DEPARTMENT OF THE INTERIOR 

. FRANKLIN K . . LANE, Secr~tary 

UNITED STAT.ES GEOLOGICAL SURVEY 

GEORGE OTis SMITH, Director · 

Professional Paper 108~1 

STRATIGRAPHY IN SOUTHWESTERN M·AINE AND 

SOUTHEASTERN NEW H.AMPSHIRE 

BY 

FRANK J. KATZ 

Published December 13, 1917 

Shorter contributions to general geology, 1917 

(Pages 165-177) 

WASHINGTON 

GOVERNMENT PRINTING OFFiCE 

1917 
CONTENTS. 

Introduction •......... ... ... : ............... _ .. _ .............. _ ..... ~ .................................. . 

Area .............. - - -. --------- ----- ---- -------------------· · · · -: · · · · · · · --· - -· · · · · · · :-· · · · · · · · · · · · · · Field work ................. _-_ ..... . ... ... .. . ..... . . ..... . ... ~ .......... : ....... . .. , ..... ....... ... . Preyious work ............. _· . . ............ _ . _ . _ . _ . ___ . _ ·. _ . _ . ·_ :. ___ . ____________________ . ___ . _ . _ . ____ _ 

Stratigraphy .............................. .. . _ . _ . _ . _ . _ ... .. _ . _ . _ . _____ . __ .· ____ · _____ . __ . _ . . __ . ___ . ___ ___ _ 

General features ....... : . ........ . . ................... . ..... , ...... ~ .. . ..... ......................... . 

Sedimentary rocks .......... . ... .... ... , ............................... . ........................... ~ .. 

Pre-Carboniferous rocks ...... . ........ . ................... . ............................. _· ...... . 

Berwick.gneiss ..... · .................................. , ............................... ~ .... · .. 

Algonkian_(?) complex .................. .. .............. ·_ ............... _-_ .................. . 

Carboniferous rocks ........ ... _ .. .. ............ ...... ................ ~ ...... ... . .. . ............. . . 

Kittery quartzite •.......... .... ~ ..................... ~ ............................ . .. , .... . 

Eliot slate ......•........ ~ ........... • . . . ......... . ... .... -. -... -. ----------------------------

Casco Bay group .•..... .. .. ..... .' ............... ... , .. . . ·_ .... . ... · . . ..... . c •.•. ·_ ...•••••••• ••• 

General features ....... ...................... . . ....... .. ..... ........................ . . . . 

Cape Elizabeth formation ... ... .......... . ..... -.... ·_ .............. . ........ .............. . 

Spring Point greenstone ....... ·_ .. . ................... ... ................ ... · ........ ..... . 

Diamond Island slate ..... . ............. . .... .. . : .... ....... . ..... ....... . . ..... ...... . . 

Scarboro phyllite .. ...... ~ . ...... .... .............. . ... .... ....................... ·_ ..... . 

Spurwink limestone .. -.............. .... ...................... : ......................... . 

Jewell phyllite ............................ . ... ....... , . ......................... ~ ...... . 

Mackworth slate ......... . .. .. . . .... ....... ... .... ·_ ........ _· .................. -........... . 

Relations of the Casco Bay group .................. . ............... ~ ..... ......... : .... .. . 

Gonic formation . ... ...... .. ... ......... ... _ ....... ... .. , ........................ ... .. , .. _ .. 

Rirrdgemere formation: ......... ........ ~ ................................................ .... . 

Towow formation ..................................... . ............................. '........ . 

Stratigraphic relations and age of the Gonic, Rindgemere, and Towow formations ........... .... . 

Igneous rocks ................................... . ....... . ... . -. .. ..... _ .. . _ . ... : .................... . 

Westbrook granite and Falmouth pegmatite .................. , . .. ~ ............... : ..... ... ........ . 

Igneous rocks of the Algonkian (?) complex .............................................. -........ . 

Cushing granodiorite ................. _ ................ ..... .. ....... ....... ... .... . ............ . 

Altered basic dikes .. ." ............................................ _ ......... · . .... .......... . _·_ .. . 

Diorite in Saco .......... ........ ~. _ ............................ · ........ : .... ... ... .... ......... . 

Exeter diorite ....... , .............. ... ............... .. ........ . ....... . ..... ... ... . .. , . .......... . 

Biddeford granite ............................................................. .......... __ .... . 

Other granites ...... .... ........... ............... . .... ......... ... _._ .. ..... . ............. ..... . 

Trap dike.s ................ ~ ...... -: .................... ' ...... -..... -. -. --- --- - - . -- --- -. -. --- - --

ILLUSTRATIONS. 

Page. 

165 

165 

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166 

166 

166 

166 

167 

168 

168 

169 

170 

170 

170 

170 

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171 

171 

171 

172 

172 

172 

173 

174 

174 

175 

175• 

175 

176 

176 

176 

176 

176 

177 

177 

Page. 

PLATE LXI. Geologic sketch map of southwe~tern M~ine and southeastern New Hampshire.................. 168 

FIGURE 26. Index map showing area in southwestern Maine and southeastern New Hampshire................ 165 

II 
STRATIGRAPHY IN SOUTHWESTERN MAINE AND SOUTHEASTERN NEW 

HAMPSHI~E . .. 

By FRANK J. KATz. 

INTRODUCTION. 

Area.-The region discussed in this paper 

includes some 1,500 square miles, most of which 

is in the southwest corner of Maine, in Cumberland and York counties, the remainder being 

in the adjacent parts of Strafford and Rockingham counties, N. H. The area lies between 

67° 

__L_ -~(J---j43 

!.., ' 

\ r~ 

2~ 25 50 75 IOOMILES 

FIGURE 26.-Index map showing area in southwestern Maine and southeastern New Hampshire. 

meridians 70° and71 ° arid parallels 43° and 43° 

45', which inclose the Casco Bay, Portland, 

Buxton, Newfield, Biddeford, Kennebunkport, 

Berwick, York, and Dover quadrangles of the 

United States Geological Survey topographic 

atlas. _(See fig. 26.) -

100330°-17 

Field work.-The conclusions on this region 

here set forth are the result of wor~ begun in 

July, 1911, and still in progress. The field 

work has included critical study and detailed · 

mapping of about one-third of the area and 

reconnaissance examination of the remainder. 

This work was under the direction of Mr. Arthur 

Keith, who has conferred frequently in the 

field and office with the writer and whose 

encouragement and assistance contributed to 

its progress. Mr. Laurence LaForge, who has 

long · been studying areas in New Hampshire 

and Massachusetts soU:-:!}lwest of the region here 

considered, has also contributed to the results 

by field conferences and by critical discussions. 

The writer gratefully acknowledges indebtedness to both these geologists. 

Previouswork.-Little geologic work had been 

done previously in southwestern Maine and the 

adjacentpart of New Hampshire, and there are 

no published conclusions of present interest 

except those of Charles. H. Hitchcock/ which 

can be briefly summarized as follows: 

Hitchcock elaborated the views of his father, 

Edward Hitchcock, on the geology of the 

vicinity of Portland, Maine, and following him 

divided the rocks of the region on the basis of 

lithology into a number of varieties of schists 

and assigned them to his Huronian and Cambrian, or Paleozoic ( ~). Furthermore, he recognized these sedimentary rocks of the Portland 

and Casco Bay region as distinct from those of 

adjacent areas. The gneisses to the north and 

west of the Portland rocks he assigned to the 

"Laurentian or Azoic," but later he_ correlated 

part of these gneis~es with his Coos group 

(Paleozoic) _of New Hampshire. He further 

1 Hitchcock, C. H., General report upon the geology of Maine: Maine 

Board Agr. Sixth Ann. Rept., pp. 146-328, 1861; The geology of Portland 

(Maine]: Am. Assoc. Adv. Sci. Proc., vol. 2, pt. 2, pp. 163-175, 1874; The 

geology of New Hampshire, pt. 2, Stratigraphical geology; and atlas; 

Concord, N.H., 1877; Geology of northern New England (Maine, with 

map), 1885; The geology of New Hampshire: .Jour. Geology, vol. 4, pp. 

44-52, 1896. 

