Boston to Buffalo, in the Footsteps of Amos Eaton and Edward Hitchcock: Boston, Massachusetts To Washington, D.C. June 28-July 8, 1989

109 Pages·25.906 MB·English

Boston to Buffalo, in the Footsteps
of Amos Eaton and Edward Hitchcock
Boston, Massachusetts to Washington, D.C.
June 28-July 8, t 989
Field Trip Guidebook Tt69
Leaders:
John Rodgers Thomas Grasso William M.Jordan, Editor
Associate Leaders:
Christopher Hepburn Edward S. Belt
Markes E. Johnson Gerald M. Friedman
American Geophysical Union, Washington, D.C.
Copyright 1989 American Geophysical Union
2000 Florida Ave., N.W., Washington, D.C. 20009
ISBN: 0-87590-652-4
Printed in the United States of America
COVER Portraits of Amos Eaton and Edward Hitchcock.
Leaders:
John Rodgers
Kline Geology Laboratory
Yale University
New Haven, CT 06551
Thomas X. Grasso
Geoscience Department
Monroe Community College
Rochester, NY 14623
William M. Jordan
Department of Earth Sciences
Millersville University
Millersville, PA 17551
Associate Leaders:
Christopher Hepburn
Department of Geology and Geophysics
Boston College
Chestnut Hill, MA 02115
Edward S. Belt
Department of Geology
Amherst College
Amherst, MA 01002
Markes E. Johnson
Department of Geology
Williams College
Williamstown, MA 01267
Gerald M. Friedman
Rensselaer Center for Applied Geology
P.O. Box 746
Troy, NY 12181
IGCFIELDTRIPT169:
BOSTONTOBUFFALOINTHEFOOTSTEPSOF
AMOSEATONANDEDWARDHITCHCOCK
WilliamM.Jordanl,Editor
GeraldM.,Friedman2,ThomasX.Grass03,JohnRodgers4
EdwardS.Bel~,MarkesE.Johnson6,RichardS.Naylor7
GENERAL INTRODUCTION
JohnRodgers
YaleUniversity,NewHaven,Connecticut
In 1824, Amos Eaton (1776-1842) published a "Geological Class included basalt and trap, and Eaton suspected theywere
ProfileextendingfromtheAtlantictoLakeErie"inthepamphlet volcanic.) Asaresult,therocksinMassachusettswereassigned
"Ageologicalandagriculturalsurveyofthedistrictadjoiningthe tothePrimitiveClass,exceptforSecondaryrocksintheConnec
Eriecanal,inthestateofNew-York"(Eaton,1824).Theproftleis tieutRiverbasinandTransitionrocksnearBostonandWorcester
over four and one-half feet long (1.4 meters); it displays the butthosealongtheErieCanalinNewYorkStatewereregarded
geologyfromBoston,Mass.,viaAlbanytoBuffalo,N.Y.,asEaton asTransitionorSecondary. AccordingtoEaton,theSecondary
understood it. The present excursionis designed to follow ap- formedonlysmallunconformablepatches(mainlyoffossiliferous
proximatelythelineofthatprofileandtoshowsomeofthesteps limestone) in the eastern third of the state but became more
bywhichourknowledgeofthatgeologyhasevolvedintheinter- important west ofLittle Falls (at least along tJ,e canal), where
vening165years. significant salt deposits were already known near Syracuse;
The1824profilewasnotEaton'sfirst;in1818and1820hehad Saliferousstratawere thenconsidered a hallmarkoftheSecon
published a section from Boston to south-central New York dary.
(Eaton, 1820),andin1822hepublisheda "GeologicalProfileof Theconceptofusingfaunalsuccessiontodatestrataappears
the rocks from OnondagaSalt Springs N.Y. [nowSyracuse], to tohavearrivedintheUnitedStatesbefore1820(e.g.,Say,1819,p.
