A Field Trip Guidebook to the Type Localities of Marland 

Billings’ 1935 Paleozoic Bedrock Stratigraphy Near 

Littleton, New Hampshire

By Douglas W. Rankin and Mary B. Rankin

Open-File Report 2014–1026

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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The field trip described in this report was led on March 17, 2013.

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endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also may

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must be secured from the copyright owner.

Suggested citation:

Rankin, D.W., and Rankin, M.B., 2014, A field trip guidebook to the type localities of Marland Billings’ 1935 

Paleozoic bedrock stratigraphy near Littleton, New Hampshire: U.S. Geological Survey Open-File Report 

2014‒1026, 21 p., http://dx.doi.org/10.3133/ofr20141026.

ISSN 2331-1258 (online)
iii

Contents

Introduction.................................................................................................................................................................... 1

Geologic Setting ............................................................................................................................................................ 8

Road Log ....................................................................................................................................................................... 9

Stop 1. Albee Formation (OЄal)............................................................................................................................... 11

Stop 2. Sulfidic black slate, Partridge Formation (Op).............................................................................................. 12

Stop 3. Rhyolite tuff-breccia, Ammonoosuc Volcanics (Oar).................................................................................... 12

Stop 4. Rhyolite, Ammonoosuc Volcanics (Oar) ...................................................................................................... 13

Stop 5. Fitch Formation............................................................................................................................................ 14

Stop 6. Pelitic facies of the Littleton Formation (Dl).................................................................................................. 14

Stop 7. Sandy facies of the Littleton Formation (Dl)................................................................................................. 15

Stop 8. Rhyolite/mudstone debris flow interlayered with rhyolite aphanitic tuff and black slate (Oar) ...................... 16

Stop 9. Sulfidic black slate, Ammonoosuc Volcanics (Oap)..................................................................................... 17

Stop 10. Clough Quartzite and Fitch Formation ....................................................................................................... 17

Stop 11 (optional). Ammonoosuc Volcanics............................................................................................................. 18

References Cited......................................................................................................................................................... 19

Figures

1. Geologic map of the Littleton 15-minute quadrangle, New Hampshire ..............................................................5

2. Geologic map of the Littleton area, New Hampshire..........................................................................................7

3. Topographic map of the Littleton area, New Hampshire..................................................................................10

Table

1. Description of map units in the Littleton-Moosilauke area, New Hampshire. .....................................................2
iv

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

square mile (mi2) 2.590 square kilometer (km2) 

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd)

Area

square kilometer (km2) 0.3861 square mile (mi2)
1

A Field Trip Guidebook to the Type Localities of Marland

Billings’ 1935 Paleozoic Bedrock Stratigraphy Near 

Littleton, New Hampshire

By Douglas W. Rankin and Mary B. Rankin

Introduction

During the course of his Ph.D. research at Harvard University on the geology of the North 

Conway quadrangle, Billings (1928) puzzled over the age of the metasedimentary gneisses and schists 

(his Montalban schists) that were host to the plutonic rocks. When he returned to Harvard as an assistant 

professor in 1931, after a stint of teaching at Bryn Mawr College, he looked for a place in which field 

mapping might shed light on the problem. He chose the Littleton area, then the only terrain in New 

Hampshire known to contain Paleozoic fossils. Coinciding with the early stages of this work, he 

provided George W. Stose of the U.S. Geological Survey an interpretive map of the geology of central 

New Hampshire (Billings, 1934). Based largely on this map, central New Hampshire is shown on the 

1932 geologic map of the United States as “pre-Cambrian, some early Paleozoic rocks may be included”

(Stose and Ljungstedt, 1932). Thus it was Billings who made that call and Billings who almost 

immediately changed it. 

With the assistance of two or three graduate students each year, Billings completed the geologic 

mapping of the New Hampshire part of the Littleton 15-minute quadrangle as well as the entire 

Moosilauke 15-minute quadrangle (which adjoins Littleton to the south) in a little over three summers. 

The New Hampshire State Planning and Development Commission published the maps along with the 

definitions of stratigraphic units in 1935 (Billings, 1935). The maps and a much expanded text appeared 

in the Geological Society of America Bulletin (Billings, 1937) in what has become a classic paper 

demonstrating that the simultaneous application of the principles of stratigraphy, structural geology, and 

igneous and metamorphic petrology to the mapping of outcrops could lead to breakthroughs in regional 

interpretations. In the words of Walter White (1968), this work provided the stratigraphic key to the 

geology of western New Hampshire, and laid the foundation upon which a major part of subsequent 

work in New England has been directly or indirectly built.

Billings established and named a succession of six stratigraphic units in the rocks of low 

metamorphic grade west of Littleton (the Littleton Formation, Fitch Formation, Clough Quartzite, 

Partridge Formation, Ammonoosuc Volcanics, and Albee Formation; see table 1). The two youngest 

units, the calcareous Fitch Formation and the turbiditic Littleton Formation, are fossiliferous in the area, 

with ages established by Billings and Cleaves (1934) as “middle” Silurian and Early Devonian, 

respectively. The Clough Quartzite, which underlies the Fitch, provided structural control. According to 

Billings (1935, p. 13), “The Clough Conglomerate (now Quartzite) is undoubtedly the best key horizon

in western New Hampshire. It is very distinctive, readily recognized, thin but resistant, and most 

invariably outcrops wherever it exists. A study of the geologic structure of the area resolves itself in 

part into a careful mapping of the Clough.” Billings and students recognized and mapped the same 
2

stratigraphic section, or parts thereof, with units in the same stratigraphic order where not disturbed by 

faulting, in adjacent areas of progressively higher regional metamorphic grade to the east and south.

The Littleton Formation in parts of the Moosilauke quadrangle contains the assemblage muscovitesillimanite. Finally, Billings and Cleaves (1934) described a brachiopod identified as Spirifer sp. ind. 

from the sillimanite-bearing rocks near Mount Moosilauke. 

Table 1. Description of map units in the Littleton-Moosilauke area, New Hampshire.