165 
166 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

-noted in York County, Maine, the continuation 

of his Merrimack slates ("flinty slates") of New 

Hampshire, and northwest of these in Maine 

and New Hampshire, in the vicinity of Rochester and elsewhere, he mapped and described the 

"Rockingham mica schists" and "Kearsarge 

group" (andalusite schists), both of which he 

stated to be more or less equivalent to his· 

Merrimack slates and related to the Huronian 

as well as the Cambrian but referred-doubtfully 

to the Paleozoic. The relation of Hitchcock's 

several subdivisions and his petrographic units 

. can not bereconciled with those of'the present 

paper. An attempt is made, howe.ver, by 

means of footnotes in the stratigraphic table to 

indicate so far as possible the correspondence 

of his subdivisions. · 

STRATIGRAPHY. 

GENERAL FEATURES. 

The region under discussion is a part of the 

New England coastal lowland, here a belt 10 to 

25 miles wide, whose rock surface is abundantly 

mantled with glacial drift and over broad areas 

deeply buried under outwash deposits, both 

terrestrial and marine, of late Pleistocene age.t 

This condition, with the further handicap th'at 

the sedimentary rocks so far as known are nonfossiliferous and are metamorphosed to an 

extent which makes · the discovery of fossils 

improbable, is a considerable hindrance to 

stratigraphic work. However, over a large 

part of the regipn outcrops are found at intervals short enough for positive correlation on the 

basis of pronounced lithologic characteristics, 

and furthermore, although the structure is 

complex in detail, the region shows a dominant 

and_simple major structure-that of elongated 

folds on approximatefy paralle~ northeast 

axes-which is of assistance in tracing and correlating stratigraphic units. The rocks include 

(1) an assemblage of more or less severely deformed and metamorphosed sediments, with 

which are associated some volcanic rna terials, 

and (2) a number of types of intrusive rooks, 

some of which also are metamorphosed. None 

· of the rooks have been sufficiently altered by 

mashing and recrystallization to lose their 

original character completely. 

1 Katz, F.'J'., and Keith, Arthur, The Newington moraine, Mairie 

N.H., and Mass.: U. S. Geol. Survey Prof. Paper 108', pp. 11-29, 1917 

(Prof. Paper 108-B). 

The differenti~tion of the sedimentary formations a~d their classification and mapping have 

been based upon recognition of t:t ·general and. 

characteristic lithologic facies for each formation, upon careful consideratio~ of their petrographic similarities and differences, upon 

cautious use of character and degrees of deformation and metamorphism as crit,eria, and upon 

areal di~tribution as interpreted in the light of 

distinguishable structure. Thus eight cartographic units have been recognized.. The igneous rocks are roughly grouped by means of 

their obvious petrographic features, areal distribution, and relation to the sedirllents. The . , 

resulting classification of the rocks and their 

stratigraphic relations and equivalences are 

shown in the accompanying table. 

The map (Pl. LXI), on account of its small 

scale and the lack of precise data in a large 'part 

of the area, is very much generalized as to position and minor features of the formation boundaries. Because of lack of outcrops the following 

parts are wholly arbitrary and inferential: 

The southwest termination of the Towow 

formation in Lebanon, ·Maine; the approximately north-south line which bounds part of 

the Berwick gneiss and ·cuts ·off the Carboniferous rocks in Rollinsford . and Somersworth, 

N. H.; and the line between the Casco Bay 

group and the Kittery quartzite in Biddeford 

and Saco, Maine. The igneous rocks are represented as continuous over some areas, and · 

their boundaries are drawn with solid and 

smooth lines where they'· have most irregular 

outlines and ·partly or wholly include large 

blocks of sediments. Furthermere, the relations of formations at contacts, whether of intrusion, faulting, conformable succession, or otherwise, are nowhere indicated by the character . 

of the lines on the map. With these exceptions, 

however, the map is presented with considerable assurance that it conforms generally with 

the facts. 

SEDIMENTARY ROCKS. 

PRE-CARBONIFEROUS ROCKS. 

BERWICK GNEISS. 

The Berwick gneiss, named from the town of 

Berwick, Maine, occupies a continuous belt in 

the central and northeastern parts of the region 

here discussed and extends both northeast and 

southwest for undetermined distances. The 
Carboniferous 

(Pennsylvanian(?). 

Pre- Carbonif- erous. 

For. .. tions in southwestern Maine and southeastern New HampBh'l>'re. 

Sedimentary rocks. 

Casco Bay group: a Mackworth s!ate: Qu.artzites and q~artz slates, 200 feet(?) .. Jewellr:hyl~tte: b SIIIC~ous and argillaceous slates and phyllites, 500 feet(?). 

Spurwtnk ltme~tone: Limestone and phyllites, 200feet (?). 

Scarboro phylltte: Black and gray argil- laceous phyllite, 200-600 feet. . Towow formation: Black carbonaceous 

Diamond Island slate: Black carbona- Elwtslate:c Gray quartz slate and phyllite, 200-300 

ceous quartz slate, 75-150 feet. slates, c~lc;a- ~eet (?). . Sprinp Point greenstone: Hornblende reou~ argillite Rt'ndgemere formatwn: d Dark-gray car- schists, etc., 0-600 feet. (lfadite), and bonaceous phyllites, slates, grayCaJ!e. Elizabeth formation: Graywacke, ~ ack phyl- w~cke, and_quartzite, 1,000 feet(?). 

siliceous slates, and argillaceous hte. Gon~c form_atwn:e Gray~acke schists, . slates and phyllites, 600 feet(?). miCaschists,andphylhtes, 500feet(?). 

Ktttery quartzite: I Quartzite, argillite, slate, and schist, 1,500 feet(?). 

Quartzites with rhyolite flows and tuffs; slates, schists, and hornblende schists; quartzite and graywacke 

gneisses of Algonkian (?) age.Y 

Berwick gneiss:h Graywacke gneisses and schists and quartzite. 

a C. H. Hitchcock's Huronian and Cambrian in the vicinity of Portland, except as indicated in note b. 

b Part of this formation in Saco is C. H. Hitchcock's Cambrian slate. c Included in C. H. Hitchcock's Merrimack slates. 

Triassic. 

Post- Carbonif- erous. 

Late Carboniferous(?). 

Unknown 

(probably 

pre - CarbonIferous). 

Unknown (postBerwick). 

d Approximately equivalent to C. H. Hitchcock's Kearsarge group in the vicinity of Rochester (a part of his Huronian and Cambrian or Paleozoic?). e Iricluded in C. H. Hitchcock's Rockingham schist (a part of his Huronian and Cambrian or Paleozoic?). 

Igneous rocks. 

Gabbro, diabase, and other 

dikes. 

Gneissoid biotite- muscovite 

granites and pegmatites in 

Milton, Lebanon, Acton, Sanford, etc. 

Biotite granites in Lyman, Alfred, Dayton, and Rochester. 

The assemblage in Mount Agamenticus; biotite granites, 

gabbros, and other differentiates in Wells, South Ber~ 

wick, and York. 

Biddeford granite: Mediumgramed biotite granite and 

/ pegmatite in Biddeford, Kennebunk, etc. 

Exeter diorite: Fine to medi urn grained light-gray diorite in 

Rollinsford, Dover, Newmarket, Exeter, etc. 

Medium io coarse, pariiy gneissoid diorite in Saco. 

Basic dikes. 

C u s h i n g granodiorite: Finegrained porphyritic gneissoid 

granodiorite. 

White(tourmalinic)pegmatites. 

Fine-grained muscoVIte granites. 

Coarse biotite granites, augen 

gneiss. 

Fine-grained diorite, etc. 

Westbrook granite and Falmouth 

pegmatite: Gneissoid biotite 

granite and white tourmalinegarnet pegmatite. 

I Included in C. H. Hitchcock's Merrimack slates and Rockingham schist (a part of his Huronian and Cambrian or Paleozoic?). g Included in C. H. Hitchcock's Merrimack slates. · h That part in New Hampshire and York County, Maine, placed by C. H. Hitchcock in his Merrimack slates and Rockingham schist (a part of his Huronian and Cambrian or Paleozoic?); that in the Portland 

region partly in his Laurentian or Azoic and partly in his Coos group or Paleozoic. 

