Sen eee - ay pa a a ate ms w cate ia Uideters nee Sno eae DEPARTMENT OF THE INTERIOR MONOGRAPHS Or THE UNITED STATES GEOLOGICAL SURVEY WASHINGTON GOVERNMENT PRINTING OFFICE 1899 UNITED STATES GEOLOGICAL SURVEY CHARLES D. WALCOTT, DIRECTOR Ga O10: G Ne OF THE NARRAGANSETT BASIN BY N. 8. SHALER, J. B. WOODWORTH, Anp A. IF. FOERSTE Wie AUS HTN) GOAN GOVERNMENT PRINTING OFFICE 1899 CONT EN Ts: TUG Oi teh ap aN ee Le Re ee San ee ete eel eo Sage een oep oS oDpOCULooeud Ea nod ooo ees » IDOE OS ae eR Soe s boot SEP AOa OOS So Boge SSS aon eEH DRS on SE Lee Neeae Ben bpinStcce coboehaceaco cosabEes Part I.—GENERAL GEOLOGY OF THE NARRAGANSETT BASIN, BY N. 8. SHALER. Chapter I.—Position and surface relations of the Narragansett Basin, and the rocks it contains. Gemennl WeAED sse5 cobsacigeda pHodsa eabawseeua coos ccodoo boon sone doen ED Sede deccouosSoa0 4o0r Straticraphicalvand:orogenic relations << i- 22 2-9-2 = eee ie = ie ie wom ele nee TRS WUT Ole UNE AOUON. OL CHROMO aOR S545 ceoone sone.Gudd soo boop Gono nosdb soos 66ee c5G0 Sens ONCRWMNWSG EMO WNGMNA) Sac5 oeaeons cons coda seo GacO casa soude0 Geos sepcus sass asS0qce0 veqdar IDES MOIS Gre Wine) NESTON Sees Cons ebb a cone Boabes bode onuS cbonus goaS UoeSebbodoEs ScoG seo Sere Chapter II.—Physical history of the basin-.---.---------------+--+- 200+ 22-252 222222 2 one Relation to marine and atmospheric erosion and deposition........-..---.---.-----.------- Ageof Carboniferous rocks of the basin --.--------.---. +--+ +--+ +2 -2- -2 22 22-222 see eee Original relation of the Narragansett Basin to the sea...-.---.---.---..----.------++------- Original distribution of the east Appalachian coal field .....--.-+---.---.---.---++--------- ATIoIGIT min OF UNG HEINE .58 Heb00s0c00 soda saad Adar coupes ese56ano05 5680 9acm a7 poc0 sconce Relative erosion of east and west Appalachians -....-....--------------------+-----s02---- TROGA CAS ORIGVAL oocdss osecde S055 cond cogccaccos GodkaS Hacs coSaeoES RAD aaoseIndeSs desece General statement concerning base-leveling .-.......-..-.--------------------------------- Chale OF enOSHIOM 66555566 cond apon bee obo0 dino SH oone Dodon eqes ssoson coneoobussdopocoua ABRORS Ch TOSUS' Or UNS WHR 655550 deqconoseubsoU60 Good bode eese oobdes sosads cece ceeu ccodae RGA MOM Ort pa HO CHOGOM 65 coodc0\4o00 sadcop soso SeUbe5 bobs aoUb saad cesoob ses soogee Recordivalucroticonelome nates eerecte atest taal alas lel maps ala) al le pel elie otal ime) miele demlayal et elelot= Red color of the Cambrian and the Carboniferous. ......-.-..--------- us eae eya nea setae Chapter III.—Glacial history of the Narragansett Basin.......--....---.-----------+-+++++---- Chiriomubinanis COmmlonn rs 5656 64660006 bebe BeaDoe codeod Saceen SHag sede bs0ca0eda0 puoe soos IAN Glla@ienl jrAMOdls 265 b505 sa66 S046 pada 65050 beea nobE dong coe h660 coScas ceGoses5 HascosbEse ANTTOUIMY Ot CHROMO c5co0 sono cacao aseSdooq05 cece Suagao cade Song H6e0'0058 S500 Ses Soon Sesp cabuRS Chapter 1V.—Economic resources of the basin .----.--.----.------------+------------++-------- Soll) = so555 casa dsecbe 6a6d S645 0500 05016008 sece bes Gude SoSd cG0N BbeS coud ose See aca SoeE sonene GORI) cc65 dosd'cdae Sede o660 cued cone A6ob cc0Sc0 Docquy doom sdb o oneS bpodao Dono SasmdescoubpEDeose Canalo OF Whe AWS Seoh eden Sed6b6 cage sasnasud Bead soul ponedd ddan cosane sseodegy Uaud OE Ciramicranignics Gr Whe, COM. co2d46 so06 655059 sadeas coudbogdoguS ooSdsu pEeeasossocesSnece Conditionsloefutureveconomichnonlae=seeeseeeen semana se ee aeeeee casas sees ee loom OxesS Ligon TOUT GlepOsMts coco Beecoo nosed SonaoS HSDq0U HUCUSU e=ouEE DnoSe>o HeEeEs cooecoedaS Part II.—GrOLOGY OF THE NORTHERN AND EASTERN PORTIONS OF THE NARRAGANSETY® BASIN, By J. B. WooDWORTH. Chapter 1.—The problem of stratigraphic succession -...---.---..----.--------+-----+--++------ Repetition of lithological characters........-.....-.-------------------------.---- Mranstionvofelibholooicaltcharacters|ese< o-\\a6 <= a\--" «nie el eee eee eeisce Bffecte ofr ome OUstingrusions set see eet: ye jocte ak asiatsiae ciate a ene ere ete ete Metamorphismeesee seen se ene: Bora caus oqodogage loos ppog oadaas secidog cscs deoene IDOHGhunyer Eyal MeL HPMAYS so65 conn pasa boodeo sadeue sean isuad conconcs J39Seu cucu decd acudeE IDSA HON Sad Sho5 sob dooke Hoodoo aceo cece soe ehdonacdd core boseoG S600 Gace cuceeods . oe oo 1 OF eo 0 0 to bt aS or =) IAIN onde A oom S oO wm UW bo io) VI CONTENTS. Part IJ—Continued. Chapter I.—The problem of stratigraphic succession—Continued. (ClEXCEN TO) Noe aosooecn Sano SES eee > anes s5G505 6600 coo0 Feamimaoo S605 6555 0504 bapcaDrS bons Submergence-.-..---.--.--. -.--- Aihsencerofuantiticral (excaivait O08) ete eta eee eee ei eee ee eaata Chapter IJ.—The pre-Carboniferous rocks.-.--...-------------------------+------------------- Algonkian period ....-..----------- +----- +++ 22+ ++ = 22+ +222 eee nen en ee eee ee IBM WONG) EEMNOS sscoa5 aooseo casse0 senoDe SoSo5s Doo sua voodce coeCnoesSpSs soESoeseSco nas Cumberland quartzites ------.- SE EAROO SAO e sos nS SESS An SSA oaa CAS EAE SonseRaopabes bsca AN Maia OMNIS coc coedes poSooS dee ssebos sscond Sone on odbEs He sanuSoone seosso pesese Shoal ouNVGl Mb ONS sos5o.c6 sea cso0 cede Sse ose eos OSeSae see oou cocce oeasoocedees (Ohne opera PEWIOG) cans Saes cos cone ce Sees Coos bse code boom bane esos ces Heme eeco ese se secs eons Jeo ee CEN RMN — oon seen don cos Sono seeeoc SSNS Sos6 Sone noes Seue soos Soom e Sede cesses Middle Cambrian (unrepresented) .--.---------. --.----- =.) - = ra ee eee ta ea EIN OnE Whayaere Capea ib Gobo 6 kou cs coos cops esos Seve usae Sugd soso cod dene dosd Seuc scgu eens oeoces SH him eHA, jarmordl (HhaMGyNTAeIMIG MM) os ode boos eobe ba55 ssocee Gene obese caso gas oses Goad eaoosces (Clnerth oS NHIES 52 bob ches. cses ede Sasa saddogda aeasbosn secoadosecas mood cuca deseo bees Chapter III.—The igneous rocks of the border of the basin....-.....-.--------------------+--- Graniticirocks ese -e nee aaa eee cee nee ee niet eee eee eee ries cere eee asrettetasers TDI Arai IGM) Sos Sbo6 sos5q5 os00 toes sod sade Sans Gadd 5635 5c00 Hod bos S00 dSa5 cade Granite-porphy types eee ee eee eee eee eee eee een eee eee eee errs OLIN re Go Ao As Goo odng coon asedas soades docs Gobs dnaoue Setbedoassae dseckoon s5K0 (Cedars lovibleyon? Sonam: <6 c6bedo sues sacs cabslsoes cass coee obese soso Hoes soos ascnsce Chapter IV.—The Carboniferous basin........--.----------------- ---- +--+ -------------------- Generalistnucturejoferheubasine sess cesses eesee seen eee eee ieee aan ieee erie Maps of the boundary of the basin....-...-.-.-.--.-..---2-.-.------------..----- Boundary of the basin on the north and east...-....-.------.-----------+--------- From Cranston to the Blackstone River.........-.....--..----.-.--------- From Blackstone River to Sheldonville .....-......-...---.--.------.----- Connection between the Narragansett and Norfolk County basins.......-. Sheldomvyillleycrossptaul teers eeeise eee eters ase eee eee tiecse seer Hhromysheldonyalllesto:Hoolish#enl essa e ee eae eee eae eee ene PoolishebHillgfawltwess-eeteeeeee ee eesee eee een ee eee eee eee eee aeae romyHoolishyEillstoybrock:toneees eee seee es eeee eee eee eee eee eee eee Nha bT:) a TAbPee name ry Cea eA RUD IE ean en en es Oe booidane deccie Dance ObOO SaSe.OFOD Nemasket) granititeaneaiess sess eee me eee eae alae ise eater eters siaet= SWHATNEIAY So Soa incoconasadshos sedqce Soobss Soagds HeCUss Sosa sascco eSbass Cosa DSas Se08 Chapter V.—The! Carboniferous strata ~~ 522-2 -(92 = = Semin een on sn oe eee ee eine winavi Determination of horizonsiwithin' the basin’ 2-2 =). .- o-- eerie eae alee se een onleee aa Meansiorndeterminine;superposivlonte pes eeeeee eee eee eee eee eee eee eaee sae ser ease Tabular view of the strata in the Narragansett Basin.-........-...----...--..----.---.---- Formations) below, the Coal Measures) == 2 =o. oo = i - a n nie eine meen nia enlace meee oe see OMB KANN GROW sosscdoanooe oso ose0 BGe0 6008 S900 S000 Bote doDS ease sadaneoS cooN Beno SocOSs IBESFl AKON INEGI Goss coco ades cosese geadob edqSca nos0 SpeSEE Seon SaGKos d50550 Cons SOUS North Attleboro exposures ---~ 5. - 2-2 oe ee nn ne oe wn ene Pierces Pasture in Pondville, Norfolk County Basin Absence of basal granitic conglomerates ....~.-.-......-..---.--.--------- Geographical conditions indicated by the basal arkose Absence of iron oxides in the basal arkose.-..-....-..-..--. -------------- Absence of carbonaceous matter along northern margin ..-.....------.---- 1D yO (OMY Eel MO) ADIGE) pooods Esco soncos cosa hob sae SHesSeoteeee Henn soos eaooeS CONTENTS. VII Parr II]—Continued. Chapter V.—The Carboniferous strata—Continued. Formations below the Coal Measures—Continued. Pondville group—Continued. Page. Suprabasal conglomerates .-.-..---------- ee eee ee eee cece ee cre rere eee ee eee eee 140 Millers River conglomerate ....-..-------------------+-----+ +++ 2-- 222 --- 140 South Attleboro exposure. ..---.------ ---------+ -- +--+ eee ee eee eee eee 140 Jenks Park exposure in Pawtucket...-.-..----.----------+----------------- 141 Wamsutita group -.--.---------- ---- 2-202 -00 2 eons ene enna tenn rn ne rrr eee 141 1elateele BiB secead seco WocoLeSeneae LooaoebecrcoocUsiesoeneScomceano” bacocscersad 142 Area along the northern border -----.--------------+-----+++++++ 22-222 222-07 143 Gray sandstones of the northern border..-----.--------------------------- 144 NON MAIO) EN) ooobecccouSe coors coor enolos SSewos anos soose sou pesemessoeos 145 Conglomerates .....--------0------- +++ +25 ---- see eer rere ree eee 146 Ghali sae occ otec eoe eae Pac acouoes acon sducerbeacde Succ cased cedceectoc 147 Nese Geesae cocues SeoS Sade ceas eHdeoe cos Usobeome sosoareeessSdoscsecr sacs 147 Clermpeny LI DAS eee Cees Goeene seccesceeocu aose deeds sdcmuoasss sasacccebecscsccas 147 TEN el ERRCH) Aa sed GeooaSs GeseEe Geeecs saboeedese crocs GercecmcHs Soca poouiecdc 148 Red beds in Attleboro, Rehoboth, and Norton ..---.-.-.-------------------+------ 148 Norfolk County area....-..---------0------ 2 eee ne een nee ene sees 148 South Attleboro limestone bed ...-.....-...----------+ ------ ----2+ +2222 eee 149 Attleboro sandstone .-...---.----------+ +--+ +--+ 22-2 eee rte 151 Igneous associates of the Wamsutta group...--------------------------------- 152 IDRAIDAE) eooeese chad soc ode edabece oobc58 Gece cosesacdassoeo59 Oeeccs caachcHe 152 Quartz-porphyry group-.-..----.--------------- +--+ 2222 e222 renee tree 152 Diamond Hill quartz mass .-..---.------------ -----+ +--+ 20 reer ee eee e eee 155 Wamsutta volcanoes ..---..------ +--+ 22 ee ee 2 ee nee ee re eter e eee 155 Folding of the Wamsutta group -.-------------+----+ +++ +222 2222-22 r errs 156 Flora of the Wamsutta group .-...---.---------------- +--+ ----+- +222 +--+ 158 (Ci AILAN ASIUNEE. < Scooeuos na06 Hood SHG boSEcd S666 S005 2009 ECR EEO ES ARE OOS5 GODOCG O8c0 CHC ooGBG0e 159 (Ghomyion W0eeseg aood coos cou boo eee sac SOU eaed 6o- S50. S8 5600 085003 OCR SOCODSSSE OSG COo0 159 Providence area .--..--------- ---- 2 ee ne ne re Ssoscsesbe 159 Pawtucket shales ....-.-.-------- eee eee nee enn ne er re rere 162 Sockanosset sandstones. ..---.------------------------ saobeb OsbeeoEoEe ba65 163 East Side area in Providence ..--.-.---.---------- ---- +2 2-22 cert rere creer 163 Tenmile River beds. ....-------- ---- --09 <2 05 oon nnn nn ne een rrree 164 Lebanon Mills exposure .-..------------ +--+ +--+ ee rer rere rere 164 East Providence area....--...---- 220 --- = 25 2 rn et ne 164 Leonards Corner quarries. --....----------------+---+ +272 crete r cre rrtr ree 165 Section from Watchemocket Cove to Riverside ..--.....------------------- 165 Halsey Farm section at Silver Spring .----. ------+--+-----+ +--+ 00072 007- 166 Exposures in Seekonk ..--..------ +--+ ----20 seee cer ees reece tnt 168 Hunts Mills section. ...... ---- ---- --+--- +--+ 22 - eee rr ene eens 169 TEGVEHING EHMIOENO ssSeb5 58655065 b2Ss ddasco bSoses SaaadS Sond cose aeebeeCeedan osouesosaousece occa 284 Tee Che HOMO WOO < 5 55 h5 bso5 ssa esbano cosebes ose ao soHs couScE sobbasisSoaen sacs 286 Eastern shore of Aquidneck Island as far south as the second cove northwest of Black IRON 35-5 ooSh So Secodb boosco Bee sed oeo5ed Seceoa SebUdS Sse coesnassoseeceadsaduse Socdocooee 288 Coarse conglomerates and underlying sandstone series from Black Point to the north end Ost Simvii ys) JBVEAKON: S545 S55 coc dad once bdc9 back bacdes Sooo Bobousco cece Dogo cedcice Sos adodono 290 Coarse conglomerates and underlying rocks on the neck at Eastons Point.-..---.----.----- 294 Paradise coarse conglomerates een. s= =m (allan a wn sie ellen nim wale ieleie =~ ole mmm = mnie lala 295 IPE REAGHIES) TROCRGa5 os co onbd dbdeco beans Pood cas Sood SabEe OuGS Sat ooeS Cabos DaSedada sessee 295 TUNG) Je nvenns IROWRS 2 oa5 565.5556 cose ceca bacsas Scan SHESa0 BoESes Seaooe Hoosen Deacsencodcsscae 298 IDREH Ch OMNI OUS HE) S55 o566s5 esosccus acdsos onaans Eade pec Sooune + Seeseancosse s5a5nc0 Boe 300 Isolated conglomerate exposures near Eastons Pond and northward. -...-.--.------.-.----. 303 Miantonomy Hill and Coasters Harbor Island conglomerates .....----.---.-------.-------- 304 Niemi@n@uiny 1e0Il o-oo Sea caso encs Suce bdooed coe sous seeps rods cscs HedoSo.nc0ss SeSccooE 304 TBeA@OM, NN a5 sow eton ceeded case séad sooSsd ease eooSoUeCOSSE sag Seda sbSSRSeassed Gaaues 304 Field exposures of coarse conglomerates... -.---.-.-.-------------------------------- 304 @oddineton Neck oo. oon aoe a) an ane oni s oie ene wes ee coe nim mene ees on nin 305 IBEGTNOD JRO sac5 code bs onecdodesd asacsasessodseadao cs daaddotonosdes soucdonecdsEecosnss. Clk) Coasions Tlrbor libel bseoccodcacddead se conn Hees cesd Cond beodad Babes aE Papa RoEeEoobenis Olle New porta blanboris) ands tree se cjeee am lamina am amare tele ele eam lenin almnin = 307 (Gill Roya oo ses5 cdoséo Seisece 6 boso boon coo ons coODSE Sees Gon ae sciss Sb0ne— boeets Seon Scoads 307 TROD UIE ss Boo sas Edad Sobbe9 SSS SEs SoDObN S00 DOCUOS EUEUBObEEd SoScS ban Gcadeascoe 308 Comenn@ren ISEMGl-b5 S53 505 edsaos cocasd sosnS ces eGo BOSON DOS OEINEGGEN coSoScsHosa0C00u0s5 308 Line of separation between Carboniferous and pre-Carboniferous rocks.....----...---- 308 GoatelslandvandubhiptleplnmeyROc kee cers sania = ama) lenisl ia = ala alma) meatal ee ae ella aa ar 309 Mba CRG Gs eno booeco Ce eeee Secoos Caeess seSeee Co eaeO nec oes Saeo eeeads masioeosas6 Soccer 309 Morton barksandusoubliwace aera ates = aimee folate terror alae ieee Aa eaediee 309 Northeast lines of possible faulting. --- ~~ ----- - eee en en eee wen 310 Carboniferous rocks along the Newport Cliffs .......-..-------------+----- +--+ +----+ +--+: 310 xX CONTENTS. Par? II]I—Continued. Chapter VI.—Aquidneck, or the Island of Rhode Island, ete.—Continued. Newport Neck ‘and southern’ cliff rocks: =. == eee ne ee oan cinerea eee eseleie Greenish igneous rock in the cliffs southwest of Sheep Point .....--...-..--22 22.22... Granitearealatithersouth endiotitheclifiseess-cenceee ee eercce eee eee Gee eee eee ae Graniteyares) onjeastern Newport Neck: : once. scleisce eee eeeeees eee ee see ee eee reer Greenish and purplish argillitic rock of middle Newport Neck...--....---.-...-.-..... Pre-Carboniferous green and purple shales of western Newport Neck ..........-......- Shale series from Coddington Cove to Lawtons Valley. .-...-...... 2-2. 22-00-02. ween ene Greenish-blue shales of Slate Hill and southward .......--. ....-.2------- 22-222 eee eee eee Shalevseries northiof Mawtonsavalleyeece sac eeiee eae ee el - eee renee eerie eee eee eae Shore exposures north of Coggeshall Point:.....---. 22.20. 0222 2228 ene ene cee we ne Portsmouth minejandmortheast wand -ccacees=eereeesaeeaisee tee esse ee reer eee eens Line of exposures three-eighths of a mile west of the Newport road-..............- 2... Shalejseriesiates atts bial lege ese tere ares ere ete eter catee ens ree eye tater a Green shales and conglomerates of the northern syncline.....-..--..--.-.....-..----.----- Green shales along the western Newport road -.........-.. 22-22. 222.2202 eee eee eee (Cone ONES Soss55 facade cdoada Jdabecd dood soodmagson sdeH oodEbO q6e Soo once Sooobe seems Relations) toyolatepkdallish'al sieeve tee meme eer sinsteaee tele pelelalepe eter tae ete ee rae eee eae Chapters Vill. They ine stowmisenlesseermcsscree cee rane ne rse nee Pe eeeee seer eee eee reese Unity and lithological character of the Kingstown sandstone series. .....-......... Section/from) the Bonnetitoy Boston Neck: 22 ees cmeee ee eaeiaain cee eeieeeeleneeee ee Section from the Bonnet to Hazard’s quarry and Indian Corner .................-.. Kingstown series in southwestern Cranston and western Warwick.........-....... Probable thickness of the Kingstown sandstone series in Cranston and Warwick .-- Wanwick Necltexposuresserseresere Hae r erase eee S ee eee eerie eee eeeeeee Exposures on the western islands of the bay ...-..-....--.2.---2 22-220 eee eee eee Thickness of strata between the Bonnet and Dutch Island ....-..-.-..-..........-- Lithology of the Dutch Island series ..-....-....-- 2-2. 2200 120 ee cece eee eee sees Beayersileadssectloneseesacaceeeneecie sm eeeie cae ee eee Reece eee eee eee Total thickness of the Kingstown series, including the conglomerate at Beaver 1 SEN Le eS 8 Bo DOCNeT KOE AS ESE RSET an eee eS eROOSe mem isbn peas Se580 Wiesternishorejoty Conanicutieecemeereneer ee serrrtecse-tieee eee ee Eee ee eee eee Hasternmyshoreyofa Conan cnitmeenaeee see meases eerie eee eee eee eee Eee eee cere Probable folding in the northern part of Conanicut Island...............---.--..-- LEO IEG ooh ose obo scoods seubed coodue pabesh bdoabO Gand HSAs Seboen Seba sesese BuO Kingstown series exposures on the western islands. .........-...-..-222------+----- TERME NGS) IISMEN MIL 5 S5o0 Goodos oddo rao cE daae cand Beno noNO pads baDd USES SodoobHOO gabe WV Gisuarnt, HES O INGO Sosa ds66 Sood copa sedeo6 do6e bdob soon dooce cee Géiscoo cosbeseaaS INUIT MSHS INGYelisgs BSS olbsoopo caso aosoDeg badelosou sobd bobs dseolcose osacebSabod bdandenS Kingstown sandstones equivalent to lower part of Coal Measures group..........-.- Triangular area of the Kingstown series in the Narragansett Basin, narrowing EO a Ki eso e Shc pots Goo Scy cSes Sobodo SO OOU SoUb LS ED baad OooaRo boEcoo OuSe SUud Thickness of the series and evidence of folding -....-..-.--- 2222222225. eee ee nae Rocky Point conglomerate and its connection with the estimate of the thickness of the monthernysecloneee-ee rere eet eee eee eee eee eee eee ee eee eee m Chief features of the Kingstown Series .--- 022... 2. 02.22 eee eee ween wn eee aS Hossil-planiijo callities seeerte petal ate rela ested teteiale lobed sterel=toteieletarsteyelaiee ete rete tee Chapter Vill —MheAgquidnecksshalesesesmece essere asoceeceieresiseiseieeesisencieeeeeeerecee renee Area occupied by the Aquidneck shale series -..- 2. 6. eo cee eee e nee ons wee eee wens SoutherntC@onantcuteeescaeeees-meeeeeeeteeeececcciiseisaeciestee ese see eee eee eer eee eae Prudenceplsland Sees emeresntsess ee eer ee ete sites coer telecast eee eee tee reer Thickness of shale series on each side of the Prudence Island syncline...........-. Bristol! Neck) ios saseweseseenicieeiscesee eee see sclericciesec cnet eee ee Seen ee eee eeeee Aquidneck Island. o.3 7scjlso eae as oa caiienoel see oe ae a et ee ies aoe Se EERE neee Thickness of the shale section east of the Portsmouth syncline ............... Reieniceciets 208 CONTENTS. Part I]I—Continued. Chapter VIII.—The Aquidneek shales—Continned. Probable thickness of the shale section west of the Portsmouth syncline ..............-... Hitholovicalévariationsinjthershaleyseriesesr sesame ea eee sae a ele season Geological structure of the middle third of Aquidneck Island ........--.-2--.---.-.--. SAREE DKON KRG GL s SiseoeSacoubesod. code as booSe she cGRon QSenLAao Uae DoD eOneN ee BeaEree GonldsislandiofathopMiddlesPassarepennsren tees tesla ee etaaee eee cctecee oe eaeeee SoutherntthindsofeAquidnechkwlsland ees eye sine = cites = <)ereeraiee eae Seen see nent ee Wppewencentshal esiohiihepA quidnecksseni ese -smpsse eees seta eee eee epee tee one Sakonnet sandstones of the Aquidneck series west of the river .............--. 22-2 -2..---- Mhicknesslorpunep per Sreencsnal esi e srr meer apart yee sree eee nee amon era phicknessofneoMconnetisands Ones) ee emcees acne eee see aes ee eee eee eee NorthermextensionsonauherAquidneckishales). cass.--e sees ene eee ate eee eee ee eee ee Equivalents of the Kingstown sandstone and Aquidneck shale series northeast of Warren Absence of the shale series beneath the coarse conglomerates east of the Sakonnet River. -- Wedge-shaped areal distribution of the Aquidneck shale series........--.........--2-.---- Equivalence of the Kingstown sandstones and the Aquidneck shales ..............-.-.---- WOSSi/S;OnscherAquidneckpshdlecsenless secret cme ae nen eee ne see eee ee ee eee Chapter lx. —heseure abonyaconolomeratesa- asi sss sinine ieee eae eee ce Serer eee neee Coarse conglomerate overlying the Aquidneck shale series.-...............-...---. Sakonnet sandstones within the Aquidneck shales, in transition to the coarse con- PUOMNEIEIG = séaceo sbo6 dons coos neo asco caged Sobuen Hoda done seadoseouSo Souauosoenee Coarse conglomerate forming the latest Carboniferous rocks in the southern part of hemNarra canseuupb as ieee ee ame ae oir =e cee sein ae ee ee eee Pureatory.conglomerate as a typical exposure. ----.----.---= cose. 22s eee eee ce ee Identity of the Purgatory and the Sakonnet River western shore coarse conglom- QHRUD scooter acess osbe0 Gadd aosdds SESS oScaSUSSSoEEbaSAsa oooseC sockto onde Stee nses Possible syncline between the two western Paradise ridges of conglomerate Hanging Rock ridge, possibly the eastern side of an anticlinal fold ......-......2.. Dips immediately east of Hanging Rock ridge .......--..--.--.--. 2-2-2222 -----e INTRETF OREO OCONEE sac sce Saas asocae eseda cous MedeeEseseuc ROUnas cdeceteces Sooesc Southward pitch of the great Paradise-Hanging Rock syncline .................-- Southward pitch of the Sakonnet River syncline........-...--2-..-...2..---.------ Wiestermcoarse;conclomerate exposures scene sossi)4- sean sel ae as seen eee See eee eee eee Possible syncline immediately west of Miantonomy Hill .................22222.2.-. Possibility of two horizons of conglomerate at Miantonomy Hill ................-- LESAN EXTON Ee Nea soo Bocdas Heenenos cdddindee Sesecooos bond accese scad eeeaae Geological position of the Newport Cliff section .........-....---.-2--.22.--+----- Poxtsmonthisynclinalconclomerate miasee ce aes) oe aac ocieseeioee ee oscee = ace Conglomerates of Warwick Neck and Swansea.........-....---.------------------ Thickness of the coarse conglomerate. ......-...-.-.-------------e-- Boeese ocd Sear HOSSUIMO CATES Weenie ete meree eerie a nyt ere ad GS bdou enoSosbS Cob bRe HAS CooaEOoE Chapter X.—The arkoses and basal conglomerates ............ 2-2-2. 222-22 2222 nee ene one eee INEIIIOLS GNSOSO sasese cece loc Se See sed Hose sede SaeeSalbadebeisess Hab Sac cations dcodaoSEsetodses Probable relations between the various granites and pegmatites and the Carbon- TLELOUSH DEUS ester alec tar se ale eicre cise lel Neeser aia Ieee Me ES eae nate AUB ORO Biel ROS) S505 Cosco datots caso Soe Baa LOO SCO SEC BoC MEE ane REO SEeoceHoFolpeuboucHootaSons Brom (Steep Brooksto;yNannaquacket bon decease a2 ase oe) assent saison ee eee SouthioigNannaquacke tion dae cesse sania kee eee ee sess see eee nee eee Equivalence of the Tiverton arkoses to those near Natick......-...-..........-..- SEO GE EOS) ceo Soccdoces ceagecobbee ced acsoonneEo On Bbed BoE ESEEaGene socecclosee Saddeasase XI oo =~ (Sv) —~1 XII CONTENTS. Part I][—Continued. Page. Chapter XI.—The pre-Carboniferous rocks of the southwestern portion of the Narragansett Basin 381 Little Compton and Newport Neck shales. ---.----.----- =. 202 nee ee en ee 383 Mirena Ou NGO. Shs sae see obo csbaoo spon cooses copy sono bdco cece ocasoses zac srs ostces 383 Chapter XIJ.—The Cambrian strata of the Attleboro district---.---..------.-----.------------ 386 Gambrians brook localities sso s.ssecs sees oc ee eae eee eee Ee ee eye ee ee ees 888 Localities 1 and 2; southwest of North Attleboro. - 22-22 255 22 ees =) ye eee oe 388 Wanbleny Ore loonlbiiny Byes esbn ge secose basa obesdc ones good tosacses sons Shed dooossbosz oso et 392 Locality, 4 northeast of Diamond seul eee er eter ae eee dette ele eye eto 393 Wien as} GhoWél EOBIOMNIEE 565665 badhoo concord doce cosdise sedcos bocaoo NoanSe aodd cade esse asecee sucuaadéser 394 ImVelexs Kadpob Sobbos Skates BoDebb adacaodE aoc0 DGGdGe- bane Sodd Hou maS BoSe SbcS OOD ROGadSSocodé Asad shee 395 PuatTE I, Il. Ill. Iy. We Wale Wants Vill. IX. x. XI. XII. XIII. XIV. XY. XVI. XVII. XVIII. XIX. XX. XXI. XXII. XXIII. XXIV. XXV. XXVI. XXVII. XXVIII. MIX. XXX. XXXI. Hire. 1. EGU SUR IONS. Landscape looking westward across the upper portion of Narragansett Bay, in the lowland of the Carboniferous area, to the base-leveled area of mainly crystalline andipre-Carboniterous TOCks ss. scim oe eigsio ss so oe enim ae neice eseine es eeeeicei=e Pre-Carboniferous rocks at western border, near Providence, Rhode Island .....--- eee Plant-bearing outcrop of Wamsutta group in North Attleboro, Massachusetts ...---.. Faulted diabase dikes in North Attleboro, Massachusetts .......-...--.-----.-------- Rocky Hill, Providence, Rhode Island, a glaciated ridge of the Carboniferous........ Carboniferous sandstones at Silver Spring, Rhode Island. ......---...---.---.-.-.---- Carboniferous sandstones near Attleboro, Massachusetts .--..---..--.---------------- Medium-sized conglomerate, Attleboro, Massachusetts .........--..------------------ Ripple-marked vertical sandstones, Attleboro, Massachusetts -......-..---.