Williams College, Mass."; parts ofthese proftles run somewhat 382). In1829LardnerVanuxem(1792-1848)usedittodistinguish
farther south than that of1824, but theyarebased on the same Secondary(Cretaceous)andTertiarystratainwhatMaclurehad
(Wernerian) stratigraphic principles. In the 1824 publication, calledAlluvialintheAtlanticCoastalPlain (Vanuxeum,1829a),
Eatonalsopresenteda sectionacross mostofMassachusettsby and to show that what Maclure had called Secondary in the
EdwardHitchcock(1793-1864),withsomeaccompanyingnotes, westernstateswasinfactTransition(thatis,Paleozoic;Vanuxem,
although Hitchcock had not authorized its publication and was 1829b). Thevalueofthe conceptwasfullydemonstratedbythe
somewhatputout(lettertoBenjaminSilliman,28May1824,Gratz geological and paleontological work of the New York State
collection,HistoricalSocietyofPennsylvania),forHitchcockhad Geological and Natural History Survey of 1836-1842, ofwhich
done little work in eastern Massachusetts at that time. Eaton Vanuxemwas the seniorgeological member; two others ofthat
evidentlymadesomeuseofHitchcock'ssectioninpreparinghis_group, Ebenezer Emmons (1799-1863) and James Hall (1811
own, but Eaton mentioned several differences in nomenclature 1898), were·former students ofEaton and later his junior col
andheincorporatedsomedetailsfromhisownearlierprofiles. leaguesat theRensselaerSchoolorInstitute. Thegeologistsof
AtthistimeEaton,likeHitchcockand,beforethem,Maclure theNewYorkSurvey(seetheirfinalreports: Mather,1843;Em
(1809),usedaterminologybasedontheWerneriansystem,though mons,1842;Vanuxem,1842;Hall,1843;alsotheirannualreports
EatonandHitchcockbothacceptedHuttonianviewsontheorigin from1837to1841andthoseofTimothyConrad) usedseveralof
ofigneousrocks. EatonassignedtherockstoPrimitive,Transi- Eaton'srocknam~s.(such as "CC!.lciferoussan4rock", a termnot
tion, Secondary, Superincumbent, (of Bake\vell), and Alluvial replacedbya lo~tyname until 18~),but from the frrst they;
Classes,onthebasisofmineralogicalcomposition,attitudeordip d~pendedonfossilstoorderand.classifyt~estrata. Vanuxemand
oflayering and degree ofconsolidation. (TheSuperincumbent his colleagues corrected the DllScorrelatIons that had resulted'
, fromEaton'stooconfidentrelianceonsuchrocktypesassalt,and
theyshowedthathisTransitionandSecondaryrocksinNewYork
State were all part ofa single great system ofstrata, which, at
Emmons' suggestion, theynamed the New-York System or the
1MillersvilleUniversity,Millersville,Pennsylvania
New-York Transition System. Eaton's supposedly unconfor-
2RensselaerCenterforAppliedGeology,Troy,NewYork
)mabiepatchesofSecondaryrocksweresimplymorefossiliferous
andBrooklynCollege,CityUDiversityofNewYork
layersinthegeneralsuccession;hisSaliferousstratawereasub
3MonroeCommunityCollege,Rochester,NewYork
ordinateunitintheNew-¥'orkSystem.
4YaleUniversity,NewHaven,Connecticut
At the same time that the NewYork geologistswere estab
5AmherstCollege,Amherst,Massachusetts
lishing the New-York System, the Rogers brothers, Henry D.