[Map units are shown in figure 2. Abbreviations: mm, millimeter; cm, centimeter; km, kilometer]

Formation Map unit Description Age

Eastern Vermont Sequence

Stratified rocks

Gile Mountain 

Formation

Dg Interlayered light-gray to tan micaceous metasandstone and 

medium- to dark-gray to grayish-black, graphitic and commonly 

sulfidic slate. Minor calcareous metasandstone and calcareous 

ironstone. Graded bedding common.

Lower Devonian

Meetinghouse 

Slate Member

Dgm Medium-dark-gray to grayish-black slate containing sparse to 

moderately abundant 1-mm- to 1-cm-thick beds of light-gray, 

fine-grained metasandstone and metasiltstone, commonly sulfidic 

and calcareous. Some graded bedding. Gradational contact with 

Dg.

Boundary Mountains-Bronson Hill Sequence

Stratified rocks

Littleton 

Formation

Dl Medium-dark-gray to dark-gray slate and schist interlayered with 

light-gray, fine-grained micaceous metasandstone. Sparse grit. 

Locally highly pyritic and rusty weathering, with pyrite crystals 

as large as 2 cm. Contains mappable units of mafic and felsic 

volcanic and volcaniclastic rocks; includes Dlr, which consists of 

metamorphosed aphanitic to very fine grained tuff, welded tuff, 

lithic tuff (commonly with a few percent quartz and alkali 

feldspar phenocrysts), and volcanic conglomerate. (Dlr is not 

shown in figure 2.)

Lower Devonian 

(Emsian: Walker 

Mtn.; Pragian: Mt. 

Moosilauke)

Fitch Formation

and Clough 

Quartzite

Sfc Fitch Formation and Clough Quartzite, undivided. 

Fitch Formation: Metamorphosed limestone, calcareous 

sandstone, siltstone, and pelite. Some limestone conglomerate 

and polymict conglomerate with calcareous matrix.

Upper Silurian

(Pridolian)

Clough Quartzite: Metamorphosed quartz-cobble to -pebble 

conglomerate, quartzite, and micaceous sandstone.

Lower Silurian

(Llandoverian)

Partridge 

Formation 

Op Dark-gray to grayish-black, rusty-weathering, sulfidic slate 

interlayered locally with metamorphosed rhyolite (Opr). Where 

the sulfide is pyrrhotite as opposed to pyrite, rusty weathering is 

pronounced (“cruddy black slate”). 

Upper Ordovician

Ammonoosuc 

Volcanics

Metamorphosed felsic and mafic volcanic and volcaniclastic 

rocks, pelite, and ironstone.

Middle and Upper 

Ordovician
3

Table 1. Description of map units in the Littleton-Moosilauke area, New Hampshire.—Continued

[Map units are shown in figure 2. Abbreviations: mm, millimeter; cm, centimeter; km, kilometer]

Formation Map unit Description Age

Boundary Mountains-Bronson Hill Sequence—Continued

Oar Dominantly metamorphosed rhyolite tuff, lapilli tuff, tuffbreccia, and lava. Generally porphyritic with 5 to 20 percent 

plagioclase and, in some, quartz phenocrysts. Generally strongly 

foliated with waxy sheen on foliation surfaces. Includes 

mappable units (not shown) of coarsely porphyritic rhyolite tuff, 

lapilli tuff, and tuff-breccia, in which quartz and plagioclase 

phenocrysts are commonly as large as 5 mm.

Oaa Dominantly metamorphosed andesitic and basaltic tuff, crystal 

tuff, and tuff-breccia; minor pillow lava. Commonly contains

relict plagioclase and (or) mafic phenocrysts.

Oat Metamorphosed medium- to light-bluish-gray aphyric rhyolite 

tuff and siltstone.

Oad

(=Sfc)

Metamorphosed light-bluish-gray, rusty-weathering, siliceous 

and argillaceous dolomite and calcareous siltstone.

Now reinterpreted as Fitch Formation. Reassigned to the Fitch 

Formation.

Oam Metamorphosed medium-light-bluish-gray, medium-bluish-gray, 

medium-dark-gray, to medium-dark-greenish-gray siltstone and 

phyllite, medium-gray feldspathic wacke, and grit. Purple tinge 

common; coticules and magnetite locally abundant.

Oap Dark-gray to grayish-black, rusty-weathering sulfidic slate and 

phyllite interlayered with metamorphosed ultra-fine-grained, 

sulfidic ironstone, chert, felsic tuff, and minor sandstone. Much is 

indistinguishable from the Partridge Formation.

Albee Formation OЄal Interbedded light-gray to greenish-gray, white-weathering, 

feldspathic, fine-grained metamorphosed sandstone and siltstone, 

and light-gray to greenish-gray to dark-gray phyllite. Lesser 

amounts of quartzite. Rare calc-silicate nodules. Phyllosilicates 

commonly 10 to 25 percent of matrix. Tourmaline and magnetite 

are sporadic accessory minerals. May be sulfidic (either pyrite or

pyrrhotite) and rusty weathering. Generally sharply bedded but 

graded beds as well as slump structures are locally obvious. 

Bedding thickness varies between less than a centimeter to more 

than a meter. Pinstriping is common (quartzofeldspathic laminae 

1 mm to a few millimeters thick separated by paper-thin 

micaceous partings, commonly magnetite-bearing). 

Upper Cambrian to 

Middle Ordovician

Scarritt Member OЄals Dark-gray slate interlayered with thin beds of light-gray, finegrained, micaceous and feldspathic metamorphosed sandstone. 

Ribby-weathering common but in places where pelite dominates, 

bedding is difficult to identify. Abruptly graded beds less than 1

cm to 30 cm thick are locally common, as is channeling and, in 

places, soft-sediment deformation. Commonly sulfidic (either 

pyrite or pyrrhotite) and rusty weathering.
4

Table 1. Description of map units in the Littleton-Moosilauke area, New Hampshire.—Continued

[Map units are shown in figure 2. Abbreviations: mm, millimeter; cm, centimeter; km, kilometer]

Formation Map unit Description Age

Boundary Mountains-Bronson Hill Sequence—Continued

Intrusive rocks

Piscataquis 

magmatic

belt

Dgp

Dm

Granite and quartz monzonite, commonly intrusive into Emsian 

strata.

Diorite and gabbro, commonly intrusive into Emsian strata.