--...----- Raindrop imprints on vertical strata, Attleboro, Massachusetts -.......---.---..----- Plainville Valley, Wrentham, Massachusetts. -..........---.---------------- ---- --- ee Vertical bed of Dighton conglomerate at Attleboro, Massachusetts .......---.-------- Near view of Dighton conglomerate, Attleboro, Massachusetts .-.........-..--------- Selected waterworn and indented pebbles from Dighton conglomerate, Attleboro, WIEESMCIMISCBES cbosod cosode abacadosed ones sage cdocsb Sena dba agooEEboeseE meee nace Aeoe Vertical Carboniferous sandstones, Plainville, Massachusetts...-..---...---.-.--------- General view of surface at West Mansfield, Massachusetts.........-..-....-.-..----- Geological map of the northern and eastern portions of the Narragansett Basin...--. Contact of pegmatites with Kingstown shales, Watsons Pier, Rhode Island..--..-..-- Coarse pegmatites of Watsons Pier, Rhode Island -:..-.-...-...--.---.--------+------< Cross-stratification in pebbly sandstone of Kingstown series, Devils Foot Ledge, Rhode lighaingl KooosSodaéonecss sad dnote gsoddcouo cdedou soba debaor oeecad Habousee adse meee Bean Stratification and slaty cleavage, Aquidneck shales, eastern shore of Prudence Island... Wave-cut bench in Aquidneck shales, western shore of Prudence Island_...-.....-.-. Fretwork weathering of Aquidneck shales, Prudence Island........--..---.---.------ Pegmatite dikes cutting Kingstown shales, Watsons Pier, Rhode Island .--......----. Hoppin Hill, a granite mass surrounded by Cambrian, North Attleboro, Massachusetts. Sketch map of the North Attleboro Cambrian localities..............---.---.---.---- Nechiousin) the Narragansett) Bay megion! 2a - mew = settee ala amie = eee) sees sein oe elena eine Sections in the Narragansett Bay region ....-....-........-.-...2--.-.-----------5-- Sections in the Narragansett Bay region ......-..-.-..- se node doSoes Saks SHseDOoOS Geological map of the southern part of the } Nemmnaementh Basin sda soda accu seno canes Diagram of assumed outs iuoas of compressive strain in rocks in a basin of accumu- IGIHION, seedou séaedac codes badd Houo shades caaeouadpBcEneteereseebmodcsedsecec bees sacdos . Theoretical plan of the great folds of the Narragansett Basin -...-....-..-...-.-.---- . Diagram showing misleading synclinal exposures of similar strata....-..--.-.....----- . Exposure of disconnected dike in Lime Rock quarries, Rhode Island...............--- . Sketch map of distribution of upper Cambrian pebbles.-.....--...-...-..---.-2...--2.. . Map showing distribution of metamorphosed Carboniferous rocks. ....-.........-.---- XIV ILLUSTRATIONS. Fic. 7. Map showing general outline of the Narragansett Basin--...-........---.-----.------ 8. Section across eastern arm of the basin.. 7... --.. 2-22. 2-2. 220. en coe oe wee wee ewe 9. Outline map and general cross section of the northern part of the basin. ..........--.. 10. Edward Hitchcock’s cross section of the Carboniferous area.....-......-.---.-------- 11. Map showing distribution of red sediments.....-.-.---..----.------ +++. +--+ +--+ ------ 12. Geological section northward from Robinson Hill........-..---..---.-------.---.---- 13. Diagram showing disappearance of the Wamsutta group in the Coal Measures -.....-- 14. Section through felsite knob in Attleboro, Massachusetts-....-...-.-----.------.----- 15. Geological section in the Millers River region........-...-.-.------------------------ 16. Geological section in the Arnolds Mills region --..........-..-.--..------------------- 17. Hypothetical geological section east and west through Providence, Rhode Island-... -. 18. Folded and faulted Carboniferous shales at Pawtucket, Rhode Island ..........--.---. 19. Sketch of zone of excessively jointed sandstones, face of McCormick’s quarry--.--.-.--. 20. Geological section from Watchemocket Cove to Riverside, Rhode Island......-..-..---. 21. Geological section through rocky islets at Halsey Farm, Silver Spring, Rhode Island. -- 22. Geological section of rocky headland near Silver Spring, Rhode Island.....--....---.- 23. Theoretical section of folded structure on western margin of the Narragansett Basin-- 24. Contemporaneous erosion with unconformity in the Carboniferous at Attleboro, MEEREONNERUUS s55554 056500 556d Hoosnoas sabes ooo b5o09 Sane deen sooo soba SESH sOb0N se80 25. Diagram showine cross bed@in gene pes aese eee nese eee eae ee ee eee een eee 26. Geological section of Plainville Valley and thrust plane.....-..-.-.--..---.---------- 27. Section of the Mansfield Coal Measures ..-.-.......---.--.------------- -------------- 28. Geological section in Westville, Massachusetts..-.---. Scag SS050500 DaG0 sc oo50 sSHosaK6 9. Diagram illustrating the case where boring affords a satisfactory test for coal beds---. . Diagram illustrating the case where trenching affords a satisfactory test for coal...... bw Re Oi TAN SiMe a Ace DEPARTMENT OF THE INTERIOR, Unirep SraTEs GEOLOGICAL SURVEY, Cambridge, Massachusetts, March 2, 1896. Str: I have the honor to submit herewith, for publication, a report on the geology of the Narragansett Basin. This report contains the result of a considerable amount of work done by me or under my direction since I became an officer of the Survey. In part, however, it is the result of studies undertaken before that connection was established. The object of the report is to set forth the results so far attained in the study of a field which presents singular difficulties in the way of its interpretation, and which will require the observation of many other students before it becomes thoroughly well known. Since the preparation of the report was under- taken I have been ordered to extend the results of a general nature there attained to other similar basins on the Atlantic coast. On this account it has seemed desirable to postpone a thorough consideration of many portions of the subject until other parts of the Atlantic coast have been examined. . I have the honor to remain, very respectfully, your obedient servant, N. S. SHaer, Geologist in Charge. Hon. Cuarutes D. Watcort, Director United States Geological Survey. exaVe PREFACE. As the conditions under which this report has been prepared are of importance as explaining the nature and scope of the investigations on which it is based, it is fit that they should be briefly stated. In 1865 I became interested in the geology of the Narragansett Basin, principally for the reason that it afforded a convenient district in which students from Harvard Uni- versity could be instructed in certain problems of field geology which were not well presented in the neighborhood of Boston. A number of the frag- mentary results thus obtained were published in several papers, but the ‘greater part remained unpublished. With the extension of this desultory work a general idea as to the structure of the basin and its relations to some of its more important groups of strata was obtained. In course of time it seemed possible, with a moderate amount of labor, to prepare a memoir on the field which would add something to the body of information concerning the area. : About ten years ago, at the request of Maj. J. W. Powell, then Director of the United States Geological Survey, I undertook to devote the time which could be spared from more pressing duties to the task of completing this monograph. Experience soon showed that the mass of detailed work which remained to be done was so large that it would be necessary to asso- ciate other persons in the undertaking. To Dr. August F. Foerste was assigned the southern or bay section, and to Mr. J. B. Woodworth the north- ern portion of the field. The division of their work was not determined by a precise line, but was left to mutual understanding. Dr. Foerste’s studies began in 1887. They were interrupted after a few months’ labor, but were resumed in June, 1895, and the field studies were closed in September of that year. Mr. Woodworth has from time to time been employed in this field since June, 1891, but the work was discontinuous until the field season of 1895. MON XXXTII— IT XVII XVIIL PREFACE. In allotting these tasks to Messrs. Foerste and Woodworth, I turned over to them the small share of the results that I had obtained in work on this field which seemed likely to be in any way helpful to them. Those contributions were, however, so limited in quantity, at least as regards the difficult matters of detailed structure, that the sections of this mono- graph which appear under their names are essentially their own. A considerable range of facts, especially those which relate to the inti- mate structure and the metamorphism of the rocks, have not been to any extent treated in the following pages. This omission has been designedly made for the reason that the inquiries necessary to a consideration of these subjects would have required the services of a trained petrographer for along time. In a like manner, the very interesting and important vegeta- ble remains which abound in certain parts of the Coal Measures have been passed by, though they well deserved an extensive study. Thus it has come about that the extremely varied rocks which border the Paleozoic stratified series, or which are in the form of islands in its areas, are not dis- criminated according to their lithological varieties, but are indicated merely as pre-Carboniferous, and the paleontology of the basin, which includes extremely interesting groups of fossil insects and other organic remains, is in no wise presented. These and other omissions deprive this monograph of all claims to being a full account of the geological phenomena of the basin; it should, indeed, be considered as a contribution only to the strati- graphical and dynamic history of the area. Where the statements of my collaborators are not questioned by me in footnotes, it should be understood that I approve of them as, so far as I can see, the best that can be made concerning the facts with which they deal. In only one instance has conference failed to bring about a concur- rence of opinion concerning any question of moment. This is in relation to the value of the division which Dr. Foerste has termed the Kingstown series, which he regards as distinct from the Aquidneck, which overlies it. To my mind it appears to be only a local thickening of the last- named series, with a similarly local addition of sandstones. The dis- agreement is not only in relation to the propriety of separating these two sets of rocks, but also as to the thickness of the lower series. It seems to me most likely that the apparent increase in the depth may be reasonably explained by the occurrence of rather compressed folds, the axes of which PREFACE. XIX have not been identified, they being hidden either by the waters of the bay or by the drift covering which conceals the greater part of the surface of the islands. Nevertheless, as Dr. Foerste, who has given much time to the problem, remains convinced as to the distinct nature of this series, it is proper that he should express his convictions in his portion of the report. The matter is clearly debatable, with the probability that the truth is on the side of the observer who has the closest personal familiarity with the field. It may here be observed that the conclusions of this report, so far as they relate to the general structure of the basin of which it treats, are most novel in the matter pertaining to the orogenic history of the field. The judgment as to the nature of the mountain-building work rests in part upon observations—in the main unpublished—which I have made in other somewhat similar basins that lie along the Atlantic coast from Newfound- land to North Carolina. The general proposition that the basins are char- acteristically old river valleys which have been depressed below the sea level, filled with sediments—the sedimentation increasing the depth of the depression—and afterwards corrugated by the mountain-building forces, will derive its verification in part, if at all, from study of other troughs of the Atlantic coast. It may, however, fairly be claimed that the facts set forth in this memoir show that this succession of actions has taken place in the Narragansett field. The contributions to our knowledge respecting the value of the coal deposits of this basin are not so great as might well be expected from a careful study of the field. The truth is that the exploitation of the coal beds has been done in an extremely blundering manner, so that, while a large amount of money has been expended during the last hundred years, the amount of information which has come from it is very small and has little more than negative value. It may reasonably be hoped that the facts set forth in this monograph, and advice based thereon, will serve to prevent other profitless mischances in mining in this area, and make the next work which is undertaken decisive in its results as to the value of these very peculiar coals. The first part of this report is limited to the discussion of certain general topics which could not well be treated in the special reports of Messrs. Woodworth and Foerste. This has necessarily led to a somewhat incom- xX PREFACE. plete presentation of the problems which the basin affords. It should furthermore be noted that the party under the charge of the senior con- tributor is now engaged in studying other basins of the Piedmont or east Appalachian section of the coastal district. From these inquiries it may be expected that there will come a report concerning these peculiar features in the geology of this country. It therefore did not seem worth while to undertake a more systematic inquiry into the Narragansett field, which would demand a larger comparison with neighboring fields than it is possible yet to make. The reader may also remark the fact that there are but few diagrams in the text. Owing to the small and disconnected character of the sections which could be obtained in this basin, it has been found impossible to represent diagrammatically, in a precise way and for all parts of the area, the relations of the strata. Under these conditions diagrams are likely to have a fictitious value—to assert more than the facts warrant. So far as possible, the pictorial representation of the phenomena has been limited to local sections and reproduced photographs. It will also be noted that, particularly in Dr. Foerste’s report, attention is called to a great number of localities which are cited in evidence of the conclusions to which the writer has come. mS & GEOLOGY OF THE NARRAGANSETT BASIN Part Il—GENERAL GEOLOGY By NATHANIEL SOUTHGATE SHALHR MON XXXITI——1 CONTE NS: Page. Cuarter I.—Position and surface relations of the Narragansett Basin, and the rocks it contains. 7 Genera lbteatunen yer esse ere e eer tapes ee ee eect ee ges TN any Rn opel ces 7 Straticnaphicalyandeorogenic relations yer erser seas e ee eee eee eet eee 10 Resultssofstheachonvotoro genic forces sa" eee eee ee en eee eee a 26 Overthrustiph enomen adeseaercccyee ete oer ge cto meerarerateneu Us ee aA nae ai ale A Se rain 25 Dilkemoclesyofytih enh asin caer ee ajc tecty ne Meare nae oe al 2 au load gu URIS GAY Leis yy cae oe 27 CHAPTER eS ehysicalehistony ote theyb asimemes sso) sein mee ee ieee ataiin a acta) el aa ee 30 Relation to marine and atmospheric erosion and deposition....................--..-------- 30 Aveo the\Carbonirerous rocks) ofy they basinisss see eess ese ee eee et ea 36 Original relation of the Narragansett Basin to the sea.-...--....-.....---. 22-22 +22------- 37 Original distribution of the east Appalachian coal field ...... .-..............-.--22-.---- 38 ANnclentimMarcinvotethe basen sah -eeeeee eee eee en eeelene Tacos SeodeEcsorEs wens esa gabeoo 40 Relative erosion of east and west Appalachians --......-......-....---2----2-2-----. eee ee 40 Recent changesiof levels. 22222 5-)2 ee eee BOGS a Bean HES EEA SC EEA s GOaE oSas aeeaS Gone re 46 General statement concerning, base-leveling .-.-.--.----.-----------1---2- 222-22 ee ee eee se 47 Colles ot Gras lee sa cen besa ee sees cons SeeAen SEES ead dase deb laEe SHGOE Suen Se nbedasmese 49 AL Ose; de pOSitLS Ota th oub aginst ers eer teeta oat Tate oy) cl Leela Bie) or ster 50 INSUOINTOSA OE VFRORS 10) ORIOM +o sc'dsa sus eae sasees dace acu aonb ec auonod Saubedouteaeodee 55 IRCCORG! VEINO OF Cone MMe PUES Sse ~sescodueddes sana Scu6 LEGS CHOU Uden cece dod ead wont wees asaee 59 Red color of the Cambrian and the Carboniferous ..-..-..-.--.---.-.--..-.----.+--+----2-- 62 CHarrTeER JII.—G@lacial history of the Narragansett Basin.............-...-....---.-2---------- 64 Warboniferous\con gl omera tes em ee ee pe eee ee este ete ee an 64 WastiGlacialiperiodee= sneer ee eee ae scon oconGcaneq ecu subose Sang bdr asa5o sabe kaucee 67 ANTNOTUT OR OREO Nas CRU aee Ss Soca a Saea nd edie Eat ansia soo uC EE CSE oo a SESE E aaee ae aie meee CEE 71 CHAPTER VEE COnOmIcesounces Otathelbasininse=te ne eee eee eee eee eee ae teem 77 SOS esas Gdcedn ReTO Nes DASH as Bee SEES A Ry eSee eae year Mean GR LN Us cae aca ea 77 CHES Sec0 sana mgunsd Hacseeedaode CHORES SES AAS SSE Here acs ee acorn a Sees as aat a nO a ae 79 Conditionofuth eibedst mean cm same reese ee aarp dare ere Amine mS NL IL 80 CET CUORIKES OP WIS. Gone keoaadad wasueevescoo ache aos ba obeseo Scere SESS cneeanm HenEes 82 COnGhHOns OF Hip CeOMaMNG WO ace sku sass cospoodoedes Sbub bode oeseaoas made BBEe oe 85 Tronjores!|:PlrongerUlide posit vasa m wee soe cs es Stee Sete eal oe ore am a ctolon ars Selene ner ei wele ey oats 88 ie*) LEU S WIR ON Se Page. PuaTE I. Landscape looking westward across the upper portion of Narragansett Bay, in the low- land of the Carboniferous area, to the base-leveled area of mainly crystalline and pre- Warboniferousimoc kismet cctools aaa ote ale alae eel ale ele elo ie ioral 7 Fic. 1. Diagram of assumed conditions of compressive strain in rocks in a basin of accumula- WOM) 042 ob dane conooe cone on ae Hens Coco anes Eons CEeson DoDSEe depconaseous sesees caooannS 19 2. Theoretical plan of the great folds of the Narragansett Basin.-...----.--.-.----.------ 27 = cin fe ar ec ‘ade jpioe|s pue Aieipay aye] jo psoiy ay} ‘ayep Aieiuiay Ajiea yo si uiseq a4} ul puejmo] a4] “Ulseg YesURSeLIeN O84} Jo AsepUNog Ula}sam au} BulWIO; ‘snolajUOqieD o|YdioWe}alU Jo saydzed paploju! pUe ozUe:3 YIM saul||eyshio pajana|-aseq ayy Aq pawoy s! punoldyoeq ayy jo eur) Ays uane ayy "AVG LLASNVOVYYVYN 30 NOILYOd YAddN AHL SSOYODVY ONINOOT MA3IA SH SE | 1 Td IIIXxx HdVHSONOW ABAYNS 1V9I901049 *s “N GEOLOGY OF THE NARRAGANSETT BASIN. Ahi E—-GuNinAkh GHOLOGXY By N. S. SHALEr. Cire AGE une lr POSITION AND SURFACE RELATIONS OF THE BASIN, AND THE ROCKS IT CONTAINS. GENERAL FEATURES. The field which in this monograph is termed the Narragansett Basin consists of a considerable area of stratified rocks ranging in age from the base of the Cambrian to about the later stages of the Carboniferous period. The eastern margin of this basin extends on its northeastern side to near the Atlantic coast in the neighborhood of Duxbury, Scituate, and Cohasset, or, in this section, to within about 6 miles of the sea. Its northern border, including the small Norfolk Basin in the area of Carboniferous rocks, lies in contact with the southwestern wall of what is commonly termed the Boston Basin. On the west the area is limited by relatively high lands which separate the trough from the Worcester syncline, a basin which owes its construction mainly, if not altogether, to mountain-building action occurring after the end of the Carboniferous period. On the south the Narragansett Basin is partially separated from the sea, at least in those portions of it which are above the water level, by a constriction formed of ancient, highly metamorphosed, stratified rocks and a variety of intrusions, together with some granitic areas which are probably of great age. 7 8 GEOLOGY OF THE NARRAGANSETT BASIN. The north-south extension of the Narragansett Basin, meluding the related area of the Norfolk Basin, the axis of its greatest length, is from the southern portion of Narragansett Bay to near Walpole, a distance of about 50 miles. The east-west diameter, from the western part of Cum- berland, Rhode Island, to the town of Scituate, Massachusetts, is about 30 miles. Although its outline has many irregularities, which will be hereafter described, the basin has in general a rudely curved form, concave on the southeastern side. The sections given in a later chapter of this report show that this trough has great depth, the lowest stratified beds disclosed on the margins possibly attaining in its central portions a level of from 10,000 to 15,000 feet below the plane of the sea. The sections also indicate that the correlative anticlines, at least those in the western and central parts of the field, probably had in their original form an eleva- tion comparable in amount to the depression of the great trough which they inclose. In a word, the facts indicate that the mountain-building work effected in this district, and altermg the original reliefs, was consider- ably greater, and gave rise to sharper foldings, than in the more interior parts of the eastern coast of North America, where the elevations still retain the mountainous character. An examination of the structure and attitude of the rocks in this basin, as will be shown in a detailed way in the later sections of this report, indicates that this region originally contained an extensively developed series of pre-Cambrian rocks, the age of which is not yet determinable. They may for convenience be referred to that limbo of ill-discriminated formations, the upper Archean (of Dana), or Algonkian. Above and probably upon the eroded surfaces of these ancient strata, known in this report as the Blackstone series, there lie, apparently in detached, much worn patches, considerable remnants of the Olenellus horizon, or the lower- most stage of the Cambrian. On top of this formation and the granites which have broken through it, which were in turn much degraded, come the Carboniferous beds, strata which, owing in part to their great thickness and in part to their having escaped the nearly complete destruction which overtook the lower-lying beds, now occupy the greater part of the basin. The evidence indicates that, on the western border of the basin at least, the margin of the field was determined before the beginning of Cam- brian time. At the beginning of the Carboniferous, there is proof that GENERAL FEATURES. 