6williamsCollege,Williamstown,Massachusetts
Rogers (1808-1866) asStateGeologistofPennsylvaniaandWil-
7NortheasternUniversity,Boston,Massachusetts
T169: 1
liamB.Rogers(1804-1882)asStateGeologistofVirginia(includ theBerkshire-GreenMountainsaxisinwesternmostNewEngland
ingpresent-dayWestVirginia),wereworkingoutthestratigraphic wereespeciallyconfusingandgaveagooddealoftrouble. Eaton's
sequenceofthePaleozoicrocksinthefoldedAppalachiansValley threeprofilesshowthreedifferentinterpretations,butingeneral
andRidgeprovince(H.D.Rogers,1858);someoftheexposures hedepicted them as a sequence ofstrata dipping andyounging
that were most significant in deciphering that sequence will be westward,PrimitivebelowandTransitionabove,includingmore
visited on the last day of the excursion. The Rogers brothers thanoneunconformity. Inparticularhekeptchangingtheassign
quicklyrealized that the lower two-thirds oftheir sequencewas mentoftheschistsoftheTaconicRange,onthestatelinejustwest
thesameastheNew-YorkSystem,whereasthecoalmeasuresso ofWilliamstown, Mass. His pupiland colleagueEbenezerEm
important in those states lie entirely above it. Others, notably mons,whoasoneoftheNewYorkStategeologistswasthoroughly
JamesHall,showedthatthefossilsconfIrmedthesecorrelations. familiarwiththerocksoftheNew-YorkTransitionSystemwestof
InMassachusetts,theredsandstoneandassociatedsedimentsof theHudson,observedthatthelayeringandpartinginthebeltof
,theConnecticutValleybasindidturnouttobeSecondary;in1824 deformedrocks(wewouldnowcallmostofitcleavageorfoliation)
Eaton and Hitchcock called them the Old Red Sandstone, but dipswithfairuniformitytotheeast,andheconcludedthatthelocal
alreadyin1826Finch(1826) showedthattheyarethe NewRed rock sequence too must young to the east, but he clung to the
Sandstone of the English section, and that (correct) view was Eatonianideathatclassesorsystemsofrocksmustbeseparated
quicklyacceptedbyall. bysimpleunconformities. Hecouldnotconceivethat,ontheone
FarthereastinMassachusettsandadjacentRhodeIsland,the hand,thesedeformedrockswerecoevalwiththeflat-lyingstrata
question ofage was complicatedbythe existence ofcoalin the oftheNew-YorkTransitionSystemor,ontheother,thattheywere
Narragansett basin of Rhode Island and southeastern Mas coevalwiththehighlycrystalline"Primitive"rocksintheBerkshire
sachusetts(whichwasnotonthelineofthe1824profiles),andin HillsandGreenMountainstotheeast,andhethereforeproposed
the"Transitionrocks" ofWorcester (whichwere). Althoughthe (Emmons, 1842) to distinguish them from both as a newinter
associated"argillite"inbothareashadalltheearmarksofTransi mediatesystem,whichhenamedtheTaconic System,forthevery
tionrocks,the"CoalFormation"wasatthattimealmostbydefmi range whose·rocks had so confused Eaton, and which he now
tionconsideredthebaseoftheSecondary,andindeedEatonhad extended to include similarly deformed rocks in several other
lookedforitalongthecanalatthebaseofwhathecalledSecon regions. Yet Emmons always insisted that unconformities
daryinwesternNewYorkStateinassociationwithhis"M~llstone separatedhisnewsystemfromtheothers.Later(Emmons,1844),
Grit"(nowthebasalSilurianOneidaConglomerate). Hitchcock he accepted the hypothesis, suggested by Hitchcock, that the
inparticularvacillatedastowhetherthe(anthrar;ite Jfgraphitic sequenceintheTaconicregionwasentirelyinverted,butrejected
anthracite) coalinRhodeIslandandMassachusettswasTransi Rogers' hypothesis that tight (wewouldnowsayisoclinal) folds
tionorSecondary,andatonetime(Hitchcock,1833),becauseof and faults have scrambled the sequence (that hypothesis has
the grade ofthe argillite associatedwith each, decided that the turnedouttobethecorrectone),andherefusedtoadmitthatthe
NarragansettbasincoalwasyoungerthantheWorcestercoal,but present differences in the rocks maybe due not to originaldif
olderthantheanthracitecoalofPennsylvania. Aftervisitingboth ferences but onlyto later deformation and metamorphism (the
localitiesin1842,CharlesLyell(1797-1875),cameoutflatlyforthe conceptofmetamorphismwasjustarrivingfromtheOldWorld).
equivalenceofWorcesterwithNarragansettcoal(Lyel~1845,p. TheunconformityEmmons sawbetweenhis Taconicrocks and
196-198), and H. D. Rogers showed that anthracite and the"Primary"wascorrectandwasquicklyaccepted,buttheone
bituminouscoalinPennsylvaniaarecoeval;weknownowthatall hesawbetweentheTaconicandNew-YorkSystemsdidnotexist.