Early Devonian

(Emsian)

Comerford 

Intrusive 

Complex 

Mafic to intermediate intrusive complex. Latest Silurian

Scm Foliated to nonfoliated, fine-grained to pegmatitic 

metamorphosed gabbro, diorite, and tonalite; aplitic tonalite; and 

crosscutting diabase dikes. Twenty fractions of zircon and 

baddeleyite from three sample sites of pegmatitic phases have a 

weighted mean 207Pb/206Pb age of 419±1 Ma (Rankin and others, 

2007).

Scd Foliated to weakly foliated, metamorphosed tholeiitic gabbro to 

diorite dikes. Where the dikes are abundant, sheeted dikes are 

common. Chilled margins common. Extensive alteration with as 

much as 20 percent calcite in some locations. Shown by overprint 

where dikes make up roughly 50 percent of the area.

Highlandcroft 

Granodiorite

Ohi Foliated, medium-grained, metamorphosed granite, granodiorite, 

and tonalite containing quartz, microcline, saussuritized 

plagioclase, hornblende, biotite (chlorite alteration) and 

secondary calcite and sericite. U-Pb zircon age of 450±5 Ma 

(Lyons, Aleinikoff, and Zartman, 1986).

Late Ordovician

Oliverian 

Plutonic Suite

Oo Weakly to moderately foliated, medium-grained, commonly 

porphyritic, biotite granodiorite. U-Pb zircon ages range from 

456±3 to 447±4 Ma (Moench and Aleinikoff, 2003). Biotite 

trondhjemite from the Jefferson batholith about 8 km northwest 

of Berlin, N.H., has a U-Pb zircon age of 454±4 Ma.

Late Ordovician

Joslin Turn 

Tonalite

Oj Hypabyssal, medium-grained, weakly foliated, metamorphosed 

biotite tonalite. Granophyric intergrowths of quartz and 

plagioclase. U-Pb zircon age of 469±2 Ma (Moench and 

Aleinikoff, 2003).

Middle Ordovician

The type localities or areas of Billings’ classic six-fold Paleozoic stratigraphic section are all 

within 8 miles (mi) west or southwest of Exit 42 on Interstate Route 93 (I–93) at Littleton, N.H. (fig 1). 

All except the Clough Quartzite are in the Littleton 15-minute quadrangle. This field trip will visit

roadcuts as close as possible in March to these localities. Eleven stops are planned. All exposures are at 

chlorite grade of Acadian (?) metamorphism and all are within the Concord, Lisbon, Littleton, and 

Lower Waterford 7.5-minute quadrangles. As is true for most geological fieldwork, one can learn much 
5

by looking carefully at the outcrop without mutilating the ledge with a hammer. We ask you to use no 

hammers on the ledges at Stops 5, 7, and 8. Should you be lucky enough to see any fossils, please do not 

remove them from Stops 5 or 7.

Figure 1. Geologic map of the Littleton 15-minute quadrangle, New Hampshire (Billings, 1935), locating 

geographic features discussed in the text.

Although the focus of this field trip is on the work Marland Billings did 80 years ago, it is 

legitimate to ask to what extent have his interpretations of the Littleton-Moosilauke area been 

subsequently modified. With the exception of the major challenge of the Piermont-Frontenac allochthon

(Rankin, Tucker, and Amelin, 2013), Billings’ broad conclusions remain alive and well. We have 

subdivided some of his stratigraphic units. We now interpret the Ammonoosuc fault to be a Mesozoic 

normal fault rather than a Paleozoic thrust (Thompson and Norton, 1968). The paleontologic ages of the 

Fitch and Littleton Formations have been refined but remain Silurian and Devonian (Harris, Hatch, and 

Dutro, 1983; Boucot and Arndt, 1960), including one new locality on Mount Moosilauke in the Littleton 

Formation at sillimanite grade (Boucot and Rumble, 1980). The ages of several plutons and stratigraphic 

units are constrained by isotopic dating (Lyons, Aleinikoff, and Zartman, 1986; Moench and Aleinikoff, 
6

2003; Rankin and others, 2007; Rankin, Tucker, and Amelin, 2013). An episode of Silurian extension 

has been documented (Rankin and others, 2007), based in part on a suite of mafic dikes mapped by 

Billings (1937) prior to the concept of sheeted dikes. Geochemical data better characterizes several units 

(Moss, Haskin, and Dymek, 1996; Leo, 1985, 1991; Dorais, Workman, and Aggarwal, 2008; Rankin 

and others, 2007; Dorais and others, 2012).

Our work in the Littleton-Moosilauke area began in 1992 as part of the team making a new 

bedrock geologic map of Vermont (Ratcliffe and others, 2011) and is ongoing. The geologic map 

(fig. 2) is taken from Ratcliffe and others (2011) and, for the geology southeast of the Ammonoosuc 

fault, from Rankin, Tucker, and Amelin (2013). For the field trip, a preliminary version of the geologic 

map of the Littleton and Lower Waterford 7.5-minute quadrangles (the southern half of the Littleton 15-

minute quadrangle) is one of the props (D.W. Rankin, unpub. data, 2013). This preliminary map differs 

in detail from that of Billings (1935). Remember, however, that we were mapping at a larger scale than 

was he, we spent more time in the field than did he (albeit split over about twenty 7.5-minute 

quadrangles), and finally, we had his maps in hand.
7

Figure 2. Geologic map of the Littleton area, New Hampshire. Map units are described in table 1. The area 

northwest of the Ammonoosuc fault is modified from Ratcliffe and others (2011), and the area southeast of the 

Ammonoosuc fault is taken from Rankin, Tucker, and Amelin (2013). The map area is within the Concord, Miles 

Pond, Lower Waterford, Littleton, Lisbon, and Sugar Hill 7.5-minute quadrangles (see figure 3). X indicates the 

location of field trip stops; L is the location of the lunch stop.
8

The controversy of the Piermont-Frontenac allochthon is not the focus of this trip, but neither 

can it be avoided. Beginning in the 1980s, Moench and coworkers challenged the interpretation of a 

coherent stratigraphy in the Littleton-Moosilauke area as well as in much of the upper Connecticut 

Valley and initiated a controversy that has persisted for more than two decades (Moench, 1990, 1992; 

Moench and Aleinikoff, 2003; and Moench and others, 1987, 1995). They proposed that much of the 

section mapped as pre-Middle Ordovician Albee Formation of Billings (1937) was, instead, a thick, 

largely turbiditic Silurian sequence similar to what Moench (1971) had defined in the Rangeley area, 

Maine. The Silurian Rangeley sequence mapped by Moench and coworkers in the upper Connecticut 

Valley was hypothesized to constitute a 200-kilometer (km)-long Piermont-Frontenac allochthon 

transported westward in the latest Silurian to Early Devonian as a soft-sediment gravity slide on a 

hypothesized Foster Hill sole-fault.