9 along the eastern border, trom near the southern end of Aquidneck Island to Freetown, Massachusetts, a distance of 35 miles, a granitic area of considerable extent had already risen above the surface of the sea and was the seat of no little erosion. This is shown by the fact that along this line the rocks at the base of the Carboniferous section are made up mainly of granitic débris, the mass forming a characteristic arkose, at points so resembling the material from which it was derived that it appears at first sight to be the product of simple decay in place. Its age is suffi- ciently indicated by the numerous Carboniferous fossils disclosed by the pits which have been made in the mass in the search for fire clays. It is likely—though the evidence is less indicative than that just noted—that the eastern wall of the basin was in Carboniferous time continued north- ward as far as the neighborhood of Cohasset. The evidence is to a great extent from the drift, and is therefore subject to much doubt. The condition of this basin in the beginning of Carboniferous time was apparently that of a broad trough penetrating far into the land and perhaps, though probably not, extending westward so as to include with- out break what is now the separated basin extending through the central part of Worcester County southward into Connecticut and northward to New Hampshire. The very coarse nature of the pebbly—or, indeed, we may term it cobbly—waste which occurs in the upper part of the Carbon- iferous, appears to indicate that the trough must have been shallow. This conclusion is affirmed by the tolerably uniform distribution of the pebbles, some of them a foot or more in diameter, across the basin on the line from Fall River to Attleboro. On the assumption that the Narragansett Basin was shallow at the beginning of the Carboniferous period, and on the supposition that in the center of the field these beds attain a depth of several thousand feet, it seems necessary to assume that the orogenic work was in part accomplished during that time. The history of the basin can be best explained by the hypothesis of an extensive subsidence of the land within the limits of the trough as the beds which it contains were laid down, and a corresponding overlap invasion of the sediments, which constantly removed the shore lines farther away from the center of the basin. After the close of the Carboniferous period the Narragansett district was evidently the seat of yet further mountain-building actions, which led 10 GEOLOGY OF THE NARRAGANSEDT BASIN. to extensive dislocation of the deposits and to the formation of several anticlines and synclines, as well as to the development of considerable fault movements. In this part of their history the rocks which remain in this field were probably deeply buried beneath accumulations which have been entirely swept away. This fact, as will be shown in detail hereafter, is indicated by the large amount of pebble deformation which has taken place in various portions of this field. The foregoing statements make it plain that the detailed consideration of the Narragansett Basin should be preceded by some study of the strati- graphical and orogenic features of the district in which the basin les. STRATIGRAPHICAL AND OROGENIC RELATIONS OF THE BASIN. The relation of the Narragansett Basin to the system of .disturbances which have affected the eastern coast of North America involves certain questions concerning the organization of the Appalachian system which, so far as I am aware, have never been considered by the students of that field. Those mountains are generally assumed to consist in part of an ancient axis, which was developed perhaps by a succession of movements, partly in Archean and partly in early Paleozoic time, the whole forming a range extending from northern Alabama to the northern parts of New England, with a somewhat obscure continuation through Nova Scotia and Newfoundland to a contact with the old Labrador element of the Lauren- tian Mountains. To the west of the ancient axis of disturbance of the Appalachians, the Allegheny range or series of ranges has been recognized as a development which took place after the close of the Carboniferous, bringing about the formation of some score of considerable folds, all of which, except those in the extreme south, retain their relief. This Alle- ghenian division extends, with diminishing size of folds, as far north as near Albany, New York * West of the Alleghenies, throughout their whole extent, from Alabama to the Mohawk River, there is a table-land which manifestly owes its uplift also to the orogenic work that resulted in the formation of the anticlines and synclines which were produced to the west of the old axis after the ‘It is characteristic of the Alleghenian division of the Appalachians that it consists of prevail- ingly long folds, which are much compressed and generally lie in such a position that an east-west section of the field traverses four or five of the similar anticlines. STRATIGRAPHICAL AND ORUOGENIC RELATIONS. iL close of the Carboniferous period. This table-land is well exhibited in the plateau of central Tennessee, but is most strikingly shown in the degraded remnant of its northern part, known as the Catskill Mountains. It has not yet been sufficiently recognized that to the east of the old Appalachian axis there was a great series of mountain ranges, now obliter- ated, which extended from the southern part of North Carolina along the Atlantic coast as far as Eastport, Maine. The reason why this portion of the system has been neglected is found in the fact that the structures which belong to it are peculiar in form and have been so far worn away that they present no considerable topographical reliefs. The region has the general character of a country which has been brought near to base-level, and the determination of the position of the ridges and furrows can be made only from the attitudes of the rocks. In fact, in the present state of our knowl- edge of this section of the country, only a few of the old troughs are recognizable and the position of the folds is not well made out. Beginning on the south, we find the southernmost of these folds, so far as they have been recognized, in the Dan River Basin of North Carolina. Farther north, the Kings Mountain district appears to indicate the seat of another folding, a part of the rocks involved in the movement being so hard that they have not yet been completely eroded. In the Richmond coal field an extensive series of beds, probably of Triassic or Rheetic age, indicates the presence of another considerable basin, which has something like the area, depth, and general form of the Narragansett downfold. From studies of the Richmond Basin, made at various times, I have become convinced that the depth of the depression in its central parts probably exceeds 3,000 feet, and may be twice that amount, and that, in part at least, it is separated from the sea by an area of uplift which is now worn down to its granitic base. To the north of the James River Valley in eastern Virginia the Triassic rocks are again found involved in relatively deep, broad troughs, the forms of which are not yet well made out. There are probably several of these troughs, some of which contain ancient stratified rocks of undetermined age that may belong in pre-Paleozoic time. From the Potomac River northward, owing to the mantle of Cretaceous and Tertiary waste, we have no distinct indications of this series of foldings until, in New Jersey, we again find the Trias involved in troughs. East of the Hudson the broad 12 GEOLOGY OF THE NARRAGANSETT BASIN. trough of the Connecticut Valley may be regarded as in its nature essen- tially equivalent to the more southern basins, the only substantial difference being that on both sides it is bordered by a wide field of high-lying ancient rocks, which extends eastward nearly to Worcester and has a height that is not found in the case of the walls on the Atlantic side of the more southern basins. At Worcester we come upon the most southern of the troughs on the eastern side of the central Appalachian axis in which well-determined Car- boniferous rocks appear. The form of this basin is not well known, but, from what has been learned concerning it, it appears to be relatively narrow and long, having in general a closer resemblance to the synclines of the Alleghenies than any other of the troughs in the group which we will here- after term the East Appalachians. The Narragansett trough is next in order, but, as it is to receive special treatment, it may here be dismissed with the brief statement that in its type of form and in the nature of its dis- locations it differs from the West Appalachian or Alleghenian series of dislocations. North of the Narragansett district we have in the Boston Basin a con- siderable downfold, the axis of which extends in a prevailing east-west direction, the depression having a characteristically great proportionate width and an irregular form which belongs to the other East Appalachian depressions. From the Boston Basin northward the complicated and imperfectly known geology of the country indicates a succession of these basins dis- tributed along the coast of Massachusetts, New Hampshire, and Maine to the New Brunswick district. One of these occurs at Newburyport; another is traversed by the Penobscot River; others lie between Mount Desert and the outer Cranberry Islands and to the north of the Mount Desert Mountains; yet another, or perhaps two partly separated basins, are to a great extent occupied by Cobscook and Passamaquoddy bays; still others exist along the coast of Maine, though their outlines have not been traced. The Car- boniferous areas of New Brunswick and Nova Scotia appear to have been preserved in basins having the general character of the East Appalachian troughs Reference has already been made to the decided differences in the forms of the folds which occur on the two sides of the old Appalachian axis. STRATIGRAPHICAL AND OROGENIC RELATIONS. 13 Those on the west are narrow, relatively long, and consist, with slight exceptions, of simple foldings of the true anticlinal type. Those in the eastern or seaboard district are in general rudely oval in form, their length usually not exceeding twice their width. They are, in fact, broad troughs, the included strata being cast into a number of anticlines and synclines. This peculiar difference of form leads naturally to the supposition that the history of these two groups of depressions has been diverse. An inspection of the deposits verifies this supposition. It has already been stated that the Narragansett Basin was an ancient trough, formed before the Carbon- iferous period, in which, during a process of subsidence, the beds of the Coal Measures were accumulated. The evidence derived from the study of the Richmond, the Connecticut River, the Boston, the Mount Desert, and the Passamaquoddy basins has satisfied me that the troughs are of ancient date, that they were filled to a considerable extent with materials imported from the higher country about them, and that this filling process was associated with progressive local subsidences. The foregoing considerations seem to me to warrant the supposition that the East Appalachian basins, or at least the greater part of them, were, in the beginning of their formation, erosion troughs, which became the seats of excessive deposition, and this brought about the lowering of their surfaces in relation to the original bed. In a word, they were downpressed by the weight of the burdens which came into them. Ata subsequent stage the mountain-building forces, acting irregularly, compressed these troughs, producing the sets of local disturbances which are exhibited by each field. A possible instance of such local orogenic action in very modern times, as late as the Pliocene, is found in the tilted strata of the Marthas Vineyard district. In this case excessive deposition of a local character has been followed in turn, first, by subsidence, and then by com- pressive action, producing a large measure of folding, in a general way like that which has taken place in the neighboring Narragansett Basin, which lies immediately on the other side of the anticline that forms the eastern boundary of the Narragansett trough. It should be said that the hypothesis of the antecedent erosion of the basins which we are discussing has a considerable measure of support from the very diverse orientation of the axes of the East Appalachian troughs, These range from east and west to north and south, a diversity which 14 GEOLOGY OF THE NARRAGANSETT BASIN. seems to me to be inconsistent with the supposition that they have been formed through the action of such accurately determinate strains as produced the Alleghenian ridges. The last-named foldings are of the normal mountain type. The axes are parallel for great distances, and where the ridges change their orientation they preserve their parallelism and alter their general course with rather gentle curves. They exhibit no case of such contrast in the axes of the basins as is shown in the adjacent Narragansett and Boston troughs. The known facts concerning the effects arising from the accumulation of thick sediments warrant the supposition that wherever this action occurs it is likely to be attended by a subsidence which, though of a local char- acter, may attain an extent proportionate to the influx of the débris. Wherever along the coast line long-continued land erosion forms deep valleys, these depressions are likely to be, during a period of subsidence, the seats of extensive deposition. Where the amount of this sediment is sufficient to develop the downcast movement, it may lead to the formation of a trough of great geological depth, though it may at all times be shallow water or even retain the state of a delta area. It therefore does not seem a matter for surprise that the Atlantic coast district should exhibit basins of this nature, for, although this coast of the continent has been subject to many alterations of level, there is abundant evidence to show that from the Cambrian period to the present day the eastern front of the land has been often, indeed we may say prevailingly, somewhere near its present position. There has been ample time for the formation of many great coast erosion troughs and for their fillmg with sediments to the amount which the hypothesis requires. The final development of anticlines within the troughs in the extensive way in which they appear to have been formed may readily be explained by the existence of the same compressive tensions which have operated in the West Appalachian field, the difference being that in the East Appalachians the form of the troughs somewhat controlled the direction of these anticlines, while in the western portion of the system, a newly emerged part of the continent, they appear to have been guided in their alignment in a much greater measure by the direction of the com- pressive strains, there being no strong topographical features except the old land on the east to determine the trend of the upeurving. At the present time, although the Atlantic coast of North America has CONDITIONS OF DEPOSITION OF BEDS. 15 been subjected to recent and important alterations of level, there are many considerable basins along its shores which appear to be, in their structure and history, much like those which, according to the hypothesis we are discussing, were developed along this coast line during the Carboniferous period. Albemarle and Pamlico sounds, and the bays of the Chesapeake and Delaware, need only a continuance through a considerable extent of geological time of the conditions which now exist to bring about the formation of accumulations essentially like those under consideration. So, too, certain basins along the Gulf of Mexico, particularly Mobile Bay and the trough of the Mississippi, are the seats of extensive estuarine accumula- tions which in the ages to come may take on much the same aspect as the Narragansett Basin. A little consideration will show the reader that a river valley in its lower parts naturally becomes the seat of sedimentation. An inspection of the maps of shore lines will make it plain that more than half the great rivers of the world have the lower parts of their valleys flooded in a way which clearly indicates that these estuarine regions have recently been brought beneath the level of the sea and thus converted from fields of erosion to those of deposition. The generality of the fact that the great rivers, notwithstanding the evident tendency to accumulate delta deposits about their mouths, enter the sea through their own submerged valleys, is probably in many cases to be accounted for by the fact that, while the con- tinental masses as a whole tend rather constantly upward, their shores, being near the seat of maximum sedimentation, naturally tend downward, in the manner now recognized as resulting from the imposition of a great load of sediments on any part of the earth’s surface. We may therefore regard the occlusion of river valleys by excessive sedimentation, which takes place coincidently with the subsidence of the trough below the level of the sea, as a normal feature in the history of any shore which is intersected by river valleys. If the hypothesis which is here adduced to explain the main peculiar- ities of the Kast Appalachians be established, it is clear that, considered from the point of view of their origin, we must accept a new specific group of mountains, one characterized by features in the main determined by the fact that the beds of which they are composed have been laid down in a formerly existing erosion basin, originally due to stream work, though it may 16 GEOLOGY OF THE NARRAGANSETY BASIN. have been orographically deepened by the su psidence caused by sedimenta- tion. It will be seen that this view has a certain superficial resemblance to the hypothesis commonly known as James Hall’s, in which mountains are explained by supposing, first, the accumulation of a thick series of beds; second, a subsidence of the crust, due to the deposits, bringing about a folding of the beds; third, a massive uplifting of the foundation on which these foldings rest, so that the ridges come to stand on a lofty pedestal. I would not have it supposed that there is any real similarity between these hypotheses. The essential difficulty of the hypothesis which endeavors to explain the formation of mountains first by subsidence and then by eleva- tion, is that there is no sufficient means indicated whereby the reelevating process can be brought about. There is also much reason to question whether the downsinking movement could develop the arches of the strata. In the view which I am advocating, the conceptions are much more simple and rest upon more patent facts. The steps of action which are postulated are as follows: First, the excavation in ancient and compact rocks, in their nature good transmitters of thrusts, of a trough or basin such as is likely to be formed in the estuarine section of a considerable river; second, the filling in of this basin by sediments accumulated during a downward oscillation of the area in which the basin lies; third, the development of compression strains, such as are involved in rock folding, the relief being afforded by the folding of these stratified deposits. If this hypothesis as to the origin of the Narragansett foldmgs were correct, we should expect to find the maximum of disturbance in the extreme margins of the basin, the central features of the area remaining less dis- turbed. As will be seen from the chapters on the deposits of the basin, this is essentially what we find. Wherever the area is of sufficient width to afford a field for the development of the structure in a clear way, we observe that the indications of lateral stressing are very clear in the belts of country next the contact with the crystalline rocks, while in the central portion of the field the beds exhibit lessened stress. Thus, as will be seen from fig. 1 (p.19) and the sections across the basin where the distance is not far from 20 miles, we find the marginal portion of the stratified rocks exceed- ingly flexed, the resulting dislocation attaining about the highest order of complexity, while the intermediate field, including much more than one-half the whole length of the indicated line, is less marked by the stressing forces. STRATIGRAPHICAL AND OROGENIC RELATIONS. 17 Where the Narragansett Basin narrows, as it does in the southern third of its length, the type of the folding differs somewhat from that above indicated. In place of the folds on either side, with a less disturbed middle field, the whole of the section is folded into a few great trough- shaped undulations, with some minor irregularities. Yet the fact that the strains entered the bedded rocks from the sides is shown by the character of the bottom of the great North Aquidneck syncline. The form of this part of the basin is tolerably well known by the mine workings in the northern part of Aquidneck Island. These explorations show that the cen- tral portion of this area has in a measure escaped. the disturbing influences which have perturbed the beds next the margins. Besides the evidences of stress which are shown by the extensive dislocation of the stratified rocks of the Narragansett Basin, we must note the equally characteristic marks of compression afforded by the interstitial movements which the rocks have undergone. These changes of position of the rock materials are exceedingly common in the metamorphic part of the field (see fig. 6, p. 120) and for a short distance to the eastward, and are readily observed wherever there are any data by which they may be judged. Wherever the rocks lying near the eastern and western margins of the basin contain organic fossils or pebbles, save of quartz, a slight examination will in practically all cases show that those bodies have been more or less elongated, the direction of their extension usually being on horizontal lines which are approximately parallel to the neighboring margin of the basin. At many points it is evident that the elongation of the pebbles or fossils has been as much as 50 per cent of their original diameter on the given axis, and sometimes it exceeds this amount. It commonly happens that the distortion was sufficient to convert a circular disk lying in the axis of the movement, and having a diameter of a foot, into an ellipse having a major axis of 2 feet and a minor axis of 6 inches. In rare instances the alteration of form appears to go much beyond this proportion. I suspect, mdeed, that at a few points it is obscurely traceable to three or four or even five times the original length, but in these higher terms of the series fossils become mere blurs and pebbles lose all semblance of their original character. Although solid bodies like quartzite pebbles may often be found stretched to the amount of 50 to 100 per cent, it is generally easy to see MON XXXIII——2 18 GEOLOGY OF THE NARRAGANSETT BASIN. that the matrix in which they are embedded has been much more extended than the more rigid inclusions. This is shown by the fact that near each end of the axis of the pebble in which the elongation has taken place there is often a slickensided surface, showing that the matrix pulled away from the sides of the stone and slipped by them, while at the very end we note the existence of a vein deposit which is also slickensided after the manner of most veins, the structure showing that the movement which pulled the matrix away from the inclosed fragment operated slowly and by successive steps. It often happens that pebbles, especially those of large size and of the more rigid varieties of stone, show no distinct signs of elongation, and yet they have these appended veins and the slickensides, indicating that the more plastic matrix has yielded to the pressure which has been imposed upon it. There are certain features in the distribution of elongated rock masses which appear to throw some light on the questions we are now considering. In the first place, we note that in the Narragansett Basin, and, so far as my observations go, in the other basins of the East Appalachians as well, the plastic migrations of the strata, as shown by the distortion of fossils and pebbles, are decidedly more common in the marginal parts of the several fields. These elongational phenomena are strikingly manifested at many points in the southern portion of the Narragansett area. In the central part of the area there are extensive tracts of conglomerate where a close examination has failed to indicate either that the pebbles were stretched or that the matrix was forced by these inclusions. This goes to show that the force which affected the stratified rocks came upon them as a thrust hori- zontally transmitted from the field of crystallized rock on either side. The other point concerns the regional distributions of plastic migration of rock. This phenomenon seems to be of common occurrence in the East Appalachians from New Brunswick southward. It is excellently shown at the Cobscook Basin, about Mount Desert, and in the Boston Basin; in the basins to the southward it is more scantily exhibited. Curiously enough, however, this feature appears to be prevailingly lacking in the rocks of the West Appalachians, notwithstanding the deposits of that section appear to have been on the average about as much dislocated by folds and faults as have those of the eastern section. It is not clear to what the greater plastic movement of the eastern rocks has been due. It may, however, be sug- gested that such movements depend upon the compression of rocks while STRATIGRAPHICAL AND OROGENIC RELATIONS, 19 under a deep cover of overlying strata and therefore at temperatures which would in a large measure diminish their rigidity. This does not seem a satisfactory explanation, for the reason that while the amount of strata which has been removed from these eastern mountains has probably been larger than is the case with the western ranges, the erosive process, at many points in the west, has gone far enough to reveal the bases of the anticlines and synclines, even as it has done along the Atlantic coast. It has been noted that the eastern basins are generally, except perhaps that of the Dan River, much more intersected by dikes and stocks than are those of the west, where there are but few such intrusions known, perhaps in all not over a dozen between the Catskills and Ala- bama, as against the thousands which may be traced in the moun- tain-built area of the Atlantic coast. It seems reasonable to assume Fig. 1.