these coals are the same age, Upper Carboniferous or Pennsyl As fIrst shown conclusivelyby C. D. Walcott in 1888 (Walcott,
vanian. Hitchcock further equated the low-grade rocks ofthe 1888),itisamajorthrustfault orlineofthrustfaults. Emmons'
Boston basinwith those ofthe Narragansett basin and despite proposalofanewsystemledtothefamous"Taconiccontroversy",
Crosby's vigorous attack on this idea later in the 19th century whichlasted halfa centuryand isstillthe subject ofcontinuing
(Crosby, 1880),itbecamestandarddoctrine andwas onlyQues debate. Differingpoints ofviewconcerningit are expressedin
tioned,andthendisprovedbyfossils,inrecentdecadesofthe20th articlesinthisguidebookbyJohnsonandbyRodgers.
century. Thistripfollows"inthefootstepsofAmosEatonandEdward
TherestoftherocksinMassachusettsare"crystalline"(mainly Hitchcock," and is designed tovisit the areas mentioned above,
amphibolitegrade)andatfIrstwereconsideredsafely"Primitive" including ample time for discussion of the history involved in
(later"Archean"). Anomalousfossillocalitiesturnedup,however, interpretingwhat is nowclassicgeology. In this guidebook ap
laterinthe19thcenturyinNewHampshire(RogersandRogers, propriate historical reviews are interspersed with individual
1846; C. H. Hitchcock, 1871) and even in north-central Mas locality descriptions, arranged by topic and in the sequence in
sachusetts(EdwardHitchcock,1852),andattheendofthecen which they are to be visited. The daily trip schedule will be
tury B. K. Emerson (1898, 1917) concluded that most of the provided separately. The fIrst four days are in New England,
metamorphicrocksinMassachusettsarePaleozoic. Carefulmap startingintheBostonarea,proceedingtotheNarragansettBasin
pingbyMarlandBillings(e.g.,Billings,1937)andhisstudentsand and then the Connecticut River Valley, and fmally to the con
followersconfIrmedthisconclusion;almosttheonlyPrecambrian troversialTaconicregionattheborderofMassachuset~sandNew
rocks (theyarecertainlynotArcheaninthemodernsense) now York. ThefollowingfivedaysareinNewYorkState,tracingthe
recognizedinNewEnglandareMiddletoLateProterozoicrocks routeofEaton'sprofileandtheErieCanaltoBuffalo. OntheNew
along and near the Berkshire-Green Mountains axis (southern Yorklegparticularemphasisisplacedonsitesinvolvingsurviving
Vermont, western Massachusetts and Connecticut) and Late remnants ofthe Erie Canalthatwasfollowed byEaton and his
Proterozoicrocks underlying and surroundingthe Narragansett party. The fmal day and a halfis a transit ofPennsylvania and
and Boston basins (eastern Massachusetts and Rhode Island). Maryland, with brief looks at sites ofgeological and historical
Ironically,thebulkofthelow-grade"argillite"withintheBoston interest, en route to Washington, D.C. and the International
basinhasturnedouttobelatestPrecambrian;i.e.,.Vendian. GeologicalCongress.
Thebeltofhighlydeformedbut onlymildlymetamorphosed
rocksbetweentheHudsonRiverineasternNewYorkStateand
T169: 2
ME.
ONTARIO
Gulf Of
Maine
----+--
FIELOTRIPROUTE
• CITIES
o OVERNIGHTSTOPS
N
~ ORIGINAL COURSEOFERIECANAL
BOUNOARIESOFGEOLOGICAL
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o 50 100 150l<ll..OMETERS
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GEOLOGICALINDEXANDROUTEMAPFORIGCFIELDTRIPT169
Areas ofPrecambrianY rocks areshownbyhachures. The In the Piedmont and New England provinces, rocks of
rocks are igneous and metamorphic (amphibolite to granulite PaleozoicandPrecambrianZ agearemetamorphosedtovarying
facies, retrogressed locallyto greenschist facies); theyform the degrees,fromgreenschisttogranulitebutlargelyinamphibolite
CanadianShield,theAdirondackMountains,andalsoaseriesof facies. (Onthemap, PrecambrianZ rocks arenotdistinguished
thrustedanticlinoriafromtheGreenMountainstotheBlueRidge fromPaleozoic).
