NEW ENGLAND APPALACHIAN SYSTEMS 



175 



places at the base, black slate and fine-grained, light quartzite alternate 

 in beds a quarter of an inch thick. 



The Clough conglomerate is one of the best key horizons in western 

 New Hampshire, and although thin, it is resistant and exceptionally well 

 represented in outcrops. It apparently continues southward to the Massa- 

 chusetts boundary. Its outcrops are generally white cliffs. The pebbles in 

 the conglomerate are chiefly vein quartz, but some are quartzite, jasper, 

 greenstone, or soda-rhyolite. In places only a few pebbles are present; in 

 others they constitute over 60 percent of the rock (Billings, 1937). The 

 matrix is pure or slightly impure quartzite. 



The Clough conglomerate directly underlies the Fitch formation which 

 carries middle Silurian fossils. Moreover, the two formations are closely related 

 in age, for a few beds of quartz conglomerate are found in the Fitch. The 

 Clough conglomerate, however, is separated from the underlying strata by an 

 unconformity. It is apparent that the formation is either middle or lower 

 Silurian. In many respects the Clough is similar to the Shawangunk conglomer- 

 ate of New York, although the former is thinner and purer. The Clough under- 

 lies fossiliferous middle Silurian, and the Shawangunk carries middle Silurian 

 fossils in its upper part. The two are closely related, if not identical, in age 

 (Billings, 1937). 



The Fitch formation in its least altered form consists of white to buff 

 marble; gray limestone and marble; buff dolomitic slate; buff to brown 

 arenaceous dolomitic limestone; gray calcareous slate ("trilobite slate" of 

 earlier workers); white to gray arenaceous limestone and calcareous, 

 arkosic conglomerate; gray impure quartzite; white to gray arkose; white 

 quartz conglomerate; and gray slate. Fossils have been found at two 

 localities in the Fitch formation southeast of the Ammonoosuc thrust, and 

 are recognized as of Middle Silurian (Niagaran age). 



The Littleton formation of Lower Devonian age consists in its least 

 metamorphosed condition chiefly of slate and sandstone, with subordinate 

 amounts of soda-rhyolite conglomerate, tuff and breccia, and some green- 

 stone. 



Formations older than those listed in the chart of Fig. 11.21 are known. 

 The Orfordville formation, first recognized in west central New Hamp- 

 shire (Kruger, 1946) underlies the Albee formation, and the Waits River 

 formation first found in central Vermont, underlies the Orfordville ( Cur- 



rier and Jahns, 1941). The base of the Waits River is 2000 feet abo' 

 crinoidal limestone which appears to be Middle Ordovician. If so, both 

 the Waits River and Orfordville are Middle Ordovician or vounger. The 

 Orfordville formation was originally' a shale with very thin beds of sand- 

 stone, and the Waits River a calcareous shale and limestone formation. 



Structure 



General Statement. In Massachusetts and southern New Hampshire 

 the structures trend northerly; in northern New Hampshire they veer 

 northeasterly. A succession of anticlinoria and synclinoria make up the 

 major elements of the structure. See Figs. 11.20 and 11.26. Proceeding 

 eastward from the great monocline of central and eastern Vermont three 

 thrust faults occur, and between the middle ( Ammonoosuc ) and eastern 

 ( Northey Hill ) is the Connecticut Valley synclinorium. This lies approxi- 

 mately astride the boundary line of Vermont and New Hampshire. Next 

 east is the Bronson Hill anticline, the Merrimack synclinorium and in 

 southeastern New Hampshire the Rockingham anticlinorium. The Coos 

 anticlinorium is in the northern part of the state and lies between the 

 Monroe and Ammonoosuc thrusts. 



The older plutonic series, especially the Oliverian and New Hampshire 

 series, participate in the northerly and northeasternly trend. This may 

 be seen by the Oliverian series making up the cores of the domes along 

 the Bronson anticline, and by the foliated Mt. Clough and Cardigan 

 plutons of the New Hampshire series striking along the western flank of 

 the Merrimack synclinorium. 



Bronson Hill Anticline. The Bronson Hill anticline extends from 

 Massachusetts to Maine, a length of 150 miles. It ranges from 6 to 16 

 miles wide. The core is composed of the Ammonoosuc volcanics and the 

 Oliverian plutons with the Clough, Fitch, and Littleton formations on 

 both flanks. 



Rockingham Anticlinorium. The Rockingham anticlinorium. lies in 

 southeastern New Hampshire, between the Atlantic Ocean and the Fitch- 

 burg pluton. The individual folds of the anticlinorium are, from south- 

 east to northwest, the Rye anticline, the Great Bay (Eliot) syncline. and 

 the Exeter anticline (largely occupied by the Exeter pluton). 