We will not visit outcrops that shed light on this argument during this field trip, but we are sure 

the discussion will arise. Our mapping plus new uranium-lead (U-Pb) zircon ages by Tucker and Amelin 

cannot be reconciled with the existence of a large gravity-slide allochthon, although we confirm a much 

smaller (~25-km2) allochthon of Rangeley-like Silurian (?) turbidites near Piermont, N.H., about 45 km 

south-southwest of Littleton, which was emplaced by post-nappe-stage hard-rock thrusting. These

arguments are laid out in Rankin, Tucker, and Amelin (2013), which you may want to look at before the 

field trip.

Geologic Setting

The geologic setting is summarized from Rankin, Tucker, and Amelin (2013), wherein are 

extensive references to the supporting literature. Most of the Littleton-Moosilauke area is within the 

composite Boundary Mountains-Bronson Hill anticlinorium, a post-Early Devonian structure, which 

consists of Cambrian to Lower Devonian strata. It is the locus of the Middle Ordovician to earliest 

Silurian Bronson Hill magmatic arc (Ammonoosuc Volcanics, Partridge Formation, and Oliverian 

Plutonic Suite) that extends from Maine down the eastern side of the Connecticut River to Long Island 

Sound (for example, Hibbard and others, 2006). The deformed and partly eroded arc is locally overlain 

by a relatively thin Silurian section (Clough Quartzite and Fitch Formation) that thickens markedly 

eastward across a syn-sedimentary tectonic hinge line (east of the Littleton area) to as much as 5 km in 

the Central Maine trough (Rangeley sequence). The Silurian section near Littleton is disconformably 

overlain by a thicker Lower Devonian section that includes volcanic rocks (Littleton Formation). 

The pre-Middle Ordovician rocks were probably deformed by the pre-Middle Ordovician 

Penobscottian orogeny and all the pre-Silurian rocks by the Late Ordovician Taconian orogeny. In the 

Littleton-Moosilauke area Billings (1935, 1937) recognized a series Acadian folds. From northwest to 

southeast, they are the Gardner Mountain anticline (more of an arch, with Albee Formation flanked by 

Ammonoosuc Volcanics; Billings also refers to it as an arch), Walker Mountain syncline, Salmon Hole 

Brook syncline, Garnet Hill syncline, and Bronson Hill anticline. Billings (1956) suggested that the 

Gardner Mountain anticline is the southwestern extension of a broader regional structure, the Coos 

anticlinorium, which was better defined and renamed the Boundary Mountain (sic) anticlinorium by 

Albee (1961). Billings also recognized the increasing structural complexity to the southeast and 

renamed the Bronson Hill an anticlinorium. 

South of Littleton, the Bronson Hill anticlinorium (southeast of the Ammonoosuc River in 

figure 2) is characterized by mantled gneiss domes consisting of 456- to 442-Ma core gneisses of 

probable intrusive igneous origin, overlain by a cover sequence consisting of Ammonoosuc Volcanics to 

Littleton Formation. The core gneisses are grouped into the Oliverian Plutonic Suite. The formation of 

the gneiss domes, perhaps due to the gravitational rise of the Oliverian cores, was preceded by the 
9

formation of Alpine-scale west-directed fold and thrust nappes involving Emsian and older strata. The 

timing of pulses of deformation and metamorphism to the south is complex and extends into the late 

Paleozoic.

A number of Mesozoic normal faults, the most prominent of which is the west-dipping 

Ammonoosuc fault, also cuts the Boundary Mountains-Bronson Hill anticlinorium. Near Piermont, 

N.H., it juxtaposes kyanite-grade rocks on the east against chlorite-grade rocks on the west. The amount 

of displacement decreases to the northeast into north-central New Hampshire.

The composite Boundary Mountains-Bronson Hill sequence is separated from the Silurian and 

Devonian rocks of the Eastern Vermont sequence to the west by the Monroe fault, interpreted to be a 

west-directed, steeply dipping late Acadian thrust fault. 

Road Log

Cumulative Mileage and Stop Descriptions

0.0 Front door, Mount Washington House.

0.6 Turn right onto U.S. Route 302 westbound.

14.3 Bethlehem town center. An ancient sign in the middle of town states that Bethlehem is the highest 

town east of the Rocky Mountains. Bethlehem’s elevation is about 1,475 feet (ft), which may make it 

the highest town in New England, but the statement overlooks many towns at higher elevations 

farther south in the Appalachians and in the Great Plains.

17.5 Bear right onto I–93 northbound at Exit 40.

19.0 Pass Exit 41, East Littleton.

Littleton 7.5-minute quadrangle. The field trip stops are indicated in figures 2 and 3.
10

Figure 3. Topographic map of the Littleton area, New Hampshire. Names and boundaries of 7.5-minute 

quadrangles are shown. Field trip stops are numbered and indicated by X; lunch stop location is indicated 

by L.

21.0–21.2 Amphibolite, Ammonoosuc Volcanics (unit Oaa).

22.7 Pass Exit 42, West Littleton and U.S. 302.

23.4 The nonconformity between the Highlandcroft Granodiorite (Oh) and the Fitch Formation (Sf) is 

exposed at the south end of the roadcut (left). 

23.9 Pass Exit 43; Highlandcroft Granodiorite roadcuts on both sides of exit. This location is Stop A2 of 

New England Intercollegiate Geological Conference (NEIGC) 1996 field trip (Rankin, 1996).

25.1 Roadcut on right; Highlandcroft Granodiorite.
11

26.1–26.4 Long roadcut, Ammonoosuc Volcanics. Rhyolite at east end followed by a thick section of 

hornblende andesite. A Mesozoic mafic dike is exposed on both sides of the road.