that separate little or not metamorphosed Paleozoic from Unconformable upon the deformed and metamorphosed
metamorphosedPaleozoicrocks. rocksareseveralbasinsofyoungersedimentarystrata:
In the Great Lakes and St. Lawrence Lowlands and in the -theBostonbasin-VendianandCambrian,deformedand
Appalachian Plateau Province, the Paleozoic strata are nearly mildlymetamorphosed;
horizontal, generally dipping gently away form the Adirondack -theNarragansettbasin-UpperCarboniferous(Pennsyl
MountainsandtheCanadianShield. vanian), stronglydeformedandrangingfrom anchimetamorphic
In the Valley and Ridge province, the same strata thicken tosillimanitegrade;
southeastwardandarestronglyfolded,withsomethrustfaultsbut -the Connecticut Valley, Newark, Gettysburg, and Cul
littleornometamorphism. peperbasins-UpperTriassicandLowerJurassic, dippingfairly
regularlytowardnormalboundaryfaults(eastsideofConnecticut
Valleybasin,northwestsideofotherbasins).
T169: 3
NEWENGLAND
MAPPINGBOSTON:ANINFORMALHISTORY
RichardS.Naylor
DepartmentofGeology,NortheasternUniversity,Boston,Massachusetts
Duringthe celebration ofthe United StatesBicentennial in todayforsomelocalities. Onthe1877map,heshowedtheBoston
1976,Bostonhostedthe68thAnnualMeetingoftheNewEngland BasinstrataasPrimordial,includingthefossiliferousWeymouth
IntercollegiateGeologicalConference. Articlesintheconference and Braintree Formations, now dated as Cambrian. Eventually
guidebook(Cameron,1976)suggestedagesofSiluro-Ordovician, (Crosby, 1900),he acceptedthe prevailingviewthat the Boston
UpperDevonian,orCarboniferousforthestratifiedrocksofthe BasinstrataareCarboniferous.
BostonBasin. Theconferenceorganizersconsideredputtingthe In1900,T.A.Jaggarcommencedanewmappingprojectinthe
questiontoavote,foratthattimealong-standingconsensusona Bostonarea,butafterafewyearshejoinedthefacultyatM.I.T.
Carboniferousageforthebasinstratawas clearlyunraveling. A TheU.S. GeologicalSurveythen assumedresponsibilityfor the
few years later (Bailey and Newman, 1978; Kaye and Zartman, work,andLawrenceLaForgedidmostofthemapping. Afteran
1980;Lenkandothers,1982),anewconsensusemergedthatdated excellentstart,thisprojectbegantosufferfrom delaysandcom
the basin strata as Late Precambrian. How could such things petitionfor funding. Its final publication as a U.S.G.S. Bulletin
happenatsolateadateinaninternationallyrespectedcenterof (LaForge, 1932) was undoubtedly later and briefer than the
geologicalteachingandresearch? project deserved. Prior to publication, LaForge's results were
Severalfactorscometomind. Stratigraphiccontinuityineast incorporatedintoB.K.Emerson's(1917)seminalwork,"Geology
ern Massachusetts is interrupted by plutons and by numerous ofMassachusettsandRhodeIsland."LaForgeisacknowledgedas
faults; the few fossiliferous beds can be tied onlyloosely to the the major source of field data for the greater Boston area on
other geologic units. Hundreds of geologists have visited or Emerson'smap.