100330°-17. (To face page 166.) 
,· 
I 

STRATIGRAPHY IN SOUTHWEST~RN MAINE AND SOUTHEASTERN N:EjW HAMPSHIRE. 167 

belt ranges in width from 2! miles at the south- toward the southeast on approxim~te parallel 

west, on the west side of the Dover quadrangle, northeasterly axes. ·.· In very small areas a few 

to at least 9 miles at the northeast, where it wide departures from the prevailing attitude 

occupies the northwest corner of the Casco indicate local intricacies in structure. 

Bay quadrangle, the northwest half of the Port- Along its southeast border the Berwick· 

land quadrangle, and the east half of the Bux- gneiss within this region is in contact with 

ton quadrangle. the Casco Bay group, with the partly equivaThe formation is composed chiefly of gray- lent slates in Dover, Madbury, and Lee, and 

wacke gneiss but contains also. clean quartzit~s, with the Kittery quartzite. Its north and 

micaceous quartzites, mica schist, and argillite northwest boundaries have not been deterschist and slate. The beds range from about an mined except in the Dover, Berwick, ' and 

inch to a few feet in thickness. Almost all the Kennebunkport quac!rangles, where it is adrocks are · moderately fine grained and deli- joined on the northwe.st by the Gonic forcately banded. . Their colors are medium to mation. Several bodies of massive granitic 

dark gray, bluish gray, and brown. In the and dioritic rocks are intrusive in the BerWick 

P_ortland · quadrangle a few layers, 1 to 3 and also cut younger fqrm~tio~s. In the 

inches thick, of light-blue and white crystalline northwestern part of the region there are 

limestone have been found. The most abun...: bodies of intrusive gneissic granite and pegdant and characteristic rocks are moderately matite, which are restricted to the area of the 

fine grained banded gray and bluish-gray gray- Berwick. Its greater deformation and more 

wacke or quartz-feldspar-biotite gneiss and complex structure, its notably greater metamicaceous quartzite~ Th~ formation is marked morphism, and the presence in it of deformed 

by a high degree of . crystallinity, by an a bun- intrusives not known to invade other for-

. dance of metamorphically developed biotite, mations show that the Berwick gneiss is older 

and in places by actinolite in graywacke and than the sedimentary formations which adjoin 

quartzite. Many of the beds are flecked with it. Evidep.ce is lacking to determine whet~er 

metacrysts of bl~ck biotite. The most dis- .the juxtapositions are due to unconformity or 

.tinctively characteristic alteration is a recrys- to faUlting. There are also no data on the 

tallization of the graywacke into nonfoliate · relative stratigraphic positions of the Berdiorite-like aggregates which contain chiefly wick gneiss ahd the other pre-Carboniferous 

quartz, feldspar, and hornblende and in some sediments. The age of the Berwick gneiss is 

places also garnet and which have the form of unknown. 

seam selvages or bands, lenses, and small spheroidal and irregular patches. On the northwest ALGONKIAN (l) COMPLEX. 

end of the belt, in parts of the Buxton, Port- In the southeastern part of the region a 

·land, and Casco Bay quadrangles and farther · greatly metamorphosed crystalline complex 

north, where this formation is heavily injected occupies a belt It to 4! miles wide trending 

by granite and pegmatite, it is metamorphosed northeast to east-northeast along' the coast 

to wholly crystalline quartz-biotite and quartz- in Gerrish Island, Maine, the islands in the ' 

feldspar-biotite gneisses of fine· t9 medium mouth of · Piscataqua River, New Castle, 

gra1n. and Rye, and parts . of Portsmouth, North 

The thickness of the Berwick gneiss is not Hampton, and Greenland, N. H. Among the 

determinable. stratiform rocks of this complex there have 

From the p~evailing northeast strikes, which been recognized fine-grained gray and whitish 

range, however, from nearly north to nearly quartzites associated with rhyolite flows and 

east, with dips generally moderate to steep breccias; see~ningly overlying dark-colored 

toward the northwest but in some places steep banded slate and Bchist, including abundant 

toward the southeast, and from intricate crum- hornblendic schist, which in turn appear to 

piing and close folding on northeasterly axes overlie medium to coarse grained micaceous 

discernible ·only in, some exposures of thin- quartzite and . graywacke. In these rocks the 

bedded members, the Berwick gneiss is in- cleavage is almost uniformly ver:tical or 

ferred to be closely folded and overturned has a very steep dip; it seems to be parallel 
168: SHORTER CONTRIBUTIONS TO GENERA~ GEOLOGY, 1917. 

to the bedding wherever that is discernible, 

and the strike of both cleavage and bedding 

swings from northeast on the south end of 

the belt to nearly east on the north end. 

All these rocks are intruded by large masses 

and interleaved with layers of a variety of 

granitic and some dioritic rocks, which are 

generally deformed and more or less foliated. 

The stratiform rocks of this complex lie in 

the general trend of the belt of outcrops· of 

presumed pre-Cambrian (Algonkian~) f~rmations, the Westboro quartzite and Marlboro 

formation of eastern Mass.achusetts,t and are 

very probably counterpar,ts .. of those formations. The areal relation&'and'the similarities 2 

in lithology and assoe:iation of ·the rocks in 

_ Rye and Portsmouth, N. H., to those of the 

Algonkian0) in eastern Massachusetts afford 

the basis for tentative assignment of these 

rocks in Maine and New Hampshire to the 

Algonkian. 

CARBONIFEROUS ROCKS. 

- lOTTERY QUARTZITE. 

The Kittery quartzite, named from the town 

of Kittery, Maine, in which typical exposures 

abound, occupies a 45-mile belt from Exeter; 

N .. H., to Saco, Maine. This belt is 7 to 13 

miles wide and lies along the coast, except for 

about 11 miles in the southeastern part, in 

Kittery, Portsmouth, Greenland, · Rye, and 

·North-Hampton, where pre-Carboniferous rocks 

intervene, and thence continues inland southwestward beyond ·the region here considered. 

Within this belt, especially along the coast, the 

exposures of the quartzite are practically continuous, being interrupted only by two very 

large and several small areas of granitic rocks 

and an area of slate described on pages169-170. 

Within the granite areas, particularly along 

their coastward sides, are many inclusions and 

large . engulfed blocks of. Kittery quartzite, 

which ·assist in establishing the continuity of 

the formation. · · . . 

This formation consists of banded flinty and 

vitreous quartzites, subordinate amounts of 

argillitic and micaceous quartzites, some argillite, and very thin beds of micaceous slate and 

1 Emerson, B. K., Geology of Massachusetts and· Rhode land~ 

U. S. Geol. Survey Bull. 597 (in press). 

2 Laurence LaForge, who has examined the rocks in both regions, 

has in personal communications reported these similarities. 

schist. .All these rocks are very fine grained. 

The formation is characteristically thin bedded, 

few of the beds exceeding 2 feet in thickness, 

and the thicker beds are generally marked par--

allel to the bedding by thin layers 9f different 

colors. The most striking feature of the formation is a fine interbanding of various tones of 

dark gray, bluish, chocolate-brown, and black 

with a little light gray E:tnd white. . On weathered surfaces there is an equally characteristic 

and more pronounced interbanding of white, 

drab, green, blue, and chocolate-broWn.. _ The 

dark-gray and brownish beds in particular are 

in many places banded, mottled, and intricately patterned in drab shades as the result of 

leaching and silicification, and argilli tic beds are 

commonly dotted with small variously colored 

spots.' The Kittery quartzite is only slightly 

metamorphosed; excppt in relatively few included thin beds of micaceous schist, recrystallization and foliation are weakly developed. 

Se.veral-exposures -of the Kittery quartzite 

show that it has been folded into a great number · of small open to ·moderately close rolling 

folds that trend northeast in most places buteast-northeast in Kittery and nearly east naar 

Biddeford Pool. Generally, however, the only . 

observable structure is a northeasterly strike. 

and vertical or high dips. Over small areas, 

notably near Ogunquit, Maine, and thence 

northward along the coast, and on Fox Point 

in Newington, N. H., there is considerable irregularity and departure from the normal strike 

and dips. The few data obtained along the 

west border of the granite in the Dover quadrangle indicate that the quartzite lies vertically 

against the granite or dips away from it. A 

few observations made in Portsmouth and 

Eliot along the east side of the Eliot slate (see 

p. 169) indicate that the quartzite dips toward 

(under) the slate~ _ 

No reliable measurement of the thickness of 

the Kittery quartzite is possible. The best 

estim.ate, made. at York Harbor, where .there is 

no evidence of repetition of beds, indicates a 

minimum of 1,500 feet at that place. 