—Diagram of assumed conditions of compressive strain in rocks in a basin of accumulation. AA, massive crystalline rocks. BB, the rocks of the basins. The arrows indicate the direction of the compressive strains; the spaces between their heads indicate the measure of the yielding at the several points. that the extensive plastic move- ments of the rocks in the East Ap- palachian district are related to the igneous action which has occurred in this field, and that the two groups of facts show that the modes of action of the mountain-building forces in the two districts were in some ways very different. I venture to suggest that the difference was partly due to the conditions of the superficial rocks in the two fields. In the west the surface of the country from northern New York to Alabama was, at the time of the elevation of the West Appalachians, again occupied by relatively unbroken strata which lay on the surface of the upper Paleozoic rocks. The stresses of compression which assailed this wide field when the conditions of resistance were uniform affected all parts of it in al approximately equal degree. In a limited way, in northern Alabama, Georgia, and Tennessee, where the conditions were diversified, the stresses, as shown by Hayes, were in some cases locally accumulated and so discharged as to bring about extensive overthrusting; but in general the folding was approximately equal for each unit of the section which was stressed. ‘There was, in a word, no transfer of thrust through great beams of massive and therefore unyielding rock to fields where the stress could take effect on the easily folded strata. On the Atlantic slope, however, the conditions led to the local intensification of the stress phenomena. Between the deep basins, 20 GEOLOGY OF THE NARRAGANSETT BASIN. filled with their bedded rocks, lay fields of crystalline materials which had been compacted by previously administered pressures and the accompany- ing metamorphism until they had been brought to the most rigid or the best thrust-transmitting state to which rocks may attain. The result was that the compressive strains were transmitted through these ancient close- knit blocks of strata to take effect on the frailer materials which were inclosed in the troughs between their edges. The assumed conditions are in a diagrammatic way represented in the accompanying figure (fig. 1). RESULTS OF THE ACTION OF OROGENIC FORCES. So far as can be determined by the evidence which has been found, the orogenic movements which flexed and fractured the Carboniferous rocks of the Narragansett Basin did not affect in a similar manner the more ancient formations which border the area. ‘There are, it is true, certain faults intersecting the margin, particularly on the northern side of the area, whick cut through the Carboniferous beds and the fundamental complex alike, but there is no evidence that these faults extend very far beyond the margin or that folds attended the formation of the rifts. Any system of anticlines and synclines affecting the more ancient beds would, we may fairly presume, have left their marks in the distribution of the deposits as they appear on the present surface. The several groups of metamorphosed beds would appear in parallel bands, an arrangement which they do not exhibit. The only distinct feature in the ancient compact rocks which can be attributed to compressive action is the system of shearing planes which have been extensively developed in the massive rocks on the margin of the basin. Where these have been developed in the granitic rocks they have given the latter a gneissoid aspect. These secondary structures are most distinctly marked near the contact borders on the east and west, and appear to diminish as we pass a few miles from the present margin of the Carbon- iferous field. The existence of this class of distortions in the rocks, along with the general lack of evidence of folding, poimts to the conclusion that the pressure affected these compact formations in a way different from that in which it affected the stratified beds of the basin. It may be that the yielding in the interstitial movements accomplished a certain reduc- tion in the length of the sections even when the materials were too rigid RESULTS OF THE ACTION OF OROGENIC FORCES. al to permit them to take on the normal folds which afford the natural means of shortening in stratified beds. Since the shearing planes of the massive rocks grow less evident as we go away from the margin of the basin, and have not been clearly observed beyond the limits which are likely to have been occupied by its deposits, the question arises whether these planes are not a consequence of the movements which must have occurred in the rocks that lay beneath the Carboniferous strata at the time they were folded. That some form of distortion affected these basilar deposits must be assumed, but the precise nature of the movements is not known. The type of folding exhibited in the stratified rocks of the basin is clearly that of ordinary synclines and anticlines which have been carried to a rather advanced stage of development. As will be noted from the maps, the axes of these folds trend nearly north and south in the southern portion of the basin, but in the northern part they incline to the eastward, and in the east attain a position nearly at right angles to the southern folds. This turn of the structural axes seems to be due to the existence of the broad eastern bay, which is a notable feature of the basin. There is another noteworthy feature in the form and distribution of the anticlines which appears to be closely related to the peculiar history of this basin; this is clearly exhibited in the accompanying diagrammatic section (fig. 2, p. 27), which shows the attitudes of the folds in the central part of the field along a line from north to south. In this section the compressive action has operated to create strong folds next the borders of the basin. These folds have their steepest slopes toward the margin, the sides toward the center of the basin being much less inclined, so that by erosion of the declivities of the anticlines on either side a relatively broad trough is formed in the central part of this field. So far this relation of the slopes of the upper folds to the margins of ancient massive rocks has been distinctly traced only in the northern half of the mountain-built district, but there are indications that it exists also in the southern portions of the field, being there concealed by the waters of the bay or masked by the prevailing covering of drift. The disposition of the strata as above noted appears to require the supposition that the thrust acted from either side in such a manner that the central portion of the basin was a relatively neutral zone in the vaulting Do GEOLOGY OF THE NARRAGANSETT? BASIN. movements. If the strain which produced the folding was of equal value in all parts of the basin, there would be no reason why the resulting arches of the strata should not have been of uniform declivity on either side. I can best account for the facts in this case by supposing that, while the contraction which brought about the mountain building may have acted in all parts of the field, a large part of the stress was carried through the lateral girders of indurated massive rocks on either side of the basin until it could be applied to the newly formed, distinctly layered, and therefore less resistant materials contained in the old Narragansett Basin. The horizontal value of the movement which was taken up in the fold- ings of this field can not as yet be accurately computed. The attitudes of the beds, however, indicate that it amounted to 2 miles or more. ‘The con- ditions of this action may be considered as such that the surface of the cen- tral part of the disturbed area may not have been moved except down- wardly, while the longitude and latitude of the points on the surface on either side which were affected by the foldings were evidently changed in an increasing measure as we depart from the central axis. The depth of the distinctively stratified rocks in the basin at the time the mountain-building work was done can not well be reckoned at less than that of the existing section, but as this region has been subjected to an amount of erosion competent to bring the anticlines and synclines to about the same level, it may well have been near double that amount. Therefore we may assume the depth of the section of massive rocks which conveyed the thrust from an extreme area on either side to the deposits of the trough as not less than 2 miles. It is not yet clear whether the mountain-buildimg action which has affected this basin was altogether accomplished after the latest-formed beds which it now contains were accumulated. The factthat all the sections of the Carboniferous series were accumulated in shallow water, or but little above its level, requires us to suppose that the trough was the seat of a nearly continuous depression. It is to be expected that the downsinking would have been accompanied by some measure of compressive movement. So far, however, the field has afforded no evidence of such mountain-building work done during the subsidence of the trough. On the contrary, the observations are most reconcilable on the supposition that the whole of the strictly orogenic action took place after the work of depression was RESULTS OF THE ACTION OF OROGENIC FORCES. 23 complete. In fact, it can not be believed that there was any distinct rela- tion between these two movements—that of general downsinking and that of warping under the influence of the lateral tnrusting. It may be noted that the conditions of mountain building in this basin resemble in a general way those of the Appalachian district, with the excep- tion that in the latter region the neutral axis appears to have been in the line of the ancient belt of the Blue Ridge or its equivalent ranges to the north and south. Against this central ridge the thrusts apparently came from the east and west. Moreover, in this Appalachian field the com- pressive action seems to have been distributed over a much wider section, with the result that the amount of deformation per unit of length in an east-west direction was much less than was the case in the Narragansett Basin. The folds are, on the average, less crowded together, and the synclines are wider; in other words, the evidence goes to show that, in proportion to the size of the disturbed area, much more movement was taken up in folds in the Narragansett Basin than was the case in any part of the West Appalachian field of disturbances. The relation of the mountain-building work of the Narragansett Basin to similar action in the neighboring fields is a matter of much interest. There are three of these areas that deserve special notice—the Connecticut Valley, Marthas Vineyard, and Boston Basin. Of these three regions of mountain-building action, the one most remote—the Connecticut—is in all respects the most unlike the Narragansett Basin in its orographic features. In the Connecticut Basin we have what appear to be the same general antecedent features noted in the Narragansett Bay. ‘There was a preex- isting valley, which was deeply and rapidly filled by detrital materials. It is likely that this accumulation took place during a period of subsidence; it evidently occurred after the deposits of the eastern trough had been formed, and under conditions which led to the extravasation of large amounts of lava. When the Connecticut Basin was subjected to compres- sive action, the yielding was by the rupture and shearing of blocks, with little trace of folding. It seems most probable that the hypothesis adduced by Prof. W. M. Davis—which is, in effect, that the easily fractured planes of the basement rocks of the area, which are composed of schists standing at a high angle, induced the formation of faults rather than folds—accounts for the departure of this region from the type of mountain building else- 24 GEOLOGY OF THE NARRAGANSETT BASIN. where to be observed in the New England troughs. In a measure, the dis- tinct folding of the neighboring trough deposits on the east, occurring where the basement beds are of an essentially nonschistose character, seems to bear out this hypothesis. In the Marthas Vineyard area of distortions there is no indication of atrough. There are no ancient rocks rising above the plane of the sea. Itis, however, quite possible that the northwestern border of the basin, if we assume such to have existed, was in the bed rocks of the neighboring main- land and that the seaward border has been worn away by marine action or lies depressed below the sea level. It is to be noted that the prevailing axes of the dislocations on Marthas Vineyard indicate a pressure acting from the northeast and southwest, with resulting foldings which are mainly aligned in a northwest-southeast direction, or approximately at right angles to the usual trends of the Narragansett and other folds of this part of the continent. Although it seems to me probable that these crumplings of the Cretaceous and Tertiary beds of Marthas Vineyard were formed in a trough which was filled in these ages, the evidence on this point is not clear. So, too, with the dislocated deposits of Block Island. It will there- fore be best to pass these areas by with the remark that the forms and trends of their orographic reliefs differ widely from those of the older dis- turbances, and that some of their peculiarities, especially the faultings and complications of their folded strata, may be due to the fact that the move- ments occurred near the surface, without the restraint which is imposed on beds, such as those in the Narragansett area, compressed while under a thick mantle of deposits which have since been removed. In the Boston Basin we find series of rocks which have the same general character as those in the Narragansett Bas. 'To a great extent, the rocks, as regards their structure, are fairly comparable to those in the Narragansett district. Although the evidence is not perfectly clear, it goes to show that there was the condition of a preexisting basin, which was formed sometime after the horizon of the pre-Cambrian, and which received the deposits of the Roxbury conglomerate period, which make up the greater part of the accumulations. As yet the age of these conglomerates and the associated rocks is not determined, a most assiduous search having failed to reveal fossils of determining value. Therefore it is not possible to fix the earlier limit of the disturbances. Still, the immediate contact of the OVERTHRUST PHENOMENA. 2d basin on the north and south and the approximate parallelism of the axes of their foldings appear to indicate that the strains took effect on them at approximately the same time. Complicated as is the structure of the Narragansett Basin, that of Boston Bay is yet more involved. Although some minor folds may be traced in it, and larger arches are fairly to be assumed, the area as a whole appears to be much less massively and continuously flexed, and more faulted, than that on the south. It is, moreover, far more generally penetrated by dikes than is the Narragansett field. Its type of structure seems to be between that of the last-named basin and that of the Connecticut. It is probably owing to the relatively deep erosion of the Boston Basin and the large amount of faulting in the orogenic work that it is so difficult to recognize and determine the elements of foldmg which have existed. OVERTHRUST PHENOMENA. The phenomena of overthrusting which occur in the development of mountain dislocation have of late been the subject of much profitable inquiry. It is therefore worth while to examine into the question of their occurrence in this basin. As will be noted in the sections, the only portions of the field where accidents of this nature seem to be indicated are in the district extending from near Providence to the northern boundary of the basin. The reason for this may be that only in this part are the attitudes of the rocks near the margin sufticiently disclosed to make a close interpretation possible. Particularly in the region about the Attleboros the positions of the dislocated strata favor the view that the beds have been at first folded and then thrust over, usually toward the less-disturbed centers of the stratified rocks, so that a certain amount of migration of the beds has been brought about. How far this has led to the disruption of the folds, so that the masses which have changed place have been rent away from the beds of which they originally formed a part, can not be determined from the data now in hand. It is probable that the original margin of the Carboniferous rocks in this basin was farther away from the center than it is at present. The process of erosion, which has attacked the massive crystalline rocks of the boundaries as well as the stratified interior parts of the trough, has most likely lowered the whole of southeastern Massachusetts to the extent 26 GEOLOGY OF THE NARRAGANSETT BASIN. of several hundred, perhaps to the depth of 1,000 or more, feet, the result being that, as the old bordering walls had an erosion slope, the margin is at present perhaps some miles nearer the center than it was when the folding was done. It has also been noted that the folding and other evidences of stressing which the rocks present diminish, except on the northern border, as we pass from the margin toward the interior of the Carboniferous area. These considerations lead us to see that the portions of the beds which were most dislocated have been removed by the erosion process, which, as is shown by the planed-down character of the surface, has undoubtedly been very active in this part of the continent. It is therefore not unlikely that great migrations of strata took place at the time of the disturbance, the indications of which have been entirely lost to us by the process of decay and removal of the beds which were involved in the movements. In a word, the zone where we might most naturally suppose the overthrusting actions to have taken place has in large part disappeared, at least so far as the superficial beds are concerned. From the conditions presented by this basin there is reason to believe that the rupture and horizontal displacement of folded strata would be more likely to occur here than in the ordinary instances of mountain folding. Under the usual circumstances, where the contracting impulse affects < large extent of country, influencing all the rocks alike, the relief effected by the corrugations of the strata is apt to be equal in all parts of the area subjected to the movement. When, however, as in the Narragansett dis- trict, the strains were most applied on the margins of the field, where the tensions developed in a wide extent of country were localized in a narrow zone of relatively weak strata, we must expect the highest type of distortion and rupture that occurs in mountain-folding work. Such overthrusting as has occurred in the Narragansett Basin appears to a great extent to have been begun by folding, the arches being raised to a considerable height. These arches appear to have collapsed, as all com- pressed arches tend to do. Overthrusting action appears to be most probable in the region between the villages of North Attleboro and South Attleboro, where the relation of the red Wamsutta series to the gray rock on the south requires the supposi- tion of this movement. So far as has been observed in the few traceable OVERTHRUST PHENOMENA. PAT = faults, there is no tendency of faulted blocks to ride over one another. It can readily be understood that, inasmuch as this region has been subjected to very extensive erosion, overthrusting which was preceded by the collapse of the folds might have all the marks of its former existence destroyed by the removal of the strata which were involved in the movement. An ideal section (fig. 2) drawn by Mr. Woodworth through the three great synclines in which the Dighton group appears, including the Attleboro syncline on the north, the Great Meadow Hill trough in the middle of the basin, and the Swansea syncline on the south, exhibits a symmetry in the cross section which is further evidence of the simplicity of the larger features of structure of the central part of the basin. here is along this line of section a great broad syncline in the middle of the basin. It has nearly symmetrical slopes with relatively low dips. ‘The synclines parallel Attleboro Gthheadow S1// Swansea syaclines syncline synclin e ~ A Pr Sra a Fic. 2.—Theoretical plan of the great folds of the Narragansett Basin. with it on the north and south have their axial planes inclined away from the middle synecline, or, in other words, the sides of the synclines facing the middle area are nearly vertical. A plane lying in this region of folding would have been deformed so as to give a cross section like that in fig. 2. There is in this case no prevailing pitch of the axial planes to or away from the ocean or an older land mass, but rather a symmetrical deformation of beds with reference to the middle line and sides of the basin as it now exists. DIKE ROCKS OF THE BASIN. Although, as before stated, the systematic study of the igneous rocks of this area has not been undertaken, there are certain features connected with their distribution which deserve notice. ‘These concern the areas in which the intrusions occur and the portions of the great section which they traverse. 28 GEOLOGY OF THE NARRAGANSETT BASIN. So far as has been observed, all of the numerous intrusions occur on the marginal portions of the basin, mainly on its western side and in the prolongation of the area in what is known as Norfolk Basin, a field which, as elsewhere noted, is not much considered in this report. The eastern margin of the area is not so well revealed as the western, but, as will be seen in the detailed descriptions of Messrs. Foerste and Woodworth, with the exception of the felsite dike in Plympton, no mtrusive masses have been discovered on this margin. Dikes also occur, as indicated in Dr. Foerste’s reports, on the southern portion of the field, but not so abundantly as on the western versant. So far as the observations go, they make it improb- able that, in general, any dike attains the surface at a poimt more than 2 miles toward the interior from the border of the Carboniferous field. An exception to this statement must be made in the case of the Wamsutta field, where, perhaps owing to the large amount of disturbance the beds have undergone, dikes are found at a distance of nearly 4 miles from the western border. It may also be remarked that the extended study of the rocks in the central portions of the area has shown that, while dikes may perhaps have penetrated to the lower parts of the section, there is no evidence afforded by the bare rock surfaces, or by the materials of the drift so far as observed, which would lead to the supposition that these injections penetrated into the zone of the upper conglomerates. Perhaps the most interesting group of what appear to be intrusive masses is that of the pegmatites which occur in the southern portion of the western margin. As we go southward from Providence there is a gradual increase in the measure of metamorphism to which the Carboniferous strata have been exposed. The observer is led to suspect the existence of some extensive concealed intrusion which has applied much heat to the section. These indications of metamorphism increase until they attain their maximum in the portions of the field in and about Boston Neck and Tower Hill. Where the alteration of the strata is most considerable—where, indeed, those beds appear as ordinary gneisses—we find extensive pegma- tite intrusions, which penetrate these conglomerate and sandstone gneisses. I have been unable to determine whether these intrusions are to be classed as dikes or as veins. So far as observed, the facts hardly warrant the assumption that the metamorphism is directly due to the incoming of the DIKE ROCKS OF THE BASIN. 29 pegmatites, but rather lead to the supposition that these last-named deposits have been derived from some large granitic mass intruded into the basement rocks of the section, though at no point exposed on the surface. The facies of the beds in the region about North Attleboro makes it appear not unlikely that volcanic action may have taken place in this por- tion of the field. CoH ASRAD Hie agli PHYSICAL HISTORY OF THE BASIN. RELATION TO MARINE AND ATMOSPHERIC EROSION AND DEPOSITION. It may well be noted that the degree to which shore land basins, such as we are now considering, are developed is in general determined by the amount of time during which a given coast line has remained in about the same position. It is not to be supposed that the coast level remains endur- ingly the same, but rather that in the repeated oscillations the sea does not long desert a given field. During the periods when the area is relatively high the rivers in the lower part of their courses have a chance to develop those wide valleys of gentle slope which are characteristic of regions that have attained very nearly to the general base-level of erosion—1. e., the average position of the sea during its endless variations in height. In general it may be said that wide valleys next the shore are the best possible indications of a relatively long continued preservation of coastal conditions in the region where they appear. The Atlantic coast of the Americas affords numerous examples of these broad, nearly base-level valleys, which have been formed at divers times in its history. As the existence and the number of these valleys have a distinct bearing on the problem in hand, it is worth while to give a brief general account of them, at least so far as North America is concerned. Along the Gulf of Mexico there are half a dozen of these considerable troughs, of which those of the Mississippi and Mobile rivers are the most characteristic, or at least the best known. Both of these valleys, and probably the other basins along this coast, are, at least as regards their lower parts, of relatively modern origin, dating probably from Tertiary times. On the Atlantic coast, to the north of Florida, there are again a number of these lately formed basins, of which those of Albemarle Sound and Chesa- peake and Delaware bays are the largest and most characteristic. 30 STRUCTURAL DEPTH OF BASIN. 