The Norfolk Basin is synclinal basin, partially bounded by faults, running east-northeast between the Dedham Block and the Foxborough Block. It contains the folded and cleaved, but unmetamorphosed Wamsutta Formation and Pondville Conglomerate, which both formed in the

Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the International Commission on Stratigraphy, ICS geologic timesca ...

, also known as the Late Carboniferous 323 to 298 million years ago. The basin is separated from the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

Dedham Granite of the southeastern Massachusetts

batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such ...

by the Ponkapoag Fault. Further east, the Ponkapoag Fault cuts out the

sedimentary rocks, so that the Ordovician-

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

Quincy Granite and the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

Braintree Formation directly contact the Dedham Granite. The Ponkapoag Fault, near Weymouth, also splits up the Wamsutta Formation between the Norfolk Basin and the nearby Narragansett Basin.

Northern Norfolk Basin

An unconformity separates the basin from the Blue Hills in the northeast where it tapers out. The Pondville Conglomerate, lying atop the Blue Hill Granite Porphyry dips 60 degrees south.

Southern Norfolk Basin

Felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...

volcanic rock flanks the basin in the southwest and it is fragmented by numerous small faults. The Sharon Syenite, exposed just south of Franklin on I-495 indicates this, with a high-degree of fracturing. In fact, an inlier of Dedham Granite splits the formation in two in the southwest.

References

{{reflist Geology of Massachusetts Natural history of Massachusetts