early - Late Devonian) at surface, covers 0.5 % of this area

Similar to Concord Granite; found in south-central New Hampshire.

Hypersthene-biotite quartz diorite and hornblende or actinolite diorite or gabbro (Early Devonian - Late Devonian) at surface, covers 0.3 % of this area

Spatially associated with Spaulding Tonalite plutons.

Bethlehem Granodiorite (Early Devonian) at surface, covers < 0.1 % of this area

(Bethlehem Gneiss of Billings, 1955) - Gray, strongly foliated biotite-muscovite granodiorite and associated tonalite and granite.

Biotite tonalite (Early - Late Devonian) at surface, covers < 0.1 % of this area

Dark-gray; found in southeastern and western New Hampshire.

Fitch Formation (Upper Silurian; Pridolian and Ludlovian) (Upper Silurian - (Pridolian and Ludlovian)) at surface, covers < 0.1 % of this area

Metamorphosed limestone, calcareous sandstone, siltstone, and dark pelitic schist; lower contact is disconformable on the Clough Quartzite. Fossiliferous.