31 North of Delaware Bay, and thence along the coast to Greenland, the number of distinct coast erosion troughs increases and the evidence of their great antiquity is very clear. The position of the Newark deposits in the Connecticut Valley makes it evident that this region was an eroded basin as far back as the Triassic period. The Narragansett Basin owes its excavation to actions which antedate the Carboniferous. The Boston Basin, and several others to the northward along the shores of Maine, may be dated back to the Paleozoic age. Yet farther northward, wide valleys of the coastal-plain type, though now deeply submerged, are indicated by the reentrants of the Bay of Fundy, the Gulf of St. Lawrence, and prob- ably by the great system of embayments of the Aretic realm, the Greenland Straits and Hudson Bay, as well as by a host of lesser indentations, which probably mark the seat of long-continued or, rather, frequently repeated river action interrupted by periods of marine invasion. It will be observed from the statements made in this report that the Narragansett Basin has at present an average structural depth of probably not less than 7,000 feet and a maximum depth of 12,000 feet; that is to say, the downfolded Carboniferous rocks and the beds which lie beneath them attain, at the base of this incline, a position at least the last-named distance below the present sea level. The question arises as to how much of this geological depth is due to erosive work on the rocks of the area and how much to actual depression preceding or connected with the folding of the strata. If the basin originally had anything like its present depth, we should have to suppose a very great change in the position of the coast line. If, on the other hand, we may assume, as is done in this paper, that the basin, as regards its geologic depth, is mainly the product of folding, and that the movements are probably due in the main to the accumulations of deposits, then the original depth of the basin may have been slight. The evidence seems to show that the coastal basins of the Atlantic shore owe their depth to three more or less associated actions—to river erosion, to downflexing and faulting associated with the accumulation of strata during periods of subsidence, and to the massive swing of the conti- nent in those large deformations such as have taken place in recent times, with the consequent invasion of the sea into the valleys. Two of these actions are local in their nature; the third involves continental or perhaps wider conditions. By GEOLOGY OF THE NARRAGANSETT BASIN. It should be said that the mainspring of the development which has taken place in these basins is the crustal strain which manifests itself in mountain building. Where this strain, as in the ordinary conditions of mountain growth, such as existed in the West Appalachians, takes effect on uniform, horizontal, little eroded strata, the action appears to result in the formation of elongated, more or less accurately parallel ridges, such as are exhibited in the Jura or the Alleghenies. Where, on the other hand, as along the Atlantic coast, the crust is composed of ancient massive rocks in which deep valleys have been excavated, the orogenic strains result in the deformation of the patches of stratified rocks which may have been accumulated in the great valleys during the periods of subsidence. The dislocations of the Atlantic coast basins clearly indicate that the stress which has caused them was what we may term quaquaversal—that is to say, it has acted in several directions around the greater part of the hori- zontal circle. This behavior of the crustal stress is quite different from that which we find exhibited in normal mountains; there, as before remarked, the relief has been obtained by the formation of ridges and furrows, the axes of which are nearly parallel to the same great circle. Although the amount of this parallelism has usually been much exaggerated, there can be no doubt as to its substantial existence. However, it seems unwarranted to suppose that the axial relation of the ridges is due to the existence of a strain acting in but one direction. All that is required to produce the result is either a certain predominance in the value of the strain in a particular versant, or, what comes to the same thing, a greater tendency to yield along one set of lines. Instances of this may frequently be seen in the wrinkling of veneers or in sidewalks which have been covered with some plastic materials. With a simple device the cream on a pan of milk may be made to show the effects of the same general principle, where the giving way takes place rectilinearly, though the difference in pressure in the several axes of the circle is but small. Moreover, even in the most nearly parallel mountains, there are generally to be found cross folds which show very clearly that the strain has not been uniaxial. The foregoing considerations lead us to infer that the diversity of axes in the elevations produced in the singular group of antecedent basin folds which we are considering has not been brought about by a class of strains differing as regards their distribution from those involved in the formation VARIATIONS OF SEA LEVEL. BO of ordimary mountains, but rather through the opportunity which these diversely shaped and irregularly disposed basins have afforded for the varied application of the stresses. As before noted, the evidence derived from the geological history of southeastern Massachusetts and the neighboring portions of the shore to the northward as far as the Gulf of St. Lawrence, and to the southward into the Carolinas, shows that while this coast line has been subjected to repeated and considerable variations of level, it manifests an equally clear tendency to return to about its original position. Beginning with the Cambrian time, we find reason to believe that this region was coastal at the outset of the Olenellus epoch. If the rocks of the Roxbury conglomerate be of the Potsdam period, the same was true at the last of the Cambrian stages. It is again the case in the Carboniferous, in the Trias, the lower Cretaceous, the middle Tertiary, and at the present day. Evidence found on the coast of Maine indicates that the coast in that part of the field was also near by in the Devonian period. ‘Thus, in eight or nine of the great periods, well spaced through recorded geological time, we find the coast of this dis- trict near to its present attitude. As the action of erosion during the periods of elevation, and the accidental burial beneath later deposits of portions of the strata, are likely to have obliterated much of the record, the point which we are endeavoring to make appears to be well affirmed. This point is of evident value in the present inquiry, for it serves to show a reason why extensive erosion valleys are characteristic of the Atlantic coast. In those phases of the coastal movement in which the land has been above the present level of the sea, there has been an opportunity for the formation of extensive valleys of erosion, which, from time to time, with the downsinking of the shore line as a whole and the downward warping, concomitant with the extensive deposition, have had a chance to take on their present peculiar character. Tn this connection it should be noted that the usual tendency of shore- line changes on the periphery of the continental fold is to return the coast after each considerable oscillation to somewhere near where it was before. Elsewhere, more than once, I have called attention to the facts that within the ordinary growth of the great corrugations on the earth’s surface the movements are normally those of downsinking of the ocean floors and uprising of the emerged portions of the continental mass, and that this MON XXXIII——3 34 GEOLOGY OF THE NARRAGANSETT BASIN. movement is essentially like the rotation of the lever about the neutral or fulerum point, which is ordinarily near the shore line. On the doctrine of probability, it is more likely to fall at the contact of land and sea than at any other point in the length of the rotating area. Hf the land advances from the ancient shore, the natural result is an increase in the amount of erosion and consequently of deposition off the given coast line. This, in turn, as an effeet of the loading, tends more sharply to depress the region next the coast, and so, in time, to a return of the shore toward its original position. If, on the other hand, the sea invades the land, considerably narrowing the field of erosion, the supply of sediments is checked and the element of accumulating weight which makes against the uprising is proportionately lessened, with the resulting tendency of the district to ascend in the next adjustment of the crustal stresses which are involved in continental growth. So far as lam aware, the mountainous elevations which have been formed along the Atlantic coast appear to have been the result of stresses which have acted in a somewhat continuous manner from the Cambrian to near the present day. The dislocations seem to have occurred in these basins as early as the first-named time, and in the basin of Marthas Vine. yard they operated perhaps until the first stages of the last Glacial epoch. It is true that the evidence as to the distinct basin-like position in which the rocks of Marthas Vineyard lie is not very clear, for the reason that the eastern wall, if such wall existed, is now below the level of the sea; but the mountain-building nature of the disturbances appears to be unquestion- able, the original folds having had a geological height of several hundred feet, though, owing to the soft nature of the strata. they have now been reduced to near their base-levels. It is anotable fact that in these erosion-basin mountains of the Atlantic coast there is a manifest tendency of the streams to return again and again to somewhere near the paths from which they have been displaced by the subsidence of the areas beneath the sea or by the corrugation of the beds which were formed during these periods of depression. ‘Thus in the case of the basins along the coast of Maine, those of Boston, the Connecticut, and the set about the Chesapeake, streams answering to the original agents of erosion now occupy thew ancient sites. It is evident that m this particular, as in many other features, the dislocation areas we are consider- ORIGIN OF SEDIMENTS. BY) ing ditter from those of normal mountains. In the last-named group, as has been often remarked, the streams very generally come to occupy the geological highlands—the crests of the anticlines. The reason of the departure from the general rule in these antecedent basin mountains is that in them the rim is of hard rock, while the central portion of the area con- tains softer materials. It should furthermore be noted that the downsinkings which lowered these valleys, and thus afforded the opportunity for deposition, were not generally so extensive as to induce the formation of normal marine deposits. After the beginning of the Carboniferous, indeed, it may be doubted whether the submergence beneath the level of the sea was, until Cretaceous times, ever great enough to mantle far over the surface of the country. Apart from the local downsinkings, I see no reason to believe that the shore within this time has swayed downward or upward more than a few hundred feet. So far as the examination has been carried, the seat of origin of the detrital materials contained in the Narragansett Basin is tolerably well explained. The granitic, trappean, schistose, and other rocks represented in the conglomerates, with a single exception, may be paralleled from deposits the like of which are known within a few miles of the margin of the basin. The exception—a most notable one—is in the case of certain quartzite pebbles, sometimes containing an abundance of ill-preserved brachiopods. These quartzites are all fine grained, hardened, but not greatly metamorphosed, and of a hue varying from blue to white. The age of the material, as determined by Walcott, is that of the Potsdam sandstone. Pebbles of these quartzites plentifully occur im the upper conglomerates of the Narragansett series, as is elsewhere noted in this memoir. They are, however, best known trom their occurrence in the drift deposits, where their. presence is doubtless to be explained by the breaking up of the Carbon- iferous beds in which they formerly lay. On the northern shore of Marthas Vineyard they can readily be gathered to the number of many thousands, and on Cape Cod they occur less plentifully as far east as Highland Light. As the pebbles, so far as observed, are always small, never exceed- ing about a foot in diameter, and as they are always rounded in a sub- spherical form, it seems clear that none of them have been brought into 36 GEOLOGY OF THE NARRAGANSETT BASIN. their present position from the original strata by the action of the last ice period. Forming, as they do, a considerable part of the mass of conglom- erates in the Narragansett Basin, it is clear that they were derived from an extensive field. Their condition indicates that they were imported from that field by torrent action. Although it is possible that these quartzite deposits originally lay over the country to the westward of the Narragansett Basin, the failure of the beds to appear round the periphery of that area leads to the supposition that the district whence they were derived lay to the eastward of the trough, perhaps beneath the region now covered by the sea This supposition receives some warrant from the fact that these peb- bles are most abundant in the eastern portion of the basin, while they seem to be almost lacking in the western part. The existence of these pebbles well toward the extremity of Cape Cod appears to indicate the occurrence of similar deposits beneath the waters of Massachusetts Bay. For further details concerning the origin of these quartzite pebbles, see Part II, by Mr. Woodworth. AGE OF THE CARBONIFEROUS ROCKS OF THE BASIN. The evidence goes to show that from the earliest stages of the Pale- ozoic to the beginning of the era when the Carboniferous beds of this district began to be laid down the field was mainly, if not altogether, the seat of erosive actions. No remnants of the formations between the lower Cambrian and the Carboniferous have been found in folds which exist in the basement rocks of this part of the country. The fact that beds of Cambrian age have survived at several points in the Narragansett Basin im the region to the northward, while no deposits of the Silurian or Devonian horizons have been identified, leads to the supposition that the sediment- making conditions were not in existence at the time these beds might have been laid down. The researches of Lesquereux, a digest of which is given by Woodworth in Part H, make it eminently probable that the Carboniferous series of this field does not begin with the lower portion of the Coal Measures, but with the upper part of that section. Not only are the lower limestones and the Millstone grit lacking, but about half of the measures which normally contain a better coal in the district west of the central Appalachian axis are also lacking. It should be observed that the fossils which afforded the basis for SEPARATION FROM THE SEA. ont Lesquereux’s conclusions were obtained from beds which lie at 2,000 to 3,000 feet above the base of the Coal Measures as found in this basin, and that the beds whence his fossils were obtained do not extend nearer than 2,000 to 4,000 feet to the top of the highest remaining beds of Carboniferous age which are found in this area. It is of course possible that the lower portions of the section, the fossils of which have not yet been studied, may prove to belong to the lower Coal Measures, but the essential lithological similarity of the beds below the upper conglomerates makes this view improbable. So, too, the lack of paleontological evidence concerning the precise age of the upper conglomerates permits the suppo- sition that they may belong to the Permian period. ORIGINAL RELATION OF THE NARRAGANSETT BASIN TO THE SEA. It is noteworthy that no trace of marine fossils has been found in any portion of the Carboniferous section in this basin. Moreover, there are no limestone pebbles which would lead to the suspicion that beds of this origin had ever formed a part of the original sections. A few limy deposits which occur in the northwest portion of the area appear to be the results of infiltra- tion, and to be classable as veins. When we consider that the Carboniferous section of the West Appalachians exhibits evidence of frequent intrusions of the sea, the question arises how a basin having the stratigraphical profundity of that of Narragansett Bay could have been developed adjacent to the shore line without having, in its repeated subsidences, experienced marine invasion. At the present time the bottom of this basin lies several thousand feet below the plane of the ocean waters which penetrate it. ven before the mountain-building movements which have deformed the rocks began, it is probable that the basin had something like its present depth. The conditions of the basin, as above noted, lead to the conelusion that during the Carboniferous period it was continuously separated from the sea, and therefore had the character of a lake, or perhaps that of a broad river valley. As it was evidently the seat of very considerable drainage, the out- going water might have excluded, in a sufficiently effective way, the pene- tration of the oceanic waters, even though the plane of deposition was not much above the marine level. When, however, we consider how subject all coast lines appear always to have been to oscillations of level, it seems most reasonable to suppose that the basin lay always at a considerable 38 GEOLOGY OF THE NARRAGANSETT BASIN, height above the coast line, and most likely at some distance inland from it. These considerations serve to support the hypothesis, which is suggested by many other features of the Atlantic shore line of North America, that the shore line in later Paleozoic time lay farther east than it does at present. ORIGINAL DISTRIBUTION OF THE EAST APPALACHIAN COAL FIELD. The distribution of the Carboniferous strata with reference to the main axis of the Appalachian system affords some valuable information as to the movements and attitudes of the continent during the later stages of Paleo- zoic and the earlier stages of Mesozoic time. It is noteworthy that, while the Carboniferous of the West Appalachians exteuds to the southward until the beds pass beneath the Cretaceous and Tertiary deposits which le to the north of the Gulf of Mexico, rocks of that age are wanting along the Atlantic coast until we attain the latitude of northern Connecticut and southern Massachusetts. Thence to northern Newfoundland accumulations of this age occur, though in detached basis which were evidently formed as somewhat separate areas. The uniform absence of Carboniferous deposits, and indeed of the Paleozoic beds above the Silurian horizon, along the southern portion of the Atlantic coast line of the United States, clearly mdi- cates the long continuance of this part of the content in the emerged state, a state which appears to have continued in the southern section to Triassic time, and perhaps to the Newark division of that age. If Coal Measures strata had been deposited on this part of the Atlantic coast above the pres- ent sea level, it is hardly to be believed that considerable remnants would not have remained in the Dan River, Richmond, and other basins. The natural conclusion is that these beds were not laid down, but that the shore from the Hudson southward remained in the elevated state, and that in this field Carboniferous strata were not accumulated, while farther north the conditions so favored this work of deposition within the region about the mouth of the St. Lawrence that the sections of this stratigraphical division are on the average thicker than they are in the West Appalachian field. With the advent of the Triassic epoch the whole coast line appears to have been lowered, so that the beds of this age probably formed a more or less continuous sheet from South Carolina to Nova Scotia. In the Carboniferous downsinking of the eastern shore the conditions which brought about the formation of the Coal Measures do not seem to have extended as far south as the valley of the Connecticut. The pre- ATLANTIC COAST BASINS. 39 sumption that this trough is old, and that in the Carboniferous period, if it had been sutticiently low lying, it would have afforded a favorable field for the accumulation of strata, is supported by the fact that Helderberg strata are found within its bounds, and the absence of the later Paleozoic is fair proof that the trough was so placed that it remained subjected to erosion. In this connection it is interesting to note that the Triassic period does not appear to have introduced true marine conditions along this coast line. The fossils indicate that the beds were formed either m fresh-water lakes or in estuaries. So, too, the Carboniferous strata of the East Appalachian district contain only fresh-water fossils, notably lacking the thin beds containing marine fossils which in the West Appalachian district clearly indicate successive invasions of the sea. These facts are best explicable on the supposition that the Atlantic coast in this part of its history lay farther to the east than it does at present, and that all the beds from the beginning of the Carboniferous upward through the greater por- tion of the Triassic section were formed in basins so far separated from the sea that no marine life found access to them. The development of fresh-water basins on the Atlantic coast in the Car- boniferous period has perhaps its parallel on a larger scale in that curious formation of shallow lakes which occurred in Cretaceous time along the eastern border of the Cordilleras of North America, and which gave during the Mesozoic and a part of Tertiary time the nearly continuous fresh-water areas from Texas to the high North. Depressions of this nature appear to be of common occurrence along the bases of mountain ranges which have rec ‘ently been subjected to extensive movements. It seems possible, indeed, that they are due to counterthrust action, which tends to bear down the part of the earth immediately outside of the field of considerable elevation. Phenomena of this sort are traceable not only in this country, but around the margin of the Alps and other mountain districts which have been suffi- ciently well mapped to give indications of these old basins. On this suppo- sition we can account for the general tendency of the East Appalachian district to subside during the time when the neighboring ranges were under- going elevation. ‘The intensification of this subsidence at particular points and the consequent infolding of strata, which have thus been preserved from erosion, is to be explained through the ac ‘cumulation of thick deposits of unconsolidated rocks in preexisting erosion tr oughs. 40 GEOLOGY CF THE NARRAGANSETT BASIN. ANCIENT MARGIN OF THE BASIN. The original extension of the Carboniferous beds the remains of which are found in the Narragansett Basin can not be determined. The evidence goes to show that in the process of filling the trough the margin of the field in which the deposits were accumulated extended in a somewhat continuous manner in every direction, this extension being in a way coin- cident with the progressive subsidence of the area. ‘There must thus have been a succession of shore lines, each lying farther away from what is now the central portion of the field. Itis probable that the arkose deposits which are now found around a large part of the margin of the existing Carbon- iferous area were accumulated at no great distance from what was the shore line at the time they were formed; but the later shore, answering in age to the upper conglomerate, may have been some scores of miles beyond the present limits of the Carboniferous rocks, the materials beg brought in over the shelf of earlier-formed deposits. The fact before adverted to, that the fossil-bearing quartzite pebbles come from some unknown and possibly rather remote district, indicates the validity of this hypothesis. Although the Carboniferous section of this basin is thick, the fact that the conditions favored the formation of rapidly accumulating conglomerates of itself suggests that some portion of the sectron has been worn away The fact that no higher-lying beds than the Carboniferous exist in this por- tion of New England, although there is abundant evidence that a large amount of erosion has taken place since the time of the Coal Measures, is also evidence that a considerable thickness of stratified rocks must have disappeared from this field. The margin of these vanished formations must have been far beyond the limits of the Narragansett Basin. RELATIVE EROSION OF EAST AND WEST APPALACHIANS. It requires but a glance at the topography of the districts lying to the east and to the west of the ancient or mid-Appalachian field to show the observer that there has been a great difference in their erosional history. On the west we find the mountain folds on the whole well preserved as regards both their anticlinal and their synclinal elements, the average pres- ervation of the structural features being more perfect than that of any other equally well-known great mountains, except, it may be, portions of AGE OF DISLOCATIONS. 41 the Jura. In most cases the crests of the anticlines have been widely opened by erosive processes, and in some rare instances the destruction has advanced so far that the synclinal element in the foldings has come to lie farther above the neighboring drainage than the existing crests of the upfolds. Notwithstanding this excessive local downwearing which has here and there taken place, the West Appalachians have everywhere, except in their extreme southern part, retained a striking topographical relief. It is indeed easy to see, even in the most ruined part of these great geological edifices, the plan of the structure and the general features of their archi- tecture. It is quite otherwise with the related elevations of the Atlantic coast. As before noted, the Kast Appalachians have, in their topographical expression, scarcely a semblance of the structure of the West Appalachians. In fact, their lack of relief has to this day hidden from geologists their real importance as orogenic phenomena. Between Georgia and the Bay of Fundy none of these mountains have any distinet topographical relief. Here and there the crystalline rock which were formed under their anticlines, or the massive outbreaks of igneous rocks which took place during the folding, remain as considerable hills, or in the case of the Mount Desert elevations they may attain the height of 1,000 feet or more; but in the Narragansett Basin, although the folds cer- tainly have a geological relief of not less than 10,000 feet, the actual differ- ences in altitude from the depth of the present water channels to the highest elevations does not exceed 500 feet. If these mountains of the East Appalachians had been no more worn down than the Alleghenies, they would afford the most majestic elevations in the eastern part of the continent, instead of having no distinct value in respect of topographical relief. It might at first be supposed that the age of these eastern reliefs is ereater than that of the western dislocations; the evidence, however, points to the conclusion that, while some part of the dislocations may be due to accidents date from post-Carboniferous times, and are probably to be assigned to the ageof the Trias or the Jura. The disturbances which have contorted the Cretaceous or Tertiary rocks of Marthas Vineyard clearly indicate that the orogenic forces have acted along the Atlantic coast with much energy down to very modern time. ‘To what, then, can we attribute the very great differences in the relief of these two mountain-built districts? 