27.4 Moore Reservoir causeway. On far (west) side of causeway, a long series of ledges some distance 

to the left of the Interstate consist of rhyolite of the Ammonoosuc Volcanics (Oar).

27.7 White-weathering silicified rhyolite (Oar).

27.9 Partridge Formation (Op).

28.3 Bear right on Exit 44 through roadcuts of Oar.

28.6 Turn left onto N.H. Route 18/135 and pass Moore Dam, now owned by TransCanada. The dam 

opened in 1957, has a height of 178 ft, and backs up a reservoir of 3,490 acres.

Cross the unexposed hypabyssal Joslin Turn Tonalite. It is exposed in a small outcrop along I–93, 

and Billings (1935) mapped a small body of plutonic rock here that he called Highlandcroft 

Granodiorite. Moench and Aleinikoff (2003) reported a U-Pb zircon age of 469±2 Ma for the Joslin 

Turn from the more extensive part of the pluton in adjacent Vermont (Eric and Dennis, 1958). 

Moench and Aleinikoff (2003) interpreted the Joslin Turn to be intrusive into the Ammonoosuc

Volcanics, as do we. This surprisingly old age for the Joslin Turn greatly complicates the internal 

stratigraphy and provenance of the Ammonoosuc. Moench and Aleinikoff (2003) also reported a 

U-Pb zircon age of 443±4 Ma for rhyolite tuff breccia of the Ammonoosuc from Bath, N.H., east of 

the Ammonoosuc fault along the Ammonoosuc River. We will return to this topic later. 

Lower Waterford 7.5-minute quadrangle.

29.4 Bear right on N.H. 18.

29.6 Cross Connecticut River into Vermont on Vt. Route 18.

30.7 Village of Lower Waterford and home of upscale Rabbit Hill Inn.

Concord 7.5-minute quadrangle.

32.7 Roadcut on left is Stop 1. Tight parking on right or at turnaround ahead.

Stop 1. Albee Formation (OЄal)

Billings (1935) proposed the name Albee for slates and quartzites exposed on Gardner 

Mountain, which is in New Hampshire southwest of us. He designated the type locality as that part of 

Gardner Mountain between Hunt Mountain (Barnet quadrangle) and Albee Hill (Lower Waterford 

quadrangle) (fig. 1). Unfortunately, in March, there is no easy road access to outcrops of the Albee 

Formation in the type area.

The Albee Formation here is interlayered light-gray, fine-grained feldspathic, noncalcareous 

sandstone and greenish-gray to dark-gray pelite, some sulfidic. Much of the sandstone is pinstriped. In 

places one can see layering transposed into a steeply southeast-dipping foliation. 
12

33.1 Turn around at crest of hill, Remick Road.

Lower Waterford 7.5-minute quadrangle.

36.7 Junction with N.H. 135 just after crossing Connecticut River back into New Hampshire. Turn left 

onto N.H. 18/135.

Littleton 7.5-minute quadrangle.

37.5 Pass entrance (northbound) to I–93 (Exit 44) and continue on N.H. 18/135.

Roadcut east of the I–93 entrance is brecciated Highlandcroft Granodiorite interpreted to be in the 

hanging wall of an east-dipping Mesozoic (?) Moore Reservoir fault (fig. 2). As an alternative 

viewpoint, Moench (1999, Stop 5) described this as interfingering of Joslin Turn Tonalite and 

Ammonoosuc Volcanics. Thin sections show no granophyric texture (a trademark of Joslin Turn) 

and no interfingering rhyolite, but much shearing and brecciation.

Pass under I–93 and pass entrance, left, to rest area (closed for the season).

38.5 Roadcut on right is Stop 2.

Stop 2. Sulfidic black slate, Partridge Formation (Op)

Billings (1935) designated nearby Partridge Lake, about one mile on strike to the southsouthwest, as the type locality. There are no outcrops of the Partridge on Partridge Lake that are easily 

accessible to us today. This is typical graphitic, rusty weathering “cruddy black slate” (CBS) of the 

Partridge. As Billings noted, cleavage is conspicuous, but bedding is rarely observed. A revisit to this 

outcrop in August 2013 showed that bedding is faintly visible (N. 10o E.–70o E.) The dominant cleavage 

bears N. 10o E.–70o W. The intersection of this with a second cleavage (N. 40o E.–75o W.) produces a 

penciling that bears N. 95o W. and plunges 70o W. The sulfide is too fine grained to resolve, but at this 

low metamorphic grade, it is probably pyrite.

Billings mapped the Partridge as overlying the Ammonoosuc Volcanics and underlying the 

Clough Quartzite. That is clearly true for much of the Partridge. We are convinced, however, that 

deposition of black slate also overlapped in time with the Ammonoosuc Volcanics. We will discuss this 

further at Stops 8 and 9. 

Continue south on N.H. 18/135 to mile 38.7. This is Stop 3.

Stop 3. Rhyolite tuff-breccia, Ammonoosuc Volcanics (Oar)

Billings (1935) proposed the name Ammonoosuc Volcanics for volcanic rocks that overlie the 

Albee Formation and underlie the Partridge Formation. He designated the type area as the region 

bounded by Slate Ledge School (intersection of Gannon and Slate Ledge Roads, Littleton quadrangle), 

Partridge Lake, Ogontz Lake, and Tinkerville (all in the Lower Waterford quadrangle) (fig. 1). Billings 

took the name from the Ammonoosuc River, which flows south from Littleton a few miles to the 

southeast. He notes that the Ammonoosuc Volcanics is well exposed along the river, but is of higher 
13

metamorphic grade. The rhyolite here at Stop 3 is about half a mile north of the type area and is 

interpreted to be continuous in the subsurface with the type area.

The Ammonoosuc is a complex unit of interlayered and interfingering volcanic and

volcaniclastic rocks, pelite, siltstone, and ironstone (table 1); compositions range from basalt to rhyolite. 

We have attempted to map rock types within the Ammonoosuc. These are generalized subdivisions 

representing a dominant rock type but commonly containing interlayers of the other lithologies. 

Unfortunately there are no viable roadside outcrops of unit Oaa (mafic to intermediate volcanic rocks) 

of low metamorphic grade along our field trip route. Unit Oaa is spectacularly exposed along I–93 on 

the long hill up from the east side of Moore Reservoir (mile 26 in this road log). A stop there is not 

possible.