The Kittery quartzite is bounded by diorite, 

granite, a:n,d gabbro, which intrude it; by the 

slate in Eliot, Newington, Dover, Stratham, and 

Exeter; arid the rocks of the Casco Bay group, 

which conformably overlie it; along most of" its 

northwest boundary by the Berwick gneiss, 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 108 PLATE LXI 

IGNEOUS ROCKS 

SEDIMENTARY ROCKS 

M.ackw-orth s1ate 

Jewell phyllite 

Spurw:ink limestone • CascoBay group 

Scarboro phy1lite i 

Cupe.Ehzabeth 

Dw.mond 

Spring Pomt 

Island 

greenstone 

formation 

slate j' 

Eliot 

~ 

~ 

slare 

Kittery quart7..ite 

orik:ian ~ ti'ICOlnple.x of r~(irke !!neiss, wrill>1 ndt' I:khist, qunrtzi .t·hrol it • nnrl wf 

rrrttn. tJ w e aro i7 ~<lnded 

p~yrnal''l~. granUe, dwrite, aJ.ldflf"(UUU gt te£.5~ 

~ 1. 

C<_'lle 375,000 

:-;::-.;:~~ 

":-;::-.;: "' "\·'"" ~~ 

Towow formation 

' 

' 

Rlnd~emere ormation 

~ 

Goni~ c fmmation 

Berwick gnei, , st=~~==~~=io============ 5============~1oM iles 

GEOLOGIC SKETCH MAP OF SOUTHWESTERN MAINE AND SOUTHEASTERN NEW HAMPSHIRE. 
STRATIGRAPHY IN SOUTHWESTERN MAINE AND SOUTHEASTERN NEW HAMPSHIRE. 169 

against which it is either faulted or is in unconformable superposition; ·and by the other preCarboniferous sediments, with which its relations,are unknown. The intrusive contacts are 

• exhibited and conclusively established in several exposures. _ The 9onformable relation of 

the overlying slate in Eliot and elsewhere is 

inferred from two facts-(1) the greater abundance of argillite in the Kittery quartzite ·near 

the exposures of Eliot slate in Eliot Neck and 

-in the vicinity of York River, which suggests 

transition of lithologic character from one to 

the other, and (2) the areal distribution and the 

apparent attitude of the quartzite with.relation 

to the slate. The quartzite surrounds the slate 

with approximately pttrallel strike and seems 

to dip toward it. The areal distribution of the 

quartzite and slate with respect to the granitic 

masses-that of successive surrounding belts~ 

also indicates the same relation. (See map, 

Pl. LXI.) For similar reasons the rocks of the 

Casco Bay group are inferred to overlie the Kittery quartzite, probably conformably, because 

the basal formations of that group are probably 

equivalent to the Eliot slate. · According to 

Mr. LaForge, outcrops across the Newburyport 

and Haverhill quadrangles, Mass., indicate that 

the belt of Kittery quartzite and overlying slate 

extends southwestward to . Merrimack River 

and is continuous with the Carboniferous Merrimack quartzite.1 The quartzite facies in the 

vicinity of Lowell, Mass., and in Kittery, Maine, 

are lithologically identical, but the Merrimack 

quartzite as defined and mapped in the work 

cited includes some slate and phyllite, which 

are very probably equivalent to those in the 

Eliot slate. , By correlation with the Merrimack quartzite, the Kittery quartzite and overlying slate are assigned to the Carboniferous 

period. , 

ELIOT SLATE. 

The - Eliot slate, named from the town of 

Eliot, Maine, occupies two parallel belts trending southwest through about 13 miles-one in 

Eliot and Kittery, Maine, and extending thence 

through Dover and Newington into Stratham 

and Exeter, N. H.; the otP,er in Dover, Madbury, Durham, and Lee, N. H. Both extend 

southwestward for undetermined , distances 

beyond the limits of the region here considered. 

-These belts are 2 to 5 miles and half a mile to 3 

1 Emerson, B. K., op. cit. 

miles wide, respectively, and are separated by 

a 3 to 5 mile belt of Kittery quartzite and intruded diorite. 

The rocks of both belts are identical in all 

respects, comprising an assemblage of gray 

sericitic and siliceous sericitic slates; beds of 

light-gray and drab argillo-quartzitic rocks, 

some of which are also calcareous; thin laminae 

of light-bluish limestone; .and thin layers of 

black carbonaceous sericite phyllite. Almost 

the whole formation is uniformly fine grained 

and thin bedded. In the central part of the 

eastern -belt, and presumably at the highest 

horizons in the formation, the black sericite 

phyllite layers are more abundant and thicker 

than elsewhere. 

The thickness of the Eliot slate is not determinable; there 'are no formations overlying it, 

and its top may be absent. 

The Eliot slate has the appearance of greater 

deformation and schistosity than the Kittery . 

quartzite, but this appearance is due to the 

fact that the formation is predominantly thin 

bedded and argillaceous; deformation has produced about the same degree of metamorphism 

in the Eliot slate as in the similar thin-bedded -

argillaceous rocks in the Kittery quartzite. 

The Eliot slate is somewhat_ less deformed 

structurally and less well recrystallized than 

the Casco _Bay group. 

Where discernible the strike of the bedding 

of the Eliot slate is almost uniformly northeast 

and the dip vertical or very high to the northwest; small folds pitch gently southwest. In a 

few areas there are easterly strikes indicating 

local folds. The structure of the eastern belt 

is inferred to be synclinal, the slate being infolded in the Kittery quartzite, as indicated in 

the discussion of that formation. 

The Eliot slate is in contact with the Berwick 

gneiss along a straight northeastward-trending· 

boundary of unknown structural significance; 

with a diorite by which it is intruded in Dover 

.and Exeter, N.H., and intervening towns; and 

with the Kittery quartzite, which it overlies 

conformably. It is therefore of Carboniferous 

age. The Eliot slate is correlated with the 

lower part of the Casco Bay group, more particularly with the Cape Elizabeth formation, on 

the basis of very close lithologic similarity, expressed not only in the colors, texture, and composition of the various rocks but also roughly in 

the proportions of each and the manner of inter-
. 4 

170 SHORTER CONTRIBUTIONS TO GENERAL . GEOLOGY, 1917. 

lamination of the thin layers of .black phyllite 

and calcareous beds. 'There is, however, a 

greater abundance of black phyllite in the upper 

part of the Eliot slate, ·which gives it an approach in character to the Scarboro portion of 

the Casco Bay group. Hence the 'Eliot slate 

does not appear to be preci~ely equivalent to 

the Cape Elizabeth formation but may repre ... 

sent also a part of the Scarboro phyllite. It is 

therefore given a separate name. · · 

CASCO BAY GROUP. · 

General features._:_The Casco Bay · group 

-derives its name from Casco. Bay, Maine, in and 

around which its parts are· well developed. 

The rocks of the group are limited ·in their distribution to the northeastern part of the region 

here considered, where they occupy: a compact 

area about 30 miles long and 12 miles wide, 

including the extreme northeast corner of the 

Kennebunk quadrangle, the north edge of the 

Biddeford quadrangle, the southeast half of the 

Portland quadrangle, and all but the northwest 

· corner of the Casco Bay quadrangle. From the 

central part of this area is excluded a strip, occupied by mtrusive granodiorite, some 16 miles 

long and as · much -as 3 miles wide, in Cape 

Elizabeth and the central islands of Casco Bay. 

The Casco Bay group has an aggregate thick-

:qess of 1,500 to 2,000 feet and consists of slate, 

phyllite, and schist, -dominantly of argillaceous 

origin; siliceous slate, graywacke, and quartzite; calcareous beds; and some greenstone and 

associated schist, probably of volcanic origin. 