workedin the Bostonarealongenoughto contributepapers on Inretrospect,acrucialerror(onEmer~on'sgenerallyexcellent
thelocalgeology. Theverybulkofthisliteratureisintimidating map)washisdecisiontocorrelatetheDedhamGranodioritewith
and may have inspired an unusual degree of deference to the theDevoniangranitesofcoastalMaine. Althoughnotstrictlyin
authoritieswhohavesupposedlymasteredit. Ofallthesepeople, accordwithLaForge'sinterpretationoflocalfieldrelations, this
onlyafewhaveattemptedtomaptheareacomprehensively. correlationmadegoodsenseonaregionalscale. Thestrataofthe
ThefirstmapoftheBostonareawaspreparedbyJamesF.and BostonBasinrestnonconformablyontheDedhamGranodiorite
SamualL. Dana (1818); their map was reproducedbyLaForge and,withthebasement dated as Devonian,it seemedeminently
(1932,Plate3,opp.p.26).Itdistinguishesgreywacke[sic],argillite, plausibletodatetheBasinstrataasCarboniferousbycorrelation
amygdaloid,fourtypesofmassiverocksthatwouldnowbeclassed withneighboring,welldatedbasins,althoughtheweaknessofany
as igneous rocks (plutonic or volcanic), and alluvion. The directevidenceforthisassignmentwasopenlyacknowledged.
greywacke, argillite, andamygdaloidcorrespondquitecloselyto Inthe1920's,M.P.BillingsofHarvardUniversitybeganlocal
the Roxbury Conglomerate, Cambridge Argillite, and Brighton mapping, and he went on to become the doyen ofBoston-area
Melaphyreasrecognizedtoday. WhenEdwardHitchcock(1833, geology. Inadditiontosurfacework,hesupervisedthemapping
1841) surveyed the geology of Massachusetts as a whole, he ofbedrock tunnels and attempted to develop a comprehensive
dependedlargelyontheDanas'mappingaroundBoston,buthe modelforthelocalgeologyconsistentwithbothstratigraphicand
specificallyidentifiedthegraywacketherewiththegraywackeof structural data. Billings (1929) soon reassigned the Dedham
the Narragansett Basin ofRhode Island and southeasternMas Granodiorite to the Late Precambrian, the age that is accepted
sachusetts, including its Norfolk County (Mass.) outlier, which today, buthe continuedto date the BostonBasinstrataas Car
comeswithin5kmofthesouthedgeoftheBostonBasin. Thus boniferous. Heneverdiscussedthepointthathisreassignmentof
theidea ofcorrelatingthe BostonandNarragansettbasinsgoes theageoftheDedhamGranodioriteliterallyundercutmostofthe
backatleasttoHitchcock. basisfor datingthebasinstrata. By1979,however, Billingshad
W.o.Crosby(1880)publishedaGeologicalMapofEastern cometoacceptanolderage,andonamappublishedthreeyears
MassachusettsandofBostonandvicinity. Thismap,anoutgrowth later,in1982,heshowedtheBostonBasinstrataasPrecambrian.
ofthefirstgeologythesissubmittedtotheMassac~usettsInstitute In a doctoral dissertation submitted to M. I. T., K. G. Bell
ofTechnologyisthefirsttoshowfamiliaroutlinesformanyofthe (1948)preparedamapoftheGeologyoftheBostonMetropolitan
unitswerecognizetoday. Crosbywasstronglyinfluencedbythe Area, but this map was never formally published. C. A. Kaye
Neptunistleaningsofhismentor,T.SterryHunt,andapparently (1980) subsequently remapped much of the bedrock geology
henevercametotrustthe"new-fangled"petrographicmicroscope. around Boston, with special attention to the coastline and the
Todayit canbedifficult to decipherhis nomenclature androck harbor islands. Billings (1982) disagreedwith some significant
descriptions, especially in the case ofigneous rocks. After his featuresofKaye'smapandofKayeandZartman'sinterpretation
energetic start on a long-term mapping project, his attention (1980).AlthoughKaye'sprimaryprofessionalresponsibilitieslay
turnedincreasinglytothenewdisciplineofengineeringgeology, inthefieldsofengineeringandsurficialgeology,hespearheaded
and his field results were never fully published. Despite these the effort that showed that the strata of the Boston Basin are
problems,Crosby'spublisheddescriptions arethebestavailable Precambrian.