The rocks in the roadcut at Stop 3 are strongly foliated (N. 25o E.–75o W). Note the waxy luster 

on the foliation surfaces. One’s first impression of the rock is that it is a foliated but homogeneous 

aphanitic rhyolite containing scattered feldspar crystals, some as large as 1 centimeter (cm) across. In a 

few places in the roadcut one can see that much of the rock is fragmental, that is, a tuff breccia. This can 

be much better seen if one walks up to the relatively smooth top surface of the ledge. Most of the lithic 

clasts are quartz- and feldspar-phyric rhyolite. What is the age of this part of the Ammonoosuc? 

Because it is interpreted to underlie the immediately adjacent outcrop of Partridge (Stop 2), it could well 

belong to the younger, ~450-Ma, Ammonoosuc. On the other hand, this belt of unit Oar traces north 

across Moore Reservoir where it overlies the Ordovician-Cambrian Albee Formation near the Joslin 

Turn Tonalite (fig. 1 and farther northeast). It could be older than 469 Ma. We need more isotopic ages.

Continue across causeway over Moore Reservoir on N.H. 18/135 to mile 39.1, which is Stop 4.

Stop 4. Rhyolite, Ammonoosuc Volcanics (Oar)

The roadcut, left, is homogeneous-appearing, aphanitic, “porphyritic”, light-bluish-gray rhyolite. 

Again, this roadcut is about half a mile north of and on strike with rhyolite outcrops in the type area. 

Again, note the waxy luster on the foliation surfaces. The rhyolite contains about 10 percent phenocrysts 

of plagioclase and quartz in a ratio of about 4:1. The plagioclase is as large as 2 millimeters (mm), 

twinned, non-zoned, and some is glomerophyric; other crystals are broken. The quartz is rarely as large 

as 1 mm and some crystals are embayed. On the basis of one thin section the crystals have a large range 

in size and are unevenly distributed. The rhyolite is probably a crystal-lithic tuff, although rock 

fragments are not obvious in this non-weathered outcrop. Secondary minerals in the matrix/groundmass 

include sericite, epidote, and calcite; opaque minerals are rare. An analysis of the rhyolite normalized, 

volatile-free and with iron reduced shows 74.48 weight percent SiO2. A sample collected for U-Pb 

analysis was barren of zircons, although the rhyolite contains 153 ppm Zr.

Continue east on N.H. 18/135.

41.2 Entrance to Littleton Regional Hospital, our lunch site, and roadcut of Highlandcroft Granodiorite.

42.0 Site of the former G.E. Fitch Farm, left, from which the name Fitch Formation is taken. Parts of the 

collapsed barn remain. Billings (1935) designated the farm as the type locality of the Fitch, which 

crops out on the ridge to the right about 200 ft vertically above the road. Silurian fossils have been 

known from that locality for 131 years (Hitchcock, 1874) and most recently were examined by 
14

Harris, Hatch, and Dutro (1983). Conodonts date the Fitch here as no older than latest Ludlovian 

and at least as young as early Pridolian.

42.3 T-intersection. Turn right on the continuation of N.H. 18. Type locality of Highlandcroft Granodiorite 

is the knob on the far side of the intersection. Until about two years ago a barn stood on the knob 

with “Highland Croft” painted on its front in large white letters.

42.7 Roadcut on right. Park on left. This is Stop 5. WATCH OUT FOR TRAFFIC.

Stop 5. Fitch Formation

NO HAMMERS PLEASE AT THIS ROADCUT. Also, please do not remove fossils.

Billings (1935) proposed the name Fitch Formation for limestones and related sedimentary rocks 

of “middle” Silurian age in the Littleton area. Fitch ledges extend about 70 meters (m) along the road. 

The southeast part of the section consists of purplish-weathering, dark-gray calcareous metasiltstone and 

phyllite. The siltstone contains calcite segregations and veins. Pyrite cubes weather out to leave 

2- to 5-mm holes. Foliation is parallel to bedding (N. 45o E.–85o E.) and both are folded about an axis 

that plunges 25o to the southwest. In the middle of the section along the road is a disturbed zone and 

moderately east-dipping fault, thought to be an antithetic offshoot of the Ammonoosuc fault, which is

only about 600 m to the southeast. The slip surface is N. 50o E.–65o E. In this roadcut, the footwall of 

the fault includes, east to west, brecciated Highlandcroft Granodiorite followed by 2 m of bedded 

(N. 20o E.–75o W.) limestone conglomerate (silty matrix) containing Highlandcroft clasts. Possibly the 

brecciated Highlandcroft-conglomeratic Fitch contact represents the Highlandcroft-Fitch nonconformity 

that is also exposed along I–93 about 500 m to the north. The limestone conglomerate is succeeded to 

the northwest by 35 m of calcareous siltstone and the covered contact with the main Highlandcroft 

pluton. 

43.0 Dell Road; turn around.

45.8 Littleton Regional Hospital. LUNCH.

Exit hospital and turn left onto N.H. 18/135.

45.9 Turn right on Slate Ledge Road. Cross the unexposed belt of the Fitch Formation.

46.8 Park on “grass” near driveway on left and walk a short distance along the road to Slate Ledge 

Quarry (abandoned). We have the landowner’s permission to enter the quarry at our own risk. 

Enroute to the quarry we will pass scrappy ledges obscured by vegetation. We made a feeble 

attempt to clear these in September 2012. In 1997 toward the eastern end of the exposures, we 

observed graded beds (N. 50° E.–50° S.), topping east cut by cleavage (N. 70° E.–75° S.). Toward 

the western end of the exposures are tight, low-amplitude z-folds with axes N. 25° E. plunging 

65° W. Cleavage (N. 70° E.–75° S.) in fold noses is axial planar to the folds.

Stop 6. Pelitic facies of the Littleton Formation (Dl)

Billings (1935) modified the name Littleton argillite of Ross (1923) to Littleton Formation for 

slates, sandstones, and volcanic rocks in Littleton Township. He designated the type locality as around 
15

Slate Ledge, Walker Mountain, and the district lying a mile southwest. For many geologists, Slate 

Ledge Quarry has become the effective type locality, which overemphasizes the pelitic nature of the 

formation. The quarry is stratigraphically in the lower part of the Littleton, immediately beneath a 

persistent zone of felsic volcanic rocks and an unknown distance above the unexposed Fitch contact.