-These rocks are divided into seven formations, 

as described below. . · 

Cape Elizabeth formation,-The Cape Elizabeth formation, the lowest unit in the Casco 

Bay group, is named from Cape -Elizabeth, 

Maine, where it is best and most~ completely 

exposed. The formation · crops out in many 

other places throughout the area occupied by 

the Casco Bay group. The Cape Elizabeth formation is an assemblage of mostly thin-bedded 

light-gray siliceous and sericitic slates, heavier 

beds of graywacke slate, schist, and quartzite, 

and it contains at short intervals thin layers or 

laminae of black n1icaceous phyllite and lightbluish calcareous schist or slate. Near High 

Head, on Cape Elizabeth, the lowest exposed 

parts contain about 10 feet of massive drab 

graywacke or quartzite, succeeded by 12 to 15 

feet of gray slate and sericite phyllite, with oaloare~us _laminae, followed by about ·the same 

thickness of gray ·sericite--quartz phyllite containing thin layers of blackish phyllite. Above 

these are thin layers of fine gray sericite-quartz 

slate iriterbe~ded with coarse-grained gray- . 

waoke·slate in beds 1 tQ 2 inches thick. These 

beds are succeeded by a considerable thickn.ess 

(not ·measuiable) tnade up chiefly of gray sericite·· slate and schist, which are finer grained, 

darker colored; and more mieaceous toward the 

top~ In other localities the formation contains 

beds of gneissic micaceous (biotite) quartzite, 

1 to 3 or 4 feet thick; · garnetiferous mica schist; 

and finely intermingled micaceous and siliceous 

schists. · The thickness of the Cape Elizabeth 

formation is difficult' to estimate but seems to be 

about 600 feet, whiohissuffioient to account for 

all exposures, for•ialthough they cover large 

areas the dips· are in the aggregate very low. 

Spring Point greenstone.-The Spring Point 

greenstone, which lies a_bove the Cape Elizabeth 

formation; is named from Spring Point, South 

Portland, 'Maine;.' :It is made up of gray to 

dark-green actinolite schist, in part thoroughly . 

schistose and in part somewhat massive; chlo.;.. 

ritic schists; ana some schistose rocks that still 

show j ·their'· origmal· coarsely ·and irregularly 

fragmenta.l texture and contain seoondary felts 

of small actinolite needles and small blebs ofblue quartz. In 'composition and texture the 

more ·massive phases resemble moderately 

mafic 'igneous rooks· and the schistose fragmental varieties resemble ·tuff, agglomerate,- or flow 

breccia. · The formation is very probably volcanic material locally but oonfonnably intercalated between the~' Cape Elizabeth formation 

and the Dianiondisland slate. Its distribution 

is not so wide :as that of the other formationsthat is, it is ·not found in aU places where its 

horizon is exposed but chiefly oniy in the cen:-

tral part of the Portland region in parts of Port:.. 

land, Bouth Portland, Cape Elizabeth, and 

southe~stern Scarboro. Its thickness is irregular but attains a maximum of probably 600 

feet'. 

Diamond Island slate.-The Diamond Island 

slate is named from Great Diamond Island and 

Little Diamond Island, in Casco Bay, where it 

is typically' exposed. It conformably _ overlies 

the Spring Point· greenstone but is more extensive than that formation aii.d also overlies 

directly the Cape Elizabeth formation in the 

northeastern part of Casco Bay and ill the 
STRATIGRAPHY IN -SOUTHWESTERN MAINE AND SOUTHEASTERN N-EW HAMPSHIRE. · 171 

southern part of Cape Elizabeth Township. 

The Diamond Island slate seems to be continuously developed in a tract 6! miles wide 

and 18 miles long within the region examined 

and to extend for an undetermined distance 

nor~heast; but the formation is not known 

and is seemingly not developed at its horizon 

in Richmond Island and in -the western part 

of the · area occupied by the Casco Bay group. 

The formation is made up in major part of a 

black pyritiferous, graphitic, and slightly 

micaceous quartz slate of very fine grain and 

in -lesser part of a black or bluish-black, somewhat graphitic and also pyritiferous quartzsericite phyllite. The rock is characteristically 

black and studded with small masses and 

crystals .of pyrite, which weather out on the 

surface 'of exposures and give rise to abundant 

copperas and rust . coatirigs. Equally characteristic of the Diamond Islarid slate are intricate 

crumpling on a small scale and an abundance of 

small crumpled quartz veins. Estimates based 

on width of outcrops where the beds are 

vertical indicate a thickness betw~e~ 75 and 

150 feet. --

Scarboro phyllite.-The . Scarboro . phyllite 

takes its name from _the town o'f Scarboro, 

Maine, in which it crops out abundantly, par-

. ticularly in the vicinity of Scarboro Beach, 

where the several 'phases of the phyllite are 

exposed. The Scarboro phyllite overlies the 

Diamond Island slate and the Cape Elizabeth 

formation. It consists of , uniformly fine.., 

grained sericite phyllite, for the most ·part 

dark bluish gray to black from the presence 

of biotite . and carbonaceous :matter, but 

locally light gray and white in the upper half 

of the formation. The rocks are typically not 

siliceous. .They are in places somewhat garnetiferous; and the dark-colored parts are in 

generalheavily impregnated with pyrite. The 

presence of vein quartz in chunky lenticles and 

irregularly contorted seams is characteristic, as 

are also knobby and undulatory rather than 

plane cleavage surfaces. Estimates of thickness based on width of outcrops of vertical 

beds indicate 200 to 600 feet. 

The Scarboro phyllite and Diamond Island 

slate are connected by rocks of intermediate 

and ·transitional lithologic type. In some 

sections both formations are present, the slate 

at the bottom; in other sections, in western 

Scarboro, Old Orchard, and Saco, the slate is 

absent. The phyllite is thus more widely 

distributed than the slate and may be regarded 

as overlapping on the Cape Elizabeth formation because of local failure of deposition of the · 

Diamond Island slate or a change from siliceous 

(Diamond Island) to argillaceous (Scarboro) 

sedimentation. 

Spurwinlc limestone.-The Spurwink limestone conformably overlies the Scarboro phyllite. It is named from Spurwink River, in 

Scarboro and Cape Elizabeth, Maine, whera it 

crops out. The formation is exposed in the 

eastern and southern parts of the Portland 

region but is probably also present under a 

heavy drift cover in the w:estern part. It is 

composed of thin in terlamina ted lenses of finegrained white and light-bluish crystalline limestone, fine-grained dark-gray calcareous mica 

schist, and fine gray siliceous mica phyllite. The 

layers· of pure limestone which preqominate in 

the lower and middle parts of the formation are 

f:r:om a small fraction of an inch to 2 or 3 inches 

'thick. The .gray phyllite bands of similar 

thickness are n1ore abundant in the higher 

than in -the lower parts and seem to dominate 

in the upper 50 feet. The formation is pyritiferous, in .places richly so. Weathering produces ribbed and rugose surfaces on the ledges 

and reddish .soils. Pefoimation has developed 

a characteristic intermingling of the fragments 

of disrupted limestone beds with the laminae 

of phyllite and' slate. The Spurwink limestone 

is about 200 feet_ thick. 

Jewell phyllite.-The Jewell phyllite conformably overlies the Spurwink limestone. It 

is named from Jewell Island, in Casco Bay, and 

is geographically coextensive with the Casco 

Bay group as mapped. The formation is an 

assemblage of .alternating gray and bluish to 

black fine-grained sericite phyllites in thin beds 

(a few inches to a few feet thick) containing 

also interbedded gray siliceous slate and very 

thin layers of quartzite. In some places the 

formation is dominantly light colored; in others 

it is dark, resembling the black-phase of the 

Scarboro phyllite. It is also like that for~ation in that its dark-colored parts ar.e in some 

places heavily impregnated with small grains 

and crystals of pyrite. However, the Jewell 

phyllite is distinguished qy the dominance o{ 

very fine grained medium-gray phyllite of silky 

luster and by the abundance in this rock of 

metacrysts, chiefly of garnet, but including 
172 ·. SHORTER CONTRIBUTIONS TO GENERAL · GEOLOGY, 1917. 

ottrelite, staurolite, magnetite, and other min- · but is not in visible contact with the Kittery 

erals, which commonly range from those of quartzite and -the Berwick gneiss. Farther 

minutely microscopic size to some measuring northeast the Jewell phyllite and Mackworth 