4? GEOLOGY OF THE NARRAGANSETT? BASIN, The modern school of topographical geologists is disposed to explain such differences as those which we are considering by the supposition that the region of less relief—the eastern—has been long base-leveled, without the refreshment of its relief which is induced by a subsequent process of reelevation; while the western district, having been once, or perhaps more than once, worn down to near the ultimate erosion plane, was lifted again to a height which permitted the machinery of its torrents to sculpture new reliefs. In favor of this supposition there is the fact that the summit levels of many peaks in the West Appalachians are so nearly in one plane that it is not unreasonable to suppose, as a ‘working hypothesis, that the valleys have worn down from an ancient base-level. To this suggestion it may be answered that, so far as the evidence goes, there is reason to believe that the eastern shore has shared in these upward movements. ‘The Berkshire Hiils show, by the coincident levels of their summits, as distinct a trace of base-level as do the Alleghenies. Moreover, in the immediate vicinity of the Narragansett Basin the broad ridges of the Worcester axis carry its levels to about 1,000 feet. Yet it is plain that this set of folds owes its origin to the same movements that developed those of the Bay district. In a word, even if we allow that uplift after base-leveling in the one case and lack of the upward movement in the other might account for the very great difference in conditions, we have not the means to verify the hypothesis; it therefore has no apparent value to us in interpreting this field. Although I regard the considerations which are commonly included under the title of “base-leveling” as one of the most important contributions to physiographical geology, it seems to me that we must guard against the danger of inferring too much concerning the existence of ancient leveling of the land down to near the plane of the sea from the seeming accords i the altitudes of mountain summits. It is easy to see that this accord is only of a very general nature, it being necessary in the classification to allow a range of elevation amounting to several hundred feet. It may well be that, beginning with the utmost diversity which could have existed in the heights of the Alleghenies, the process of downwearing might have brought about as near an approach to uniformity of height as actually exists in the peaks of that range. So long as the rocks are of like hardness and the folds of like size, the tendency would be to keep the downwearing crests at some- where near the same level. CONTINENTAL SHELF. 43 Another reason tor the disappearance of the topographical relief of the Kast Appalachians can be found in the marine erosion to which they have been subjected. As before remarked, it is evident that the Atlantic coast of this continent has for a very long time been in about its present relations to the sea. It is characteristically an old shore, and has the marks of age in the broad continental shelf which fringes it on the east and in the wide belt of lowlands which lies to the landward of the coast line. These two features seem to be closely related to each other; the submarine shelf probably represents in good part the accumulations of débris which has been worn from the bench which the sea has cut into the land. Because it is covered by the sea, we can determine but little of the continental shelf, except by inference from what we reasonably take to be an emerged part of its mass as it appears in the structure of the great southern coastal plain, that plain land being evidently composed of conti- nental waste in part removed by marine action, together with the débris of organic forms; but of the bench we may know much, for the greater part of it is above the sea level. If the student would appreciate the importance of this seaboard bench on the Atlantic coast of the United States, he should study the section from the great Appalachian Valley to the sea. Probably the most instructive section is from the region of the upper Shenandoah to the region about Fort Monroe, in Virginia. It is readily noted that the crystalline rocks on the western side of the Blue Ridge rise steeply from the broad vale which is occupied by the Cambrian beds. On this side of the ridge there is no trace of benching; the mountain sides show the ordinary torrent slopes. On the eastern side of the ridge, however, there lies the extensive rolling country commonly known as the “ Piedmont Plateau,” which has been recognized as a peculiar feature in the section from New Jersey to Georgia ever since the country was occupied by the uropeans. This region has peculiarities of soil and of surface aspect which are due to the fact that it is to a great extent underlain by crystalline or metamorphosed rocks essentially like the complex which makes the higher country of the Blue Ridge. When the rocks exhibit bedding, the attitudes of the strata indicate highly compressed mountain folds. The topography of the district shows much torrent cutting on the surface of a sloping bench which declined toward the sea at the rate of 10 or 20 feet to the mile, the upper or northern margin of this bench passing rather suddenly into the steep slopes of the mountain ranges. 44 GEOLOGY OF THE NARRAGANSETT BASIN. The conditions of the surface are in the main as shown in PI. J, with the exception that occasional outliers of high land are found over the Piedmont district. These outliers have the general aspect of ancient islands, the bases of which have of late been elevated above the sea level. Perhaps the best instance of these structures is afforded by Ning Mountain, North Carolina, which, as has recently been shown by the studies of Prof. Collier Cobb, of the University of North Carolina, is an insular mass which has by elevation been embodied in the area of the emerged continent. It should be said that this bench, with local variations, extends along the Atlantic coast of the continent as far north as the St. Lawrence district, but that the ancient islands are nowhere so well shown as in the Carolinian section. The foregoing statements will make plain the working hypothesis as to the erosion of the East Appalachian reliefs. We see that these moun- tains lie in the realm of the marine bench, that border land of the continent, where the repeated up and down goings of the sea bring the machinery of the surf and the other erosive agents of the coast line—the frost, the tides, and the winds—to bear in succession on every part of the surface. In recent years there has been a disposition to deny to marine action any considerable effect on the topography of a country. This limited view is a natural recoil from the old notion that the sea is the principal agent in land carving. From overestimating the value of a natural agent, the inevitable step is toward an underreckoning, which seems in this case to have gone altogether too far. A part of the misestimation as to the ero- sional value of the shore agents is due to the study of coastal processes in what we may term adjusted shore lines, such as are to be found where the sea has acted for a long time on a coast where the lands have not altered in their position with reference to the sea. In such conditions the sea, by a complicated system of actions, builds a series of obstructions in the way of shallows and beaches, which serve to bar the land from its assault, and which often cause the energy of the waves and tide to be expended in such wise as little if at all to erode the land. Wherever we are able to study the action of the sea where the land is rapidly oscillating, we note at once the great increase in the effectiveness of the ocean’s work. Thus, on the coast of EFFECTS OF CHANGES OF LEVEL. 45 New Jersey, where the subsidence is at the rate of perhaps 2 feet in a cen- tury, the formation of the usual sand barrier beaches is prevented for a considerable section, with the result that the sea, save for the interference of man, works back into the cliffs at the rate of several feet in a year. While a process of subsidence is in general favorable to marine erosion, that of elevation is probably yet more advantageous to the wave and cur- rent work: and this for the following reasons. When the land sinks, the débris due to the surf remains in the possession of the sea and may be used to build barrier beaches at a higher level. Off the coast of North Carolina, where there is also a subsidence movement, because the amount of sand is large, the beaches are still effective walls against the sea. When the land rises, however, the beach material is constantly left behind in the elevated coast lines, and at each successive zone of attack the sea assails an unmasked shore. At present we appear to be in a period where the land oscillations are relatively very slight; we therefore are in a posi- tion where we would naturally underestimate the true measure of marine erosion. Still, taken in a large way, we can easily see that the coastal erosion is by far the most effective at the times, which we know to be fre- quent, when the shore is moving upward or downward. This shoreward- sloping bench may be taken as the result of the two main varieties of land wearing—that due to the natural work of the rainfall, and that due mainly to the stroke of the waves as they break upon the coast. In the equation which determines the slope of the coastal bench, we have to reckon the effect of many agents and conditions. Among these, the successive changes of the base-level—i. e., the plane of the sea—are obviously of great importance. As the surface of the bench gains in height, the capacity of the marine agents become relatively diminished, for the reason that the marine cliff grows higher and the waves have more deportation to effect for each unit of the extension of the scarf into the land. On the other hand, with the gain in height there comes a proportional gain in the wearing power of the rain water, the capacity of which to do wearing work is directly related to the height above the sea at which it comes upon the land. Although the conditions which are now found on the Atlantic coast of the country are clearly less favorable to erosion than the average, it 1s evi- dent to the attentive observer that the amount of marine erosion which is now done along the coast from Cape Hatteras to Canada equals if it 46 GEOLOGY OF THE NARRAGANSETT? BASIN. does not exceed in volume that which is accomplished by all the rivers which empty into the sea along this part of the shore. We may say, indeed, that the evidence, when fairly cousidered, leads us to the conclusion that the destruction of the reliefs in the Atlantic coast mountains—the East Appalachians, as we have termed them—has been in a large measure due to the long-continued action of the sea on the zone in which they lie. In the case of the Narragansett Basin it seems impossible to account _ for the destruction of the original reliefs by the action of water on its way to the sea. If we take account of the existing water-filled troughs, the arms of the sea, and the rivers, we find a plain cut by relatively wide and. shal- low canyons, which are now to a great extent filled with drift. This plaim is underlain by rocks of very diverse hardness, so that if its surface were due to the result of the downwearing action of streams it should be most irregularly carved, in place of having that shorn-off aspect which the horizontally delivered stroke of the waves produces. Therefore we may conclude that the difference between the reliefs of the Kast and the West Appalachians requires us to consider the benching action of the sea along with the base-leveling process effected by rivers. Undoubtedly this latter base- leveling action has to be reckoned, but only as one, possibly the least, important element im the action. It may be noted, in order to complete this interesting story, that the greater part of the West Appalachians was fully protected against the action of the Atlantic by the rampart of the Blue Ridge. It is a corroboration of the hypothesis that at the southern end of the West Appalachians, where these mountains were exposed to the action of the waves of the Gulf of Mexico probably at least until the end of the Cretaceous or the middle of the Tertiary period, the mountains show a measure of erosive action hardly less than that which is exhibited by the worn-down ridges of the Atlantic seaboard Some further consideration of the question as to the wearing down of the rocks of this basin will be found in the next chapter, on the glacial history of the field. RECENT CHANGES OF LEVEL. It may be well in this connection to note the facts concerning the recent changes of level in the Narragansett Basin. As elsewhere remarked, the evidence goes to show that the amount of glacial wearing, or at least EFFECTS OF WAVE ACTION. 47 that of the last ice epoch, on this field was limited. We may therefore assume, what is inferred from other evidence, that the drainage of the district is substantially the same as it was before the last advent of the glaciers. The drainage consists of sundry deep channels, the arms of Narragansett Bay and their continuations in the narrowed rivers. To explain these stream beds, we must assume that the surface of the country was considerably higher during the preglacial time than it is at the present day. If, as is probably the case, the central part of the bottom of Nar- ragansett Bay is filled in with mud to the depth of 100 feet or more, as is the case with other channels of like character on this part of the coast, then the recent subsidence may exceed 300 feet. A like process of reason- ing applied to other parts of the shore between the Delaware and the St. Lawrence leads to approximately the same conclusion as to the amount in which the sea has gained on the land. It should be said, however, that this change in the position of the shore may be due to an alteration in the level of the sea itself quite as well as to the lowering of the land in this part of the shore; in fact, the extent of this modern invasion of the iand by the sea along nearly all the shores of the continents raises the presumption that the action may have been due to a vast movement of the floor in some part of the ocean realm. GENERAL STATEMENT CONCERNING BASE-LEVELING. What has been said in the preceding pages concerning the relations of marine and land denudation makes it desirable to assemble the considerations which bear upon this problem. There can be no question as to the importance of the base-leveling theory, which assigns to the atmospheric agents of erosion the downwearing of the land masses. It should be noted, however, that the marine agents— the cutting action of the waves and the marine currents dependent on wind and tidal work—haye in their appropriate place a certain amount of influ- ence. It should also be noted that as the land is worn down toward the level of the sea the efficiency of the atmospheric forces in the work of further reduction continually diminishes, because of the lessened fall of the streams and from the tendency of the surtace to become deeply covered with a protecting detrital envelope. In the low levels of the land, where the aerial agents become less 48 GEOLOGY OF THE NARRAGANSETT BASIN. effective, we may always expect to find some effect arising from the repeated visitations of the sea brought about by the almost continual oscillations in the height of the land. The measure of this marine work is commonly the greater the nearer we attain to the average level about which the sea has oscillated for a considerable time. Thus marine action comes im to sup- plement that of the atmosphere. Along the coast of New England, and particularly in the district con- sidered in this report, within the limits of the recent oscillations of marine level, we find at many points evidence that the sea at higher stations than now worked to remove the coating of detritus and to expose large areas of the surface to the process of decay, which rapidly tends to break up the rocks. This part of the marine work, in favoring erosion, is perhaps of as much consequence as that due to the direct cutting action of the sea. It may be remarked that the frequent invasions of the sea, by producing plains of detrital material, such as those which exist in the southern part of the United States, tend also to reduce the surface of the land to an approximately level form. Thus the evidence goes to show that beneath the southern plain the contour of the ancient rocks is irregular, they having been mantled over by a thick coating of débris accumulated along the continental shelf. We therefore see that the ocean tends in two diverse ways to bring about coastal plains—first, by aiding in wearing down origi- nally irregular surfaces to a level attitude; and secondly, by constructing detrital plains over those surfaces which in part have thus been brought to a nearly horizontal attitude. As for the oscillations of the land which serve to bring the mill of the surf at various levels over its surface, it may be said that since the Carbon- iferous period there is evidence of many such swingings, which have brought the plane of the sea from a few score to several hundred feet above its present position on the Atlantic base of the continent. The evidence to the same effect from other regions is so extensive that it may be called a world-wide phenomenon.. It may safely be assumed that coast lines are normally instable, and this through a range of several hundred feet. As to the amount of cutting which can be effected by the sea in pro- portion to that which may be accomplished by the descent of waters from a high level to the shore line, the facts are not yet sufficiently ascertained to permit any definite statement. It may be said, however, that where the exposure is such that the waves may assault the shore with considerable SUCCESSIONS OF DEPOSITION. 49 energy, especially where the tides are high, the erosion, even ina brief period of geological time, is often very great. Thus on the coast of Yorkshire, north and south of Whitby, the marine cliffs, apparently formed in the brief period during which the sea along that coast has had its present attitude, have an average height of several hundred feet, and the platform which marks the lower range of wave action extends on the average a mile or more from the shore. The prism of rock removed by this cutting is in mass greater than we can well assume to have been eroded from the land dur- ing the same period for the distance of 20 or 80 miles from the coast line. Along the shore of New England, though the coast generally lies against rocks of more than usual hardness, the benching action of the sea is almost always noticeable. In the few thousand years during which this coast line has remained at its present attitude, the amount of erosion has apparently been many times as great as over any equally extensive interior portion of the field subject to the action of atmospheric agents. Considering only the hard rocks, especially those of the coast of Maine, I am of the opinion that the atmospheric erosion accomplished in New England since the Glacial period has not been so great as that effected along the shore belt in the much shorter time which has elapsed since those coasts began to be assaulted by the sea. It is to be observed that, in all estimates as to the relative value of marine and atmospheric erosion, account must be taken of the dissolving action of the land waters, which is always wanting in the case of the sea. Although the interior erosion of New England is now exceedingly small, the solutional decay is gradually, indeed it may be said somewhat rapidly, advancing in certain portions of the glacial deposits, so that the time will come when they may pass off with greater rapidity. Making allowance for this and for other evident qualifications as to the relative value of marine and interior erosion, it may still be said that the former agent has a certain and important, though much neglected, influence in determining the shape of the lower-lying portions of the land mass. CYCLES OF DEPOSITION. Considerations as to the succession of phenomena of deposition which were brought into view by the writings of the late Prof. John S. Newberry and others, appear to receive no support from the successions of strata in MON XXXIII——4 50, GEOLOGY OF THE NARRAGANSETT BASIN. the Narragansett Basin. The first stage of deposition in this field, when the formation of the Carboniferous section began, is marked by the occur- rence of fragmental beds, mainly arkoses. Where the succession is well displayed, these arkoses are followed by conglomerates of no great magni- tude. Succeeding these with tolerable uniformity comes a section of several thousand feet where the deposits are prevailingly rather fine grained. In the upper half of the section there is a return to conglomerate-making conditions. This return appears to have been made rather suddenly. At first sight it seems reasonable to suppose that the succession of events, as indicated in a general way by the section, gave (1) a period in which the shore line was everywhere near to the margin of the present basin, permitting the formation of arkose; (2) a period when a continued depression kept the shore line always at a distance, resulting in the fine- erained beds; and (3) a reelevation, which, by pushing the shores toward the center of the field, led to the ready importation of coarse débris. It is evident that there are many circumstances which serve to qualify the interpretation which can be made as to this and other cycles of deposition. Manifestly the intensity of erosion, as well as of the transportation of detritus worn from the land, depends in large measure upon the ratio of the rainfall at different times. As this ratio doubtless varies in different periods, or even in different parts of the same period, the effect may be to produce ereat alterations in the character of sediments brought to any particular field. Moreover, along the coast line, when it is in a static condition, there is an obvious tendency to produce a shelf, which, advancing from the shores of the basin, may afford a slope over which, in time, coarse sediments may be transported to a distance from the shore to which they could not at first have attained. On these and other accounts it does not seem profitable to attempt any conclusions based upon the succession of beds in this area. ARKOSE DEPOSITS OF THE BASIN. As the interpretation of much of the history of the Narragansett Basin depends on the view that is taken of the arkose deposits which abundantly occur at various points around its margin, and are, indeed, a characteristic feature of that rim, it will be necessary to consider the significance of these accumulations. Geologists who have had to deal with arkose deposits have generally accepted the conclusion that they indicate the accumulation of detrital FORMATION OF ARKOSES. 51 materials derived from crystalline rocks which have been subjected to much deeay in place, so that they lost their original cohesion before they were subjected to transportation and were accumulated in their present situations. The essential characteristic of such deposits is that they contain considerable quantities of crystalline materials in which the fragments have not been reduced to sand, but retain, in good part at least, their original form. In other words, the presence of arkose beds means an antecedent decay in crystalline rocks, a decay taking place in such a manner as to loosen the crystals from their attachments without going far enough to disintegrate the bits. This action has been followed by the wearing away of the softened mass and the more or less complete rearrangement of the materials. In the present state of the study of arkose beds, pains has not been taken to discriminate the materials into the two groups into which they may naturally be divided. In certain cases, after the process of decay has broken up the texture of the crystalline rock, and perhaps removed much of its materials in the state of solution, the deposit remains essentially in its original place, where it may be covered by subsequently accumulated deposits. Even though recementation of the crystals takes place, the accumulation will have more or less of the character to which we gave the name of arkose. For convenience, we may class this group as unremoved arkose. Although the conditions which favor the formation of unremoyed arkoses must be of infrequent occurrence, instances of the kind are to be observed in certain parts of New England, where the preglacial decay reduced considerable quantities of the crystalline rocks to a disintegrated state, and where the beds thus softened were not removed by the glacial wearing, but remain to the present day covered by sheets of stratified or unstratified drift. The normal or transported arkoses can, in all cases, be discriminated from those which have remained in place, by the evidences of water action afforded by more or less obyious stratification. The most characteristic and readily interpretable deposits of arkose exhibited within the limits of the Narragansett Basin, indeed one of the most important accumulations of this nature ever described, occurs at Steep Brook, the station just north of Fall River, Massachusetts. At this point, lying against the granitic rocks which form the western margin of the basin, 52 GEOLOGY OF THE NARRAGANSETT BASIN. is a section of what at first sight appears to be a mass of granite which has decayed in place. This seemed to be the view which was enforced by the observed facts when these beds were first seen by me, about twenty-five years ago, and they had just been opened by prospectors who were led by a small outcrop on the brook to seek for fire clays. Further exploration, however, soon disclosed the fact that the mass exhibited traces of stratifica- tion such as were not to be found in the neighboring unchanged granite. A close study of the obscure divisional plane brought to light the existence in them of many well-preserved specimens of plants which belong to the Carboniferous time. This evidence indicates that the deposit was formed during the period of the Coal Measures. The considerable thickness of this section makes it clear that the conditions which led to its formation continued fora long time. ‘These conditions were substantially as follows: There was a rapid importation of semidecayed granitic rock, such as would be afforded by the decomposition of the crystalline materials which are to be found immedi- ately to the east of the locality. The rateof this accumulation appears to have been so speedy that there was no chance for a true soil layer to be formed on the growing beds. The plant remains which occur were evidently not grown on the sites they now occupy, but were fragments swept into their positions from a distance. It appears likely that they had been to a greater or less degree inclosed in ordinary ferruginous concretions before this transportation. The interpretation of the conditions at Steep Brook during the time when the forces which led to the deposition of the arkose were in action seems, in a general way at least, to be not at all difficult. It is evident that in the time preceding the deposition of the portion of the Carboniferous strata on which the arkoses lie, the portion of the continent about the Narra- gansett Basin had been long exposed to atmospheric decay without having been subjected to the conditions which would remove the decomposed material as rapidly as it was brought into the disintegrated form. Judging by the conditions which have affected the fields that now afford or that might produce the arkose deposits, we may assume that these levels of the Coal Measures time had long been the seat of a considerable rainfall and had maintained a coating of vegetation, such being the antecedent condi- tions of any decomposition which would prepare the way for arkoses. After the development of a sufficient depth of this rock decay, we have to DISTRIBUTION OF ARKOSES. 