Conditions in the quarry have deteriorated over the years. The narrow entrance is hazardous. 

Loose rocks above could tumble down. Lichens and weathering obscure bedding and textures. We may 

decide not to gamble on entering the quarry and if we do enter, do not tarry in the entrance slot. Should 

we not enter the quarry, the spoil pile from the quarry is a short distance downhill across Slate Ledge 

Road. We are welcome to visit it.

Most of the quarry appears to consist of dark-gray slate. Sharp eyes may see thin graded beds 

with thin sandy or silty bottoms. Thin, pelitic turbidites probably make up a lot of the quarry. Numerous 

sandy bottoms are calcareous. Billings did not mention the calcareous bottoms, but did note the 

presence of diopside-clinozoisite-amphibole concretions in the high-grade Littleton. In thin section the 

slate contains tiny porphyroblasts of chlorite. Note the presence of fairly abundant pyrite, commonly in 

large cubes that are particularly abundant in the sandy bottoms of the turbidites. At higher metamorphic 

grade, where the iron sulfide is pyrrhotite, weathered Littleton is quite rusty and difficult to distinguish

from the Partridge Formation.

Bedding (N. 45o E.–85o E.) tops to the southeast. Cleavage dips southeast more gently than the 

bedding (N. 75o E.–75o E.), an observation also made on the roadside ledges we passed on the way to 

the quarry. The implied synformal axis to the northwest is hard to reconcile with the Walker Mountain 

syncline.

Continue southwest on Slate Ledge Road. Ledges, left, on the slope under the powerline are rhyolite 

conglomerate, breccia, and undivided volcanic rocks that constitute a mappable unit, including mafic 

volcanic rocks, in the lower part of the Littleton Formation in both the Walker Mountain and Salmon Hole 

Brook synclines. Some rhyolite conglomerates are matrix supported (dark-gray slate).

47.6 Bear left, uphill on Walker Hill Road.

48.2 Crest of Walker Mountain. Turn right on Grandview Road.

48.3 Beginning of loop road. Bear right and park on right side of road. This is Stop 7.

Stop 7. Sandy facies of the Littleton Formation (Dl)

Years ago we found fossil fragments in a float block of sandstone below the outcrop. Fossils 

were first discovered in the Littleton near the height-of-land on Walker Hill Road by Lahee (1912). 

Billings and Cleaves (1934) made more extensive collections from here and elsewhere on Walker 

Mountain and concluded an Oriskany (Pragian) age. Boucot in Boucot and Arndt (1960) re-examined 

these collections, made additional collections to the northeast on Dalton Mountain, and established an 

Emsian age for the type Littleton. Brachiopods from Beaver Brook suggest a slightly older age (Pragian) 

for the sillimanite-grade Littleton of the Moosilauke septum (Boucot and Rumble, 1980).

Regionally, as well as here on Walker Mountain, the Littleton becomes sandier higher in the 

section (Lyons and others, 1997). Most of this exposure is fine-grained feldspathic metasandstone with 

dark slate partings. Dark-gray slate is more prominent toward the road junction. Foliation is N. 40o E.–

75o W. Pyrite is abundant in cubes as large as 0.5 cm and commonly with quartz fibers growing in the 
16

pressure shadows. This is typical of the Littleton in the Walker Mountain syncline. No one has studied 

these. NO HAMMERS, PLEASE. Also, please do not remove fossils.

Continue around loop road (1.5 mi), return on Grandview Road, bear left on Walker Hill Road, and bear right on 

Slate Ledge Road.

52.1 Turn left onto N.H. 18/135.

54.4 Pass site of Stop 4 at east end of Moore Reservoir causeway.

54.6 Turn left on Partridge Lake Road at west end of Moore Reservoir causeway.

Lower Waterford 7.5-minute quadrangle.

55.3 Follow Partridge Lake Road around sharp right turn. Approximate unexposed contact between 

Ammonoosuc Volcanics (east) and overlying Partridge Formation (west).

55.4 Partridge Lake. Bear right and follow the narrow, twisting Partridge Lake Road around Partridge 

Lake.

55.6 Cross the unexposed Mesozoic (?) normal (down to the east) Ogontz fault: Oar west, Op east).

55.8–56.2 The road follow follows the Moore Reservoir fault, another Mesozoic normal fault, which is down to 

the east and mostly unexposed: Oar west and Op east. This is the same fault that we crossed at 

Exit 44 of I–93 (mile 37.5). This fault is probably a reactivated Paleozoic fault.

56.5 Road becomes Pond Road. Park in large open area just north of the Littleton-Lyman town line. This 

is Stop 8.

Stop 8. Rhyolite/mudstone debris flow interlayered with rhyolite aphanitic tuff and black slate

(Oar)

This exposure represents a transition zone between units Oap and Oar of the Ammonoosuc 

Volcanics. NO HAMMERS, PLEASE. The riprap below the guardrail east of the road offers abundant 

hand samples.

Most of the roadcut consists of laminated and bedded, tightly folded debris-flow material 

(“diamictite”) consisting of dark, tuffaceous pelite containing abundant clasts of light-gray tuff from 

vanishingly small pieces to interbeds of aphyric tuff several centimeters thick and less abundant black 

slate chips from vanishingly small pieces to interbeds of black slate. The diamictite also contains 

scattered feldspar and glassy quartz xenocrysts as well as less-deformed clasts of quartz-phyric and (or)

feldspar-phyric rhyolite. Clearly volcanism was contemporaneous with the deposition of black mud. 

Light-colored, slightly rusty weathering dolostone lenses are sparingly present. At the north end of the 

roadcut, isoclinal dextral folds of bedding (N. 25o E.–80o W.) plunge 70o to the southwest. Foliation is 

axial planar to the folds. The intersection of a poorly developed second foliation (N. 90o E.–70o E. ) with 

the regional foliation produces a penciling in the pelite and tuff and a pronounced lineation in the tuff.