T169: 4
ERRATA
Contemporary work is directed towards understanding the this work were presented in a symposium on the Boston Basin
complex facies relationships ofthe basin strata and developing Adjacent AvalonTerrane ofSoutheastern NewEngland (Socci
models ofthe environments in which they and the neighboring andothers,1987)andaretobepublishedinaSpecialPaperofthe
volcanicandplutonicrockswereemplaced.Papersrepresenting GeologicalSocietyofAmerica.
FIELDTRIPSTOPSINBOSTONAREAANDVICINIlY
STOP1. SQUANTUM"TILLITE"
(BOSTONSOUTHQUADRANGLE,MASS.)
71°02130"
r
if' ··Thlmble
"".lSland ----.
I
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Halftide'Rock"--- ·:w:
.
•
,'"
i j
QUINCY
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l:1==============:::::::31
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FIGURE1TopographicmapofSquantumandvicinity(fromBostonSouthquadrangle).
The curious conglomerate or diamictite ofSquantum Head 1) Crosby (1880) held that they are Cambrian and probably
(alsocalledSquawHeadorChapelRocks),inthetownofQuincy marine,becauseofwellknown Cambrianfossil localitiesjustto
onthesouthshoreofBostonBay,hasbeenknownformorethan thesouthinrathersimilarrocks,thoughthefossilsareknownonly
acentury. Itisanintegralpartofthestratigraphicsectionofthe inlargeisolatedpendantsintheintrusiveQuincyGranite.
BostonBayGroup,showninFigure3(Billings,1976,Fig.4,p.8). 2)Shaler(1899)heldthattheyareCarboniferousandprobably
Duringthelater19thcentury,twohypothesesfortheageand fluviatile andlacustrine,becauseoftheirsimilarity(firstpointed
originoftheBostonBaystratacompeted: outbyHitchcock)tosedimentsinthenearbyNorfolkCountyand
T169: 5
TOWER tv
a I
FILL
1=-'=--1 I
CAMBRIDGE
- - FORMATION
I
I~ ~ISQUANTUM ~ ~ ~ ~~ / ~
~ MEMBER ~~ ~ ~ / ~~~
I·::~:~·:rl ~
....... DMOREMCHBEESRTER ~ I~~
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PARK
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FIGURE2GeologicmapofSquawHead,Squantum(fromBailey,1987,Fig.4,p.211).
Narragansettbasins,whosestratacontainwelldatedfossilplants, thereafter,theSquantum"tillite"wasconsideredaunique North
and because of supposed tree trunks in the Boston Bay strata AmericanrepresentativeofthePermo-Carboniferoustilliteofthe
themselves. Gondwanacontinents. Oneperceptivegeologistfromelsewhere
Bytheendofthecentury,theCarboniferous,lacustrinetheory whojoined an excursion to Squantum Head during this period
wasfairlywellaccepted, evenbyCrosby.A glacialoriginfor the reportedthathalfthegeologistsontheexcursionagreeditwasa
conglomerates around Boston was first adumbrated by Dodge tillite because it was Permo-Carboniferous, and the other half
(1875,p.408-409) andwasworkedoutindetailbySayles(1914), agreeditwasPermo-Carboniferousbecauseitwasatillite.
whofoundhisbestevidenceattheSquantumlocality. Fordecades More recently both these conclusions about the Squantum
South
North
I...,h...
5 "'I!
A B Of
4
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3
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2 • • • • • • • • • • • •
o 0 0 0 0 0
,"
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I '\ \,/J/"/ " /'
Complex
J~s
o 1<XXJ
Meters
A
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LinesofControl
FIGURE3StratigraphicsectionofBostonBayGroup(fromBillings,1976,Fig.4,p.8). Circlesrepresentconglomerate
units,triangles-basalt,dashes-mixedargilliteandsandstone,blank-argillite. TheBrookline,Dorchester,andSqauntum
MembersmakeuptheRoxburyConglomerateformation. Thecapitallettersindicatemeasuredstratigraphicsectionsonthe
surfaceorintunnels. Verticalscaleonleftisstratigraphicpositionrelativetobed"zero"(oldestunitnorthendofCityTun
nelExtension),inthousandsofmeters.
T169: 6