-an eighth of an inch. In some . places crystals slate are the areally marginal members of the 

of ottrelite and andalusite ( n an inch in length Casco Bay group and closely approach the 

are abundant. Berwick gneiss. The relation to the Berwick 

No relia~le measurement of the thickness of gneiss thus indicated is structural or strati- -

the Jewell phyllite is possible in view of the graphic · discordance (fault or overlap). By 

crumpling and repetition of the beds, but 500 correlation of the Cape Elizabeth formation 

feet seems more than ample to account for all with the Eliot slate the confo:..·mable superthe · outcrops, and the actual thickness may be position of the Casco Bay group on the Kitte~y 

much less 'than that. quartzite is indicated. This inference is supMackworth slate.-The Mackworth slate, -ported by the structure in the southwestern 

named from Mackworth Island, Casco Bay, part of the area occupied by the Casco Bay 

probably overlies the Jewell phyllite con- groJlp, where the rocks lie in a northeastwardformably. · It is the uppermost formation of pitching syncline and where the surrounding 

the Casco Bay group and is known only in and quartzite strikes east on the south side ar;d 

around the northern and northeastern parts of northeast on the northwest side of this syn- '--

of Casco Bay. The formation is composed of cline. The age of the Casco Bay group is 

quartzite and quartz-chlorite-mica slate in beds therefore Carboniferous. 

ranging from less than an inch to 2 or 3 feet in 

thickness. The rocks are dominantly siliceous 

and laminated and are characterized by abrupt 

alternations in lithologic character from flinty 

to chloritic slate. In color they range from 

white through drabs and light grays to dark 

grays and browns. Probably a thickness of 

100 fe~t is shown by the several exposures 

in and around Casco Bay. The top and 

whole thickness of the formation are unknown. 

Relations of the Oasco Bay group.-The metamorphism of the Casco Bay group is moderate 

and of the regional or dynamic type. It has 

resulted from the complex folding and intricate 

plication of its weaker -members. All its parts 

except the -nearly pure quartzitic beds are 

thoroughly . deformed, recrystailized, and 

foliate. -

In structure the Casco Bay-group is as a 

whole synclinal, _with a slight northeasterly 

pitch at the southwest end. I_n th~ longitude 

of Portland at least three secondary anticlines 

and two synclines are indicated, in which all 

. the formations are involved, and throughout 

the area there are many series of parallel minor 

folds that pitch northeast or southwest and 

involve one or several formations. 

- ·The area mapped as occupied by the Casco 

Bay group is bordered on the south and southwest by an area of Kittery quartzite and on the 

northwest by the Berwick gneiss. On the 

south and southwest the Cape Elizabeth format_ion, the lowest one of the group, approaches 

The Gonic formation, named.from the village 

of Gonic, N. :ij.; near which it is exposed, occu..: 

pies a so.:uthwesterly b~lt 2 to 6 miles wide and 

18 miles long from Sanford, Maine, to Barrington, N.H.· -This formation is made up ·of ar~naceous 

(graywacke) and argillaceous materials, metamorphosed to schist and phyllite, which are fo-r 

the most part rather thin bedded, fine grained, 

and whitish or light gray to dark gray. The 

rocks include mica schist and phyllite and interbedded fine to medium grained micaceous graywacke schists in beds as much as 2 feet thick; 

fine-grained light and dark gray -phyllites abundantly studded with dark staurolite crystals, 

some minute, others an inch or more long, or 

with red or brown garnets~ commonly in dodecahedrons about one-eighth to one-fourth inch in 

diameter, or with both minerals; and a little 

coarse muscovite schist·composed almost wholly 

of mica and very thin htminae of quartz. The 

beds of argillaceous origin that have developed 

into garnetiferous and staurolitic phyllites and 

mica-schist predominate, but the arenaceous 

beds (graywacke) are prominent. 

, The metamorphism of the formation is regional or dynamic and has progressed little furth~r and produced only slightly more general 

crystallinity than in the Casco Bay group. 

There is no evidence of significant contact 

metam?rphism, altho11:gh the granitie intrusive · 
STRATIGRAPHY IN SOUTHWESTER.N MAINE AND SOUTHEASTER.N NEW HAMPSHIRE. 17 3 

masses in the formation are large~ The de-

. velopmentof garnet and staurolite has no apparent relation to the granite. 

The beds of the Gonic formation are in general minutely crumpled, but folding on a large 

scale is not discernible. The strike is uniformly about northeast and the dip vertical or 

steep to the north west. · The thickness of the 

formation is unknown. About 100 to 150 feet 

of the coarser-grained phyllite and graywacke 

schist is shown in the hill northwest of Gonic 

village, and there may be two or three times as 

much in the rest of the formation. 

The Gonic formation is in contact on the 

southeast with the Berwick gneiss along a 

seemingly-straight line. The inferred relation, 

on the assumption of greater age of the -Berwick, is either fault contact or unconformable 

overlap. The northwest boundary of the belt 

of the Gonic formation, as drawn on the map, is 

a line between outcrops of rocks of dominantly 

Gonic type on the one side and of Rindgemere type on the'· other. The Gonic formation 

is intruded by biotite granite and pegmatite at 

both ends of the belt here considered. 

Discussion of the stratigraphic relations· and 

age of the Gonic formation follows the description of the Rindgemere and Towow formations. 

RINDGEMERE FORMATION. 

stone ·beds to dark bluish, gray, and black in 

the argillaceous beds. The rock varieties found 

in this region are light and dark gray micaceous 

slates and sericite phyllite associated with very 

fine grained micaceous graywacke schist, all 

abundari.tly speckled with small · to minute 

sporadic phenocryst-like minerals; :fine-grained 

gray ·sericite slate and phyllite which are pyritiferous and studded with chiastolite; interbanded light and dark gray and black carbonaceous quartz-sericite phyllites speckled with 

biotite flakes. and abundantly filled with large 

crystals of . chiastolite in the dark-gray and 

black bands; coarse mica schist. with chiastolite crystals measuring 6 to 8 inches by one-half 

to three-fourths of an inch; dark-gray ferrugi- _ 

no us chiastolite-bearing phyllite with which are 

interbedded dense quartzite and graywacke; 

and (in Acton and Shapleigh, Maine) some thin 

layers of white to bluish crystalline limestone. 

Andalusite artd chiastolite in large prismatic 

forms, in places with well-developed ''crosses," 

are abundant in ce;rtain -beds, notably in 

Rochester, 1! miles north of the center of the 

city, and in E.ast Rochester-, N.H., and on the· 

summit and upper east slope of Bauneg Beg 

Mountain in North Berwick, Maine. 

In the eentral part of the area occupied by 

the Rindgemere formation, and therefore, because of the structure, toward its top, the fine-: 

The Rindgemere formation is named from grained carbonaceous and argillitic sediments 

Rindgemere station (East Rochester), N. H., are the most abundant, although thin beds of 

on the Worcester, Nashua & Portland division quartzite and graywacke are present. At South 

of the Boston & Maine Railroad, at Salmon Lebanon, however, very near exposures of the 

Falls River. The formation is exposed in the Towow formation, · there ~s a zone of thincentral and northern parts of the Berwick quad- bedded light-gray slate and _quartzite. In the 

rangle in an area at least 12 miles wide and 15 outlying parts of the _area, as in the northeast 

- miles long. On the northeast it is cut off by corner of Rochester and the eastern part of 

granite and gneiss in Sanford and Acton, Maine, Lebanon, and therefore near the base of the 

and it extends southwest from Rochester, N.H., Rindgemere formation, quartzitic and grayfor an undetermined distance beyond the region wacke ·beds are dominant; but as a whole the 

examined. Within this area it surrounds a Rindgemere is made up dominantly of argilbelt 3 miles wide by 10 miles long occupied by laceous and somewhat carbonaceous rocks. 

the Towow form.ation, described below. The incomplete sections afforded by isolated 

The rocks of the Rindgemere formation are outcrops provide no basis for a measurement 

slate, phyllite, · and schist derived from some- of thickness. Several hundred feet is indicated 

what carbonaceous shale and argillite, with for each of the different · rock facies in East 

subordinate amounts of interbedded argilla-- Lebanon, East Rochester, and North Rochesceous quartzite, graywacke, and limestone. ter. The aggregate thickness of the formation 

They are generally thin bedded-few beds ex- is therefore considerable and may be about 

ceed ;2 -feet in thickness-and fine grained. 1,000 feet. 