53 suppose that conditions favoring the rapid erosion of the decayed material were established. These conditions may have been brought about in any one of several ways: The region may have been subjected to glacial action; the rainfall of the area may have been increased in such a measure that the streams were made competent to waste the surface; or the area may have been exposed to wave action, either by being lowered beneath the level of the sea or by becoming the seat of a lake. The hypothesis of glacial action at the time these arkoses were formed does not, at first sight, seem to be supported by the evidence which is derived from the presence of well-preserved vegetable remains in the beds; but, as remarked in the preceding paragraph, these remains seem not to have been deposited in a fresh state in the growing accumulation, but to have been washed from some antecedently formed but practically contemporaneous deposit into the positions which they now occupy. Therefore the existence of ice wearing in this district at the arkose-building time does not seem improbable. We shall hereafter note that there is other evidence of a more positive nature going to show the existence of glacial conditions in this gravel period in the district about the Narragansett Basin. As a whole, the distribution of the arkose deposits of the Carboniferous time around the margins of the Narragansett Basin seems most easily to be explained by the supposition that streams of a swiftly flowing nature formed torrent cones when they debouched into a fresh-water lake which occupied almost the whole area now covered by the coal-bearing rocks of the district. That the deposits are in general those of torrent cones or deltas appears to be shown by their irregular distribution. In all cases where they have been observed they occur in rather detached patches, like accumulations which have no great extension in the direction of the ancient shore line. This seems to exclude the supposition that the deposits were formed in the manner of ordinary shore accumulations, where the débris is transported from a neighboring coast escarpment. There are no observations on record concerning arkoses now in process of formation, though such may be accumulating in many parts of the world. It is therefore not possible to ascertain with certainty the distance to which the angular crystalline débris of granitic rocks can be conveyed by stream action without losing the peculiar features which separate it from the ordinary products of the erosive forces which have acted on much 54 GEOLOGY OF THE NARRAGANSETT BASIN. decayed rocks. It happens that on the island of Marthas Vineyard there are extensive deposits of arkose formed during the Tertiary period, which appears to indicate that materials of this nature may be transported for considerable distances. The deposits at Gay Head contain very thick beds of arkose, probably brought from the granitic area lying to the northwest of the locality. It is difficult to conceive that the supply of the detritus could have been brought from less than two score miles away from the locality in question. It is of course possible that these Tertiary arkoses were derived from some granitic area near the place where they le—an area which by local subsidence or excessive erosion has in modern times been brought below the level of the sea; but the evidence in these cases is clearly against this hypothesis and in favor of the assumption that the little-rounded crystals from the granitic sources have been conveyed for forty or more miles. Therefore, while the Carboniferous arkoses afford clear evidence that they were deposited along the shores of a basin, no very clear evidence as to the field of their derivation can be obtained from the conditions of the beds. The arkose deposits of the Narragansett Basin are found in both groups of deposits which have been observed in the field, the Cambrian and the Carboniferous. In the former the evidence is limited to the region about Attleboro, that being the only portion of the basim where the Cam- brian strata are clearly recognizable. The Carboniferous arkoses are much more extensively distributed. They may indeed be said to occur as a characteristic feature in the margin of the basin, serving to show that, in a general way at least, the trough existed with something like its present horizontal limits as early as the time of the Coal Measures. At no other point are the evidences as to the conditions under which the deposits were laid down so clear, or at least so well ascertained, as at Steep Brook, but at all points the facts show that the materials composing the beds have been transported from a distance, and so far as determined the carriage has been from the sides of the basin toward its central part. It is important to note that the arkose deposits of this district appear to have been the first of a series of erosional phenomena leading in the end to the formation of extensive conglomerates. The stages are, first, the arkose material, or the waste of rocks decayed in place; next, the clays and sands, which may be regarded as the product of ordinary erosion, when EFFECTS OF RAINFALL ON ROCK DECAY, 55 the abrasive forces keep pace with the agents of decay; and finally, the conglomerates, formed when the abrasive actions go forward more rapidly than those which lead to the general softening of the rocks. RELATION OF ARKOSES TO EROSION. The above-mentioned facts concerning the succession of beds in the Narragansett Basin clearly point to the existence of what may be termed a cycle of erosion dependent on the relative rate at which the two diverse processes connected with the decay of the lands go forward. This equation, ina general way, seems to be as follows: Where the rainfall is so slight that a vegetal covering is not established in a country, the chemical assault on the rocks, which is due in the main to the CO, and other products which the decaying organic matter in the soil contributes to the ground water, is probably wanting. The result is that the erosive work, or that which oper- ates to remove the detritus in the form of visible sediment, though it may be very slight, is likely to be enough to keep the rocks which have been softened well cleared away. In such an arid country the rainfall is apt to be irregularly distributed, so that the torrent action is at times exceedingly strong. The result of this is that the valleys become encumbered with angular breccia-like débris, such as now exists in the valleys of the arid districts of the Cordilleras. An increase in the rainfall to the point where an ample mantle of vegetation is supplied, but short of the point where torrent action is made excessive, tends to produce a greater amount of decayed rock than can be cleared away. ‘The result is that the coating of what we may term the the nontransported arkose steadily increases in amount. The thicker this porous layer becomes the more the rate of the torrent action approaches uniformity, for the reason that the open structure of the decayed rock causes the cerroded zone to be an effective storehouse for the ground water, whence it is slowly yielded to the streams. With an increase in the rate of precipi- tation beyond the point where the water can be taken into the unoccupied detrital layer a critical point is soon reached where the mechanical erosion will rapidly increase and will gain on the process of interstitial decay. If the rate of mechanical wear much exceeds that of the decay, the result will be the deportation of solid waste in the form of pebbles, the process being marked in a geological way by the production of conglomerates. 56 GEOLOGY OF THE NARRAGANSETT BASIN. We thus see that in the erosional history of a region wherein the rain- fall varies from zero to the highest measure which we can expect, say over 100 inches per annum, we may look for a series of effects which will mark themselves in diverse classes of débris. So long as the decay keeps in general ahead of the abrasional work, the waste which goes forth through the streams is likely to be of a finely divided nature, giving rise to clayey slates as the natural product. If a stream yields abundant materials which would form arkose, it is because the erosion is gaining on the decay. If the work produces pebbles, the indication is that the mechanical erosion is so great that wearing by solution plays no important part in the process. In this connection it will be well to note yet further that the large production of pebbles within a short time can scarcely be accounted for except on the supposition that the abrasion has been brought about by the action of glacial ice. As the importance of this proposition has not been appreciated by those who have dealt with the problems afforded by con- elomerate deposits, we must note that there are but three ways in which waterworn pebbles can be made in sufficient quantities to afford materials for ordinary conglomerates. The first and practically the only effective means by which pebbles can be extensively made—i. e., in large amount per unit of surface over a large area—is by glacial action. Where the precipitation of a country goes off as an ice sheet, every portion of the rocks over which it flows, if the material be sufficiently hard, becomes a part of a vast bowlder factory—for such, in fact, is all the base on which the glacier rests. As the average thickness of the till covering in the glaciated district of this country is not less than 10 feet, and as the greater part of this till is bowl- ders, it is clear that ice in motion is specially adapted to forming such partly rounded bits of stone. The materials in our eskers show how successful the subglacial torrents, with their currents impelled by hydrostatic pressure, were in completing the rounding of pebbles which the ice began to shape. When the rainfall of a country goes to the sea in a fluid state, the tor- rent section of its river system, provided the rate of decay is swift, is likely to be the seat of the production of a considerable amount of pebbly mate- rial. Yet the share of the energy of the portion of the rain water which is then effectively applied to pebble making is but a small fraction of what is used when the same amount of precipitation goes to the sea in the form of a glacier. Moreover, the pebbles which are thus formed in ordinary tor- CONDITIONS OF PEBBLE MAKING. 57 rents are made in small quantities. No sooner does a torrent bed become loaded with this detritus than it ceases to be an effective factory of the rounded bits of stone. Furthermore, the pebbles which are formed in tor- rent beds rarely attain the sea or any position where they can be built into extended beds of conglomerate. Although I have inspected several thou- sand miles of seashore, much of it along mountainous coasts, I have never found a place where pebbles, such as are found in the conglomerates of the Narragansett Basin, from a stream of any size were entering the sea. It may, indeed, be regarded as rare for a stream to discharge into the ocean pebbles exceeding an inch in diameter. To do such work it would have to flow at a torrential rate at its very mouth, a condition which can be found in certain fresh-water lakes, but is rarely seen on the ocean coast line. The third means of pebble making may be seen along the seashore where the waves are attacking hard rock cliffs. In such conditions pebbles are formed, but they are rarely accumulated in large quantities; in general the fate of coast-made pebbles is to be worn out by the action of the forces which have shaped them. There are no agents whereby such marine pebbles in considerable quantities can be carried out for any distance from the shore. In rare cases ice forming along the coast is likely to inclose some portion of the shore débris; this shore ice may then drift out to sea and there deposit the load of pebbles which it has rafted. This action, though sufficient to strew the sea floor with shore-made stones, can not be looked to as a means of accumulating conglomerates. The above-mentioned considerations make it clear that it is not easy to account for the existence of widespread deposits of pebbles of consid- erable size accumulated in massive strata, which in the case of the beds of the Narragansett field contain perhaps more pebbles than exist on the beaches of the Atlantic coast or in all the torrent beds of the Appalachian Moun- tains. The easiest way, if not indeed the only way, to explain the forma- tion of extensive conglomerates is as follows: On the surface of a land area there must first be accumulated a considerable deposit of rock fragments, such as is normally gathered at the close of a glacial period, or such as occupies a region of high relief, scanty rainfall, and much frost work, after the manner of large areas in the Cordilleras and in other parts of the world where these conditions exist. If, now, such a fragment-strewn district is gradually lowered through the mill of a shore line either of the sea or of a 58 GEOLOGY OF THE NARRAGANSETT BASIN. considerable lake, the chance for the formation of normal conglomerates will be provided. The unorganized débris of the surface will be taken to pieces and recomposed into stratified beds, as is now being done with the glacial débris along the shores about the North Atlantic. In this formative process the pebbles are likely to be changed in shape and assorted as to size in a way which at once distinguishes the strata into which they are built from the beds of till or of residual breccia from. which the fragments were derived. There are certain tests of some value in distinguishing the conglom- erates made from rearranged glacial materials from those which owe their formation altogether to marine action. Pebbles made from fragments which have long been separated from the bed rock are generally, unless they be of quartz, much affected by decay; they contrast distinetly with the fresh quality of the ordinary glaciated pebbles. As I have observed in the southern part of this country, as well as in southern Europe, the detrital waste which comes into the streams is generally so penetrated by decay that it can not be made into pebbles; if perchance it holds together in the shaping, the eye at once separates the bit from those which are made from freshly riven stone. Where pebbles are made by wave action alone, it is a notable fact that they exhibit very little diversity im form; they are almost invariably sphe- roidal, and when they are accumulated in considerable numbers the litho- logical diversity of the material is small. Although glaciated pebbles are apt to be somewhat altered from their original subangular shapes as they pass through a surf line, many of them, as we may note along the New England coasts, will withstand a deal of hammering without losing the dis- tinct mark which the ice work impressed upon them. Moreover, taken col- lectively, whether in the original till or in the partly masked shore deposits, they commonly exhibit a large petrographical range of material. The facts which are available for the interpretation of conglomerates show that those of the Narragansett Basin are of what we may term secondary glacial origin. This is indicated by their frequent—indeed, we may say usual—sub- angular form, their petrographical variety, and the very small amount of decay which had affected the rock masses after they left their original bed- ding places and before they were deposited in the situations in which we now find them. EVIDENCE FROM CONGLOMERATES. 59 The hypothesis that the conglomerates of the Cambrian and Carbon- iferous as exhibited in this locality are the results of glacial action is sup- ported by the general distribution of such deposits in this and other countries. Massive conglomerates of great areal extent are distinctly more common in high than in low latitudes. With rare, and in most cases questionable, exceptions the deposits of this nature which can be traced horizontally for a great distance from north to south fade away as they approach the equator. As our study of conglomerates advances, more of the deposits are found to afford evidence as to the glacial origin of their pebbles. The great conglomerates at the base of the Carboniferous in India, which from their interstratified position appeared not to be open to the explanation which has been advanced in this writing, have recently afforded clear evidence to show that glaciation, possibly occurring at a time when the area was elevated to a great height above the sea, suffi- ciently accounts for the origin of the pebbles and bowlders which the beds contain. Although this is not the place for an extended discussion of the matter, it may be worth while to remark that a collation of the recent studies on conglomerated deposits clearly shows that we are fast approaching the point where beds of this nature will be taken as presumptive evidence of glacial action occurring at the time of their deposition, or perhaps imme- diately preceding it. RECORD VALUE OF CONGLOMERATES. In connection with these considerations relating to conglomerates, it may be well to note that deposits of this nature have another much neg- lected element of value to the geologist, in that they afford him an opportu- nity to ascertain many facts concerning the physical conditions of the region in which they occur at the time of their formation. Although the value of these indications is in good part self-evident, they have been so generally neglected that it is worth while to dwell upon the methods of using them and to illustrate them by a special study of the Narragansett field. If a conglomerate has not been subjected to metamorphic action sufficient to change the original character of its pebbles, these fragments may be taken as evidence concerning the state of the rocks whence they came at the time the pebbles were brought together. ‘This evidence, 60 GEOLOGY OF THE NARRAGANSETT BASIN. when examined, is seen to go very far, and in several directions. In the first place, the conglomerate may be taken as representing the beds which were exposed to erosion at the time it was formed. If the beds are of ancient and of known age, they may enable us to determine the former existence, in the field, of rocks which have since disappeared by erosion, been lowered beneath the sea level, or been covered over by other deposits. Thus, in the case of the Carboniferous conglomerates of the field under consideration, we find in the beds a very great number of quartzitic pebbles which contain fossils evidently of the Cambrian age. It is clear that the field occupied by the quartzites was extensive, for the fragments which appear to be of that group of rocks, though not always containing fossils, are about the most numerous of the components which make up some of the thickest layers of the Carboniferous conglomerates. A careful search of the rocks of eastern Massachusetts has failed to reveal the source of these fossil- bearing pebbles. Strata perhaps about the same age are found in various parts of eastern Massachusetts, but they are lithologically and in fossil con- tents very different from the strata which afforded the pebbles. While it is possible that the field whence the quartzite bits came has, by differential warping, been carried beneath the sea, it is rather improbable that such has been the case; it is more likely that the rocks in question lay on the margin of the basin, whence by erosion they have disappeared. It is a noteworthy fact that the above-mentioned quartzite is the only rock of the many contained in the Carboniferous conglomerates which has disappeared from this part of the country since these beds were formed. There are, it is true, certain uncharacteristic sandstone pebbles which can not clearly be identified with anything now in or about the basin, but these are not numerous. The impression left by the study of the Coal Measures pebbles is that the general character of the rocks exposed at the surface in this field in Carboniferous time was substantially the same as that of the rocks remaining at the present time. ‘This view is justified by a comparison of the materials contained in the ancient and the modern aggre- gations of glacial waste. Taking pains to exclude from the waste of the last Glacial period the pebbles which have been worn from the basin rocks of this field, the observer is at once struck with the likeness of the two assemblages, a likeness which shows us that the erosive agents found, with the exception of the above-noted quartzites, much the same rocks open to TIME OF METAMORPHISM. 61 their assaults in these two periods, which must have been separated by some millions of years. The field open to examination is much more limited in the case of the Jambrian conglomerates than in that of the Carboniferous pudding stones. Moreover, the pebbles contained in the beds have been subjected to more metamorphism. Nevertheless, the studies which have been made show that the rocks of the fundamental complex had attained about their present con- stitution before the beginning of the Olenellus epoch. These pebbles rep- resent the granites, gneisses, quartzites, etc., of the rocks which are found beneath the Cambrian beds, and show that the crystalline condition of these deposits was approximately the same as it is now. It is evident, however, that there were quartzites and other semimetamorphosed beds which afforded waste to erosion in the Olenellus epoch, beds which are not recognizable as in place in the district, and which perhaps, like those noted in connection with the Carboniferous, have disappeared from the district. It is neverthe- less clear that the greater part of the crystalline rocks of this district were already not only in their present mineralogical condition, acquired during a period when they had been deeply buried beneath other rocks, but had been stripped by the erosive forces of this ancient covering. It must not be supposed that the whole or even the greater part of the metamorphism which has taken place in this region had been accom- plished by Cambrian or even Carboniferous time. While in certain districts and with certain rocks this work seems to have been then completed, or nearly so, in other parts of the field the action continued at least until after the deposition of the Coal Measures strata. Thus the beds of the last- named series in the region about Worcester and in that about Wickford have been transformed to gneisses which, but for collateral evidence, could not be recognized as having been, in their original state, the associates of ordinary coals. It is evident that in this last-named field the process of metamorphism has gone on with exceeding irregularity, certain parts of the most ancient deposits—as, for instance, the fossiliferous strata of the Olenellus horizon—being not much altered beyond the induration common to all ancient flagey layers, while but a few miles away conglomerates have been so far converted into crystalline rocks that the original character of the beds has been almost completely lost. 62 GEOLOGY OF THE NARRAGANSETT BASIN, RED COLOR OF THE CAMBRIAN AND THE CARBONIFEROUS. The red hue of certain portions of the Cambrian as well as of the Carboniferous rocks affords a matter for inquiry. Though no solution of the problem has been attained, it may be well to note certain facts of possi- ble value to those who may hereafter attack the question. It is noteworthy that the red beds of both the above-mentioned series occur on the western and northern sides of the Narragansett Basin and in the trough of the Norfolk Basin. In both these sections the red beds are somewhat irregu- larly distributed, generally occurring between deposits which have no trace of the peculiar hue. In some cases, as noted by Mr. Woodworth, the red stratum may be but a few inches thick, lying between sandstones or arkoses of a whitish hue. This peculiarity of distribution is also very noticeable in deposits exhibited at Gay Head and elsewhere on Marthas Vineyard which, in Cretaceous and Tertiary time, were made under conditions some- what similar to those which existed in the earlier periods when the Narra- eansett deposits were formed. It seems likely that the red hue of stratified deposits is due to a variety of actions. In some instances, as along the present coast line of the region and about the mouth of the St. Lawrence, red beds may be formed by the disintegration of Triassic or other red sandstones and clays, the rearranged material retaining in large measure the hue of the rocks whence the débris came. In other instances, perhaps in the case of the Cambrian and possi- bly the Carboniferous of the Narragansett field, the red hue may be due to the fact that the beds thus colored originally contained a share of lime car- bonate. Downward-percolating waters containing iron oxide transformed these beds first into impure siderite, and further change served to bring the iron into the state of limonite. ‘The coloration thus brought about is fre- quently to be observed in the Devonian and Silurian rocks of the Appala- chian district, being particularly conspicuous in the iron-bearing members of the lower Devonian and upper Silurian strata of eastern Kentucky, as for instance in Bath County. In yet other instances the decay of erystal- line rocks containing a considerable share of iron may have provided the ferruginous material in a direct manner in the process of sedimentation. Some unpublished studies as to the amount of magnetic oxide in the drift covering which exists in this part of New England have shown me that the RED COLOR OF CAMBRIAN AND CARBONIFEROUS. 