When this roadcut was fresh in the year 2000, an 8-cm-thick bed of sideritic ironstone was 

exposed at the gentle curve concave-northwest about 450 ft south of the town line. Several thinner 
17

layers of the punky-weathering ironstone were also visible between here and the sharper road curve to 

the southwest.

56.65 Sharp curve to right. Strongly foliated and lineated rhyolite crystal (plagioclase) tuff of Oar.

56.7 Park on right side of road opposite sharp ridge on left. This is Stop 9.

Stop 9. Sulfidic black slate, Ammonoosuc Volcanics (Oap)

This is the eastern edge of a 2.4- by 0.3-km (maximum dimensions) lens of sulfidic, dark-gray 

slate (“cruddy black slate,” CBS) that lies west of the debris flow of the last stop. The slate is bounded 

on the west by felsic Ammonoosuc. We mapped the lens as a pelite unit, Oap, of the Ammonoosuc 

Volcanics but the rock is indistinguishable from the Partridge; the lens is shown incorrectly in figure 2 

as Op.

Continue south on Pond Road. 

57.7 Ledges of rhyolite of the Ammonoosuc on right behind gravel pit.

The road along Dodge Pond is interpreted to be in the Partridge Formation immediately southeast of the Moore 

Reservoir fault. One may legitimately ask: Why Partridge and not unit Oap of the Ammonoosuc?

59.0 Turn left on Lyman Road (paved).

59.05 Outcrop on right; Partridge Formation.

No roadside exposure for the next 1.3 miles but we cross various units of the Ammonoosuc Volcanics.

60.2 Cross position of the Ogontz fault: Oar on west, Op on east. 

60.3 Turn right on gravel Quebec Road (Stickney Road on topo sheet). Unexposed Fitch Formation.

The long uphill stretch of Quebec Road is mostly in the Fitch, with lenses of Clough conglomerate against the 

Ogontz fault.

61.5 Crest of hill.

Lisbon 7.5-minute quadrangle.

62.2 Quebec Road dead-ends at Clough Hill Road (Parker Hill Road on topo sheet). This is Stop 10.

Stop 10. Clough Quartzite and Fitch Formation

Billings (1935) proposed the name Clough Conglomerate for interbedded quartz conglomerate 

and quartzite that directly underlies the Fitch Formation. He (Billings, 1955, 1956) changed the name to 

Clough Quartzite to better reflect the dominant lithology. Billings does not designate a type locality, but 

takes the name Clough from the Clough Hill district, which is essentially where we are (figs. 1 and 2).
18

This outcrop is a large, magnificent, mostly pavement exposure of conglomeratic Clough 

Quartzite. The conglomerate is both clast-supported and matrix-supported and is poorly sorted. The 

clasts range in size to as much as 5 by 7 cm. They are mostly vein quartz but include gray slate and 

magnetite-bearing ironstone. We saw no granite clasts. Where clast-supported, the quartz clasts indent 

one another but otherwise are little deformed. Bedding is crude but a couple of graded beds (N. 40° E.–

80° E.) top to the east. Rhyolite followed by greenstone of the Ammonoosuc is exposed around the 

corner on Clough Hill Road to the west.

Walk east along Clough Hill Road 30 m or so. Calcareous siltstone of the Fitch Formation is 

exposed under the powerline. Bedding is N. 45° E.–85° E.; foliation N. 65° E.–85° N. We are on the 

slightly overturned limb of the Walker Mountain Syncline a little more than 10 km southwest of Slate 

Ledge quarry. 

Continue downhill to the southeast on Clough Hill Road. Roadcuts are absent for the next mile, but mapping shows 

that the section from Ammonoosuc to Fitch is repeated by faulting.

63.2 Exposure on right of the Littleton Formation. The repeated, unexposed Silurian section has an 

across-strike breadth of only 100 m.

64.1 Turn left on Cole Plain Road just after crossing the unexposed Mesozoic, west-dipping 

Ammonoosuc normal fault. Here the Littleton Formation of the Walker Mountain syncline (west) is 

downdropped against the Albee Formation (east).

64.6 The low ridge to the left is held up by the Fitch Formation and Clough Quartzite exposed in a fault 

slice along the Ammonoosuc fault. 

65.5 Cole Plain Road dead-ends into Lyman Road. Turn right on Lyman Road. The waterfall across from 

the intersection is held up by chlorite-grade Littleton Formation in the footwall of the Ammonoosuc 

fault. The fault (N. 65o E., 40o W.) is exposed in the streambed and near the gorge wall. Slickenlines 

trend N. 80o W. and plunge 30o W. Strongly sheared rhyolite tuff (Oar) of the Ammonoosuc 

Volcanics forms the footwall. Access to the exposure is treacherous.

65.8 Lyman Road dead-ends into U.S. 302. Turn left on U.S. 302.

66.4 Roadcut on left. Park on shoulder on right. This is Stop 11. WATCH OUT FOR TRAFFIC.

Stop 11 (optional). Ammonoosuc Volcanics 

Long roadcut exposing amphibolite (Oaa) interlayered with lesser amounts of metamorphosed 

rhyolite (not mapped separately) of the Ammonoosuc Volcanics. This is planned as a quick stop to look 

at mafic rocks of the Ammonoosuc (Oaa) at intermediate-grade, probably garnet, metamorphism east of 

the Ammonoosuc fault. An analysis of the amphibolite normalized, volatile-free and with iron reduced 

shows 49.21 weight-percent SiO2.

Turn around and head south on U.S. 302. Cross the Ammonoosuc River immediately south of Lyman Road.

66.9 Turn left on N.H. 117 toward Sugar Hill. The highway follows the valley of Salmon Hole Brook.
19

Sugar Hill 7.5-minute quadrangle.

Rocks exposed in Salmon Hole Brook between here and mile 67.4 include several rock types of the Ammonoosuc 

Volcanics as well as Partridge Formation, Clough Quartzite, and Littleton Formation of the Salmon Hole 

Brook syncline. The Fitch Formation does not crop out in this section along the brook.

68.4 Roadcut on left of Littleton Formation containing medium-size staurolite and small garnet 

porphyroblasts.

End of road log.

Return to Bretton Woods via Sugar Hill (spectacular views of the White Mountains), Franconia, I–93, and U.S. 3.

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20

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21

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