The colors range from white and light gray or The data on the structure of the Rindgemere 

bluish in the quartzite, graywacke, and lime- formation in the Berwick quadrangle are 
174 SHORTER CONTRIBUTIONS TO GENERAL GEOLQGY, 1917 • . 

meager. T4e oqserved strikes are, in general, mation were seen near its contact with the 

northeast, with high northwest or vertical dip, Rindgemere .formation ~nd are therefore at the 

except between Rochester and West Lebanon, base ·of the Towow. ' The top of the Towow 

where . th~re. i~. an easterly strike .. and a lower formation is presumably· not present, and no · 

~ip, thus indic.ating ,a large major.syncline,in-: overlying formations are kn~Wn.. 

closing the elongate -oyal ,ar(:)a of the Towow There is no means of determining the thickformation. Another fold .of considerable. size ness of the part of the formation present in this 

is. suggested by the west-northwest strike arid region, b11:t it seems to be a few hundred feet. 

high northwest dip in East Lebanon, and many . The beds of tlie Towow formation are severely 

subordinate folds are shown by crumpling of crumpled, and the formation as a whole is probthe beds. Northwest dips in the hill 5_ nlj.l~~ ably intricately folded. Its relation to the · 

north of Rochester suggest that the · major Rindgemere formati()n indicates that the 

syncline may be overturned to the southeast. Towow formation here lies in the trough of a 

The Rindgemere formation surrounds the large syncline, whose east end is split by a $ecTowow forn1ationareally and is in contact with ondary anticline that pitches southwest . 

. the Gonic formation along an_ approximately 

straight northea.."t line on the southeast. The 

northern, northeastern, and northwestern limits of the Rindgemere have not been determined, because in those directions numerous 

1 masses of granite and pegmatits have disrupted 

an~ extremely metamorphosed . the sediments, 

so that their delineation is not yet possible-. 

Besides these intrusives on the border of the 

mapped area of the Rindgemere formation there 

are gra~i~i~ intrusives in North Berwick, Ma!ne, 

and in Rochest_or, N. H. .. · 

Discussion of the strf}tigraphic relations and 

age of the Rindgemere formation follows the 

description of the Towow formation. 

TOWOW FORMATION. 

The name of the Towow forrnation is derived 

from the original name of the first settlement 

in. the town of Lebanon, :Maine. The formation has been found only within that town, 

where it occupies a northeasterly belt about 

10 miles long and 2 to 3 n1iles wide. It is cmnpQsed of unifoirnly very fine grained and thinbe<Jded dark-gray to black carbonaceous or 

graphitic siliceous slates and s~ricitic slate or 

phyllite~ Except for some light-gray siliceou~ 

sericitic slate in North Lebanon and South Lebanon ~p.d for some interbedded layers of lightgray quartzite afew inches thick in South Lebanon, the fornlat,ion is rich)y carbonac;e~~ms and 

in places graphitic and is in1pregnated with 

-. pyrite in sn1all individual crystals and lenticular masses. These rocks are lithologically 

identical with the Diamond Island slate and 

the black pyritiferous part of the Scarboro 

phyllite of the Casco Bay group. The lightgray and quartzitic phases of the Towow forSTRATIGRAPHIC RELATIONS .A'ND .AGE OF THE GONIC, 

RINDGEKERE, AND TOWOW FORKATIONS. 

The Towow formation is surrounded by the 

Rindgemere formation, which occupies the area 

between the T()wow and Gonic form~tions. 

Between these .three formations there are intermediate or transitional phases, and all three 

show a general lithologic · similarity in bejng 

dominantly fine grained and thin bed.ded and 

containing .an abundance of argillaceous :qtaterial. They are, furthermore, allied by · a content of fine carbonaceous-matter, inconspicuous in the Gonic formation but increasing to 

abundance in the Rindgemere formation and 

to dominance in the Towow formation. They 

are ! structurally conformable and show no _ 

di~erences in aegree of metamorphism between beds of similar character. For these 

reasons and, furthermore, because there are no 

da~a to indicate the'contrary, they are assumed 

to form a stratigraphically conformable succession, of which the Gonic, on the basis of the . 

structural data present, is the lowest and the 

To.wow the highest. · 

These formations are assigned to the Carboniferous .period and are approximately equivalent to the lower formations of the Casco Bay 

group-the Cape Elizabeth, · Diamond Island; 

and Scarboro-and so also to the Eliot slate 

and to the Carboniferous Worcester phyllite 

in the Worcester Basin, Massachusetts~ This 

correlation rests on the following considerations: 

(1) The Towow formation and the J?iamond. 

Island slate are of identical character. (2) The 

three groups correspond closely in lithologic 

facies---that is, all three contain basal thin 

interbanded gray arenaceous (graywackf) and 
• 

. . 

STRATIGRAPHY IN SOUTHWESTERN MAINE ' AND SOUTHEASTRRN NEW HAMPSHIRE. f7 5 

a:r:gillaceous beds with abundant black carbonaceous laminae, succeeded by incr~asingly argillaceous beds, which in turn are followed by 

black carbonaceous arid pyritiferous siliceous 

slates and sericite phyllite . . Furthermore, the 

data on the thickness of the several members and 

formations, though not sufficient to · establish 

close resemblance, nevertheless indicate coniparable thicknesses 'or at least measurements 

compatible with the argument for correlation. 

Thus the maximum aggregate thicknesses of 

the formations compared are about 1,300 and 

1,800 feet, of both of wh.ich the far larger parts 

are in the lower arenaceous and gray argillaceous members and much smaller parts in the 

black carbonaceous slates. (3) Similarity in 

structure and in type and degree of metamorphism indicate identical history for both. (4) 

In lithology, deformation, and metamorphism 

these formations are similar to a formation of 

Carboniferous age (Worcester phyllite) in the 

Worcester Basin, described by Emerson. 1 Mr. 

Keith and Mr. LaForge 2 report that these 

formations of the Worcester Basin extend 

northeastward into New Hampshire within 30 

miles of Rochester, in a belt trending approximately toward the area of the equivalent Eliot 

slate. They are on the northwest side of a 

belt of graywacke and other gneisses that Mr. 

LaForge 2 reports to ·be, in part at least, continuous with and equivalent to the Berwick 

graywacke gneiss, which is in similar relation 

to the Gonic formation. 

IGNEOUS ROCKS. 

The relations of the igneous rocks of this 

region to the surrounding sediments have been 

determined so far as opportunity for field o bservation permitted. Very few of the igneous 

rocks have yet been studied petrographically. 

The following statements are made merely to 

point out _the areal distribution of the larger 

associated groups of igneous rocks and. to indicate roughly their stratigraphic relations. 

Westbrook granite and Falmouth pegmatite.-

In West brook, Falmouth, ·and Portland, Maine, 

granite and pegmatite intrude the Berwick 

gneiss and, so far as is known, are restricted 

to the northeast part of the gneiss belt. These 

1 Emerson, B. K., Geology of Massachusetts and Rhode "island: U. S. 

Geol. Survey Bull. 597 (in press). · 

2 Personal communications . 

rocks are named the Westbrook granite and 

Falniouth pegmatite, after the towns in which 

they are well developed and exposed. 

The West brook granite protrudes through 

the Berwick gneiss in a number of bodies 

elongated in northeaSterly and northerly 

directions and ranging in size from those 

that are very small to some 5 miles or more 

long and 2 or 3 miles wide. · It is a gneissoid 

granite of medium-gray color and fine, even 

texture and contain!' conspicuous crystals of 

biotite. Its essential components are microcline or orthoclase, quartz, oligoclase, and 

biotite, named in the order of abundance. 

Some very small masses of gneissoid granodiorite and diorite are included with the Westbrook granite. 

The Falmouth pegmatite occurs as . dikes' 

ranging from about an inch to many hundred 

feet in thickness and from a few feet to 3 or 4 

miloo in length. They are generally parallel to 

the northeasterly trend of the gneiss, although 

some of the smaller dikes transect or irregularly 

invade the gneiss they intrude. The Falmouth 

is a normal medium to very coarse grained 

pegmatite composed of perthitic microcline, 

quartz, muscovite, and albite, in places carrying 

abundant crystals of black tourmaline and red 

garnet. With it is associated a fine~grained 

white or light-gray garnetiferous apliter The 

pegmatite and aplite in many places have diffuse 

contacts with each other and with the Westbrook granite, indicating transition or intimate 

relation between them, although theW est brook 

granite is cut by the pegmatite and aplite and 

is very evidently somewhat older. Some of 

the larger pegmatite dikes in Falmouth have 

been slightly crushed. 

The age of the West brook granite and Falmouth pegmatite is. post-Berwick and presumably pre-Carboniferous, because they are not , 

known to intrude the . near-by rocks of the 

Casco Bay group. 

Igneous rocks of the Algonkian ( ?) complex.-

An assemblage of igneous roc~ restricted in 

distribution to' the area of the Algonkian ( n 

complex includes chiefly several varieties of 

fine to medium grained, evenly granular and 

porphyritic pink or buff-colored muscovite 

granites which are generally free of or deficient 

in biotite. They are very commonly gneissoid 
176 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1911. 

in texture. The series also includes fine- referred to the Maokworth slate. The visible 

grained dark-gray diorite, a gneissoid coarse contacts are so badly mashed and recrysta1-

porphyritic biotite granite (augen gneiss), and lized that the intrusive nature there indicated 

a very coarse white feldspar-quartz-muscovite is not decisively shown. This· nature is, howpegmatite which in places contains black tour- ever, further indicated by transgression of·the 

maline and some of which is crushed. · The bedding of the formations and by the aplite-

-small masses of granitic rocks and the pegma- like border facies. · The Cushing granodiorite, 

tites very closely parallel the trend of the sedi- though yolinger than the Carboniferous Casco 

mentary bands and are injected along the Bay group, is not improbably late Carbonifcleavage. Larger m:;tSses are ·elongate and erous, because it is older than undeformed 

have the same or approximately the same post-Carboniferous granite, which in: turn is 

trend, as the result of injection along the beds older than supposed Triassic. dikes. · (See 

or of infolding with them, or probably hoth. below.) 

Except that they are presumably pre- Altered ba..~ic dikes.-A considerable number 

Carboniferous, because they do not invade _of small black and dark-green dikes of basic 

the Kittery quartzite, the age of these intru- rocks (all less than 10 feet wide) are abundant 

sives has not been deterniined. However, a in _ the rocks of the ·casco Bay gro.up and the 

small body of white or buff fine-grained mus- Cushing granodio1_:ite. They are now severely 

covite granite and aplite that intrudes the altered schistose biotite-hornblende and hornKittery quartzite at Brave ·Boat Harbor, blende-garnet rocks. They may be c!osely 

though not deformed, is otherwise not unlike related in age to the Cushing granodiorite. 

some of the fine muscovite granites in Rye . Diorite in Saco.-The diorite in Saco, Maine, 

and New Castle. This rook at Brave Boat is an irregular elliptical body about 3 milesHarbor makes .the assignment of the similar long and 1! miles wide. The rock is medium 

rocks in Rye and New Castle doubtful. to dark gray, moderately coarse grained, and in _ 

Gushing granodiorite.-The Cushing grano- some places massive, in others gneissoid; it is 

diorite, named from Cushing Island, in Casco composed essentially of orthocla~e (~),andesine, 

Ba.y, occupies a single northeasterly belt hornblende, biotite, and subordinate amounts of 

extending for 16 miles from Scarboro, Maine, · quartz. This ro_ck invades the Berwick gneiss 

across Casco Bay to the northern lin1it of the and the Kittery quartzite and is therefore 

region here discussed. It is narrow at its post-Carboniferous. An argillaceous quartzite 

ends and has a maximum width of about 3! in contact wit~ the diorite is slightly altered 

miles. The granodiorite is thoroughly gneiss- to a rock somewhat like hornfels. 

oid, of light ,to dark gray color, and for the Exeter diorite.--The Exeter diorite, in Exeter,. 

most part finely and evenly but only slightly Newmarket, Durham, Madbury, Dover, and 

porphyritic in texture. Its principal com- Rollinsford, N~ II., occupies an area 15 miles 

ponents are albite-oligoclase as phenocrysts long and from half a mile to 5 miles wide. 

and quartz, feld~par, biotite, and hornblende The small area of diorite in Greenland_, N~ H., 

in the groundmass. Muscovite · or sericite, is a similar, and probably related rock. The 

probably all of secondary origin, is abundant, rock is a generally even, medium-grained iight 

but in proportions - differing from place -to to medium gray hornblende-bjotite diorite or 

place. Along part of the northwest · border quartz diorite, which changes in composition 

there is a white aplite-like facies. In places considerably but gradually fron1 place to place. 

toward the southwest end of the belt the In Newmarket, N. H., both aplitic and basic . 

granodiorite is dark gray, very biotitio, and vari~ties are present. These dioritic rocks are 

richer in hornblende ,than elsewhere. At the intrusive in the Kittery quartzite and Eliot 

northeast end it is very light gray and deficient slate and are therefore post-Carboniferous. · 

in biotite.· Biddeford granite.~The Biddeford ·granite, 

The Cushing granodiorite is infolded in and -in Biddeford, Kennebunkport, Kemi.ebunk, 

deformed with the . rocks of the Casco Bay and Dayton, Maine; is a generally even or 

group. It is known to be in contact chiefly slightly · porphyritic medium-grained biotite 

with the Cape Elizabeth formation but also granite of light-gray or 'pinkish-buff color, 

with the Jewell phyllite and rocks doubtfully composed of white microcline or orthoclase, 
STRATIGRAPHY IN ~OUTHWESTERN MAINE ANI) SOUTHEASTERN NEW HAMPSHIRE. 177 

quartz, oligoclase, biotite, and in some places 

also a little 1nuscovite. A few very small 

dikes of pegmatite and aplite are associated 

with it. The rock is intrusive in the Kittery 

quartzite and is post-Carboniferous. 

Other granites.-The granitic mass in Wells, 

York, South Berwick, and Eliot, Maine, is an 

assemblage, including chiefly a granite of the 

Biddeford type and several more mafic 

varieties, probably differentiates, among which 

are the gaboros of Cape Neddick and South 

Berwick. These rocks are intrusive into the 

Kittery quartzite and are of post-Carboniferous 

age. 

The granite in Rochester, Dover, and Barrington is generally a fine or medium and evengrained · but in places somewhat porphyritic 

and moderately coarse grained biotite-muscovite granite containing orthoclase and plagioclase and in places garnetiferous. In it a:re 

abundant large bodies of coarse pegmatite, COJfsisting of microcline, quartz, muscovite, and 

albite. 

In North Berwick, Maine, there is a small 

body· of very fine grained muscovite-biotite 

gTanite surrounded by and probably intrusive 

into the Rindgemere formation. It is, therefore, probably post-Carboniferous. 

The large area of granitic · rocks in Lyman, 

Alfred, Sanford, and Shapleigh, Maine, contains 

many included patches of gneiss (metamorphosed sediments) · and a variety of granites, 

the most conspicuous of which are large 1p.asses 

of granite of the Biddeford type; some quartz 

diorite, composed of oligoclase, biotite, quartz, 

dark hornblende, and magnetite; and somewhat gneissoid coarse-grained biotite-musco- · 

vite granite, with which is associated abundant 

coarse pegmatite. These rocks are intrusive 

in the Berwickgneiss and the Gonic and Rindgemere formations and are post-Carboniferous. 

The assemblage may include also some older 

but as. yet unrecognized granitic rocks. 

The areas of granitic rocks in Milton, N. H., 

and Acton and Lebanon, Maine, shown on the 

map, are occupied chiefly by medium to coarse 

grained gneissoid muscovite-biotite granites 

and coarse pegmatite. Included with these 

are various other granitic rocks and many 

patches of metamorphosed sediments. 

Trap dikes.-Throughout this region there 

are large numbers of small to moderately large 

trap dikes, for the most part of fine-textured 

gabbroic, diabasi:c, or doleritic habit. A few of 

the larger dikes are coarse grained, and many 

are in part glassy. They have been observed 

in all the other rocks of the region and many are 

themselves cut by others. ·Most if not all of 

them are younger than the post-Carboniferous 

·granitic intrusives and are tentatively correlated with the Triassic eruptions of Nova 

Scotia and southwestern New England. 

0