63 proportion of this material ranges from about one-half of one per cent to as much as five per cent by weight of the mass. As further oxidation of these crystals of magnetic iron goes on but slowly, the deposits in which they finally come to rest may contain a large share of the material which is to be, by further change, dissolved and distributed through the bed. Even where the ferruginous matter has been accumulated between the fragments of rock in the form of a thin vein or coating separating the bits, it may by a further process of change lose the iron in a greater or less measure and become a mere stain. Oat Ae I Tes, ILI Ie GLACIAL HISTORY OF THE NARRAGANSETT BASIN. The interpretable history of this basin, so far as it has depended on the action of ordinary streams and of the sea, has already been set forth. ‘This account of the effects of the solar energy which has been applied through the atmosphere needs to be supplemented by some consideration of the work which was done during the Glacial periods. The account which will here be given of the work will in the main be restricted to the phenomena that are in some measure peculiar to the field, for the reason that the surface geology of New England is to be the subject of a separate publication by the Geological Survey. Any full discussion of these matters in this memoir would therefore involve an undesirable repetition. We may first note that the deposits formed during the times repre- sented by the conglomerates of the Carboniferous series have a character which warrants the hypothesis that they are to a considerable extent the products of glacial action. The view that this age was a period of recurrent ice work has already been ably presented by the late Dr. James Croll. Here, as elsewhere along the Appalachian district, the supposition is sup- ported by an array of facts which deserve more attention than they have received. These facts, as they are exhibited in the country from Alabama to the St. Lawrence, will be briefly set forth. CARBONIFEROUS CONGLOMERATES. In the Southern States the conglomerates of the Carboniferous periods “are, with rare and unimportant exceptions, made up of pebbles of quartz, which, as has been noted by several observers, are evidently the remains of the undecayed veinstones that survived the decay which, in the pre- Carboniferous, as in the modern time, greatly affected the rocks that were exposed to the atmospheric agents. The great thickness of these quartz 64 CARBONIFEROUS CONGLOMERATES. 6D conglomerates, their wide distribution, as well as the general absence of fossil remains, are best explained on the supposition that the erosion took place in an ice time, being effected by the glaciers or by the currents of living water which coursed beneath them. In no way save by com- paring this ancient work with that now in progress in glaciated regions can we well account for the deposition of the Millstone grit of the Southern Appalachians. As we go northward from the valley of the Tennessee the Carbonifer- ous strata show an increasing amount of pebbly material which has been derived from the undecayed bed rocks. As elsewhere noted, these rocks indicate that there was at the beginning of the period a considerable thick- ness of decayed material, but before long the erosive agents had removed this friable mass, and thereafter the supply of pebbly matter, vast in amount, was obtained by the breaking up of bed rocks which show no evidence that they had been affected by superticial decay. As we go yet farther north, in the next field where the rocks of this age appear, i. e., in the region about the south shore of the St. Lawrence, the thickness of the conglomer- ate even exceeds that of the sections hereafter to be described in the north- erm part of the Narragansett Basin. In a word, the facts make it evident that the Carboniferous period of the eastern part of North America, like certain other periods, was one of exceedingly rapid alternations between the conditions which favored the development of marsh vegetation and others under which the accumulations of coarse sedimentary deposits went on with ereat rapidity. Although there are instances in which a torrent may accumulate a large detrital cone composed of bowlders and pebbles, I know of no geo- logical machinery now at work on the earth’s surtace, or which can reason- ably be supposed to have operated in the past, except glaciation, that is competent to produce such immense masses of coarse detritus as are contained in these conglomerates, or bring them into position where water action can effect their arrangement into beds. The area of the deposits lying on the two sides of the old Appalachian axis probably now exceeds 60,000 square miles; the average thickness of the section is certainly not less than 2,500 ‘feet; so that the amount of matter of a prevailingly coarse nature which was laid down along the old Appalachian ridge in a period apparently of no great duration was not less than 20,000 cubic miles, and probably was MON XXXIII 5 66 GEOLOGY OF THE NARRAGANSETT BASIN. far more than that amount. When we remember that the whole drainage basin of the Mississippi—a region which is probably many times as great as the field whence this detritus came—yields to erosion not more than about a twentieth of a cubic mile each year, it becomes evident that we have to bring into our conception of the causes operating in the olden day some more effective agent of erosion than is found in free water. If all the detritus of the Carboniferous conglomerates were of the same nature as that which is found in the Southern Millstone grit and the related beds, we could perhaps assume that their production was due to the invasion of the sea acting upon a deep decayed zone, but the fact that the thickest of these deposits occur in the northern part of the Appalachian field and are composed of undecayed pebbles negatives this hypothesis and requires us to assume that the erosion attacked the bed rock with great intensity. That this attack was by torrent action is extremely improbable; for, as before stated, no torrents are now known to produce so large amounts of pebbles of crystalline rocks as were formed at this time; and when such fragments are formed, so far as my observations go, they always present marks of decay, due to the slow manner in which they are shaped and to the conditions of their storage in detrital cones. The pebbles of the Narragansett and other conglomerates of the same age which I have examined, even those of a compound nature, are in practically all cases as fresh as those contained in the bowlder deposits which were formed during the last Glacial period. This appears to negative the supposition that they could have been the result of ordinary torrent action and to require a method of formation which apparently can be explained on the hypothesis of glacial erosion. It should be noted that the pebbles of the Carboniferous conglomerates, especially in the Narragansett district, show no trace of glacial scratches; moreover, they generally have a rather rounded form and are of less varied size than those in any of the till deposits formed during the last Glacial period. In some cases, however, they seem to me to retain the faceted shape which is so characteristic of ice-made pebbles. When compared with the pebbles of the last Glacial period, which, in a measure, have been sub- jected to marine or stream action, they are found to correspond with them in all essential features, except when, as is often the case, the old fragments. have been deformed by stresses which came upon them since they were GLACIAL PHENOMENA. 67 built into the Carboniferous strata. The absence of large bowlders in the Carboniferous is paralleled by what we find in the modern washed drift; there, as might be expected, the larger fragments have been kept out of the beds by the sorting process which takes place in water transportation. The facts disclosed by a study of the conglomerates of this basin lead to the conclusion that the pebbles were probably formed by glacial action, and that the fragments were brought to their present position by torrents which swept into the basin from the highlands that bordered it. Their transportation to their present sites, as well as their distribution into beds, may have been due to waves and shallow-water currents acting during a period of increasing depression of the land. In no way save by glacial work does it seem to me possible to account for the rapid formation of the great mass of pebbly detritus which is contained in these beds. It therefore may fairly be held that the Carboniferous period, in this district at least, was one of extensive and long-continued glacial action, and that the greater part of the section exhibited in the basin is made up of rocks which owe their more important features to the action of glaciation. From the Carboniferous to the Pleistocene this area affords no evidence of ice action. LAST GLACIAL PERIOD. The last Glacial period has left upon this district marks of its action which are as indubitable as any that are found im the region to the north- ward. In the time of the greatest southward extension the front of the ice evidently lay considerably to the south of the whole southern shore of Mas- sachusetts, Rhode Island, and Connecticut. This is shown by the presence of extensive moraines on the Elizabeth Islands, Marthas Vineyard, and Nan- tucket, as well as on Long Island, New York. A careful inspection of the marine soundings off this shore has failed to reveal any indications of a submerged moraine marking the extreme line to which the ice sheet attained. Moreover, the evidence gained by the study of the front over the land from the coast of New Jersey to the far West goes to show that the extreme extension of the ice was of a very temporary character, the considerable halts having taken place in the stages of retreat which probably began very shortly after the farthest southward advance had taken place. The stages of retreat of the glacier in and near the Narragansett Basin are fairly well marked by the occurrence of frontal moraines. These 68 GEOLOGY OF THE NARRAGANSETT BASIN. moraines consist in part of ridges composed of glacial waste, in charac- teristic, irregular, shoved attitudes, each ridge with a more or less distinct sand plain or frontal apron on the side which lay away from the ice, and in part of bowldery tracts where the glacier did not build a distinet or frontal wall or where it may have overridden or broken down the barrier after its construction. It should be noted that these moraines, unlike those on Long Island and Marthas Vineyard, are not placed at right angles to the general trend of the ice movement, but on the west side of Narragansett Bay are turned into a nearly north-and-south position. Beyond the head of the bay they again turn more nearly to the east- and-west direction. On the eastern side of the basin the ridges are not traceable with sufficient distinctness for mapping, but the outlines of the ice front at the time of the formation of this moraine are well enough shown to make it plain that there was a deep indentation at that point, so that while the ice overlapped the present shore on either side of the basin the front did not extend much south of Taunton. Such lobations of the margin, as they have been termed by Chamberlin, were very common along the front of the great ice field. They are due to irregularities of the surface over which the ice moved or to other local conditions. In other instances the presence of a deep, broad valley, such as is afforded by the channels of the Narragansett Bay, led to the projection of the ice at its mouth beyond the main line of the front. In this instance the retreat of the front was probably due to great volume of the subglacial streams which flowed from the areas to the northward. Their effect on the ice at the margin would be to melt it away at the base, making the formation of ice- bergs an easy matter. As the region was evidently depressed below its present level at the time the ice was most advanced—lowered, it may be, to some hundreds of feet below its present altitude—the undermining action of the waters would naturally tend to detach bergs. It is evident that the ice front in the region between the northern part of the basin and the sea was subjected to many alternations of advance and retreat which are not registered in any distinct moraines. About twenty years ago, when the Old Colony Railroad Company was widening its road- bed, the new-made sections distinctly showed that there had been a score of these oscillations in the line from North Easton to Somerset, each marked by the disruption and erosion of the deposits which had previously been GLACIAL DEPOSITS. 69 formed at the front of the ice. The same evidence is visible at the present time, though less distinctly, in similar cuttings which are making from Brockton southward. The result of these irregular movements of the ice has been to give the drift deposits of this field a peculiarly irregular and confused character. The greater part of the eskers or ridges ef sand, gravel, and bowlders which were formed within the ice-carved channels that were excavated by the subglacial streams has been effaced. It is a notable fact that inthe southern part of the basin, on the shores and islands of that part of it which is included in Rhode Island, eskers are essentially absent, except near the moraine which borders the western margin of the field. This seems to be due, not to the successive advances and recessions of the ice front, but rather to the fact that the very deep chan- nels of the bay provided ample low levels through which the subglacial streams made their way to the sea. In the district between the railway bridge at Somerset and Steep Brook Station there is an extensive and very characteristic area of those ‘‘pitted plains” which are often found near where a subglacial stream discharged its current into open water. The area which now remains is evidently only a fragment of the original field. The materials seem to have been brought to their position by an under-ice river which followed in general the line of the present Taunton River. The cause of the pittings is not yet determined, but they are probably due to the embedding of masses of ice in the swiftly accumulating detritus, these small bergs being weighted down to the bottom by the amount of rocky matter which they contained; when they melted, the originally level surface fell into its present shape. The till or bowlder-clay coating of this district is, on the average, less thick than in the region lying immediately to the northward; wherever the section extends to the bed rock this most general element of the drift—the waste dropped on the rocks in the last retreat of the ice—is commonly found to have a thickness of less than 10 feet. Although this till sheet, when it covers rounded masses of the bed rocks, often takes on a drumlin aspect, it seems clear that there are none of these peculiar lenticular hills in the basin. Their absence on the margin of this part of the continental glacier is in accord with their distribution in other parts of this country; they are evidently due to the conditions which prevailed in the portion of the ice which lay near the margin, but not usually within 50 miles or so of its verge. 70 GEOLOGY OF THE NARRAGANSETT BASIN. It is to be noted that the till materials of this basin contain a much smaller amount of clay than is the ease with the like deposits farther inland. This is probably due to the fact that in this marginal district the materials composing the till consist largely of esker and other washed gravels that had already lost their clay element. In the irregular movements of the ice and of the subglacial streams a large part of this clayless matter is brought again into the ice, and in the end finds its way to the surface in the form of till, The result is that in this marginal portion of the glacial field in New England there is often little difference in the materials which go to make up till or kame deposits, the clay element having been in both cases washed away. The effect of this is to make the value of the fields for tillage much less uniform than is the case where the till deserves its ancient name of bowlder clay. The origin of the glacial detritus of the Narragansett Basin has not yet been fully traced. From the studies which have been made it is suffi- ciently evident that the carriage in the case of the materials contained in the till has in general been for no great distance. Although, as will hereafter be noted, there is at least one case where the transportation has extended very far, the evidence shows that at least four-fifths of the till débris has been carried not more than 5 or 6 miles. This determination is easily made on the northern border of the basin, where the line between the pre-Cambrian and igneous and the Carboniferous rocks can be traced with approximate accuracy. The materials which have been conveyed in the subglacial streams, here as elsewhere, have been subjected to much greater transpor- tation. The exact extent of this has not been determined, but it has probably amounted to many times the distance of the carriage of the materials which form the till. A large part of the waste which enters into the composition of the drift of this district has come from the disintegration of the conglomerates of the Carboniferous section. This is shown by the fact that a considerable portion of the drift pebbles retain the distinct form which was given to them by the stresses to which they were subjected in the beds in which they had lain so long, and also by the fact that these pebbles are often composed of the fossiliferous quartzite which yielded so much to the débris in the Car- boniferous time, but does not now exist in the original bedded form in any part of the district. The fact that the glacial deposit in the older moraines GLACIAL EROSION. 71 contains relatively few large bowlders which have been derived from the conglomerate, while the pebbles from that source are extremely abundant, is worthy of note. Thus, on Marthas Vineyard, where the bowlders and pebbles which lie on the Cretaceous and Tertiary rocks have all been imported from the Narragansett Basin, the amount of pebbles which have been separated from the matrix of conglomerate is very great, but the number of bowlders of the conglomerate rock is so limited that an inspec- tion of a thousand of these erratics revealed only half a dozen of this nature, the others being from the granitic and other old rocks which form the margins of the basin or from some of its inliers of like rocks. In its ordi- nary undecayed state the conglomerate fractures in such a manner that the rift intersects the embedded pebbles. We are therefore justified in believing that at the time the glacial flow began to attack this region the deposits were decayed to a considerable depth, so that the attrition broke up the adhesions and separated the pebbles from the matrix. The fact that the bowlders of the massive conglomerate are very rare in the moraine of Marthas Vineyard, which was formed at an early stage of the ice time, while they are relatively much more common in the drift lying in the basin, gives support to this view. It is certain that the débris from this basin which is found in Marthas Vineyard was derived from the area in the earlier stages of the glacial excavation, while that formed on the surface of the conglomerate represents, of course, the last part of the erosion which was effected. AMOUNT OF EROSION. Although the amount of erosion which was accomplished by the ice in the last Glacial epoch can not well be determined, the evidence goes to show that it was considerable. Thus the moraines in Falmouth and on the island of Marthas Vineyard and the Elizabethan group, all of which appear to owe their materials in the main to the rocks of the basin and its margins, contain in the aggregate a mass of matter which, evenly distributed over the basin, would cover it to the depth of several feet. It is not to be believed that these accumulations represent anything like half the rocky matter which was worn away from the Narragansett district. Better evidence as to the amount of erosion, as well as much information concerning the distance to which the drift has been carried, is afforded by the bowlder trains of this field. These trains are traceable from certain of the peculiar 2, GEOLOGY OF THE NARRAGANSETT BASIN. deposits of the district to distances which vary with the endurance of the particular kinds of rock. The crystalline limestones of Lincoln form trains having a traceable length of from 4 to 5 miles; after a journey of that length the rather soft bowlders seem to be quite worn out. The exceed- ingly hard ilmenitic magnetite which occurs in Cumberland near Woon- socket, Rhode Island, has yielded the most perfect bowlder train that has yet been traced in this section of the country. Origimating in a deposit which has a width transverse to the path of the ice of only a few hundred feet, this train extends in a gradually broadening path to the outer or southern part of Narragansett Bay in a nearly north-and-south course; thence it appears to have been deflected easterly, so that it overlapped the western peninsula of Marthas Vineyard, known as Gay Head. In that district four or five specimens of the unmistakable rock have been found, which afford sufficient evidence that the train extended at least 60 miles from the point of origin. In a description of the Iron Hill bowlder train,’ I have given a detailed account of its phenomena; and an estimate, based on such data as were obtainable that served to show the amount of the rock in the deposit, was that the amount of erosion which had taken place at Cumberland Hill during the Glacial epoch was not less than 60 feet. In reviewing the facts, it seems to be evident that this estimate is under rather than over the truth. It is not unlikely that if all the waste from this elevation which was removed by ice action could be restored, the summit would be near 200 feet above the present level. It is not to be supposed that the amount of erosion in the Narragansett area was as great as that which occurred at Iron Hill. At the time the ice began to act, that mass was probably at a much higher level in relation to the surrounding country than it is at pres- ent; it is likely that the processes of decay had penetrated deeply along the numerous joints, so that when assailed by the ice it rapidly broke up. However, making what seems to be all due allowance for this probably greater erosion in this point, it must be confessed that, taken with the evi- dence before adduced, it serves to show that a considerable thickness of beds, perhaps near 100 feet of rock, must have been worn from this area during the time the ice lay upon it. 1The conditions of erosion beneath deep glaciers, based upon a study of the bowlder train from Tron Hill, Cumberland, Rhode Island, by N. 8. Shaler: Bull. Mus. Comp. Zoél. Harvard Coll., Vol. XVI, No. 11, January, 1893, pp. 185-225, 4 pls. and map. CHANNELS OF BAYS. 73 It is well to contrast the rapid and effective erosion work of the conti- nental glacier with the relatively very slight action that tree water or atmospheric decay has had upon the rocks of this district since the ice mantle passed from its surface. Since the surface entered on its present state there has been but very little decay of the rocks. ven where they have remained without a covering of soil, as is the case in the summit of Iron Hill, the penetration of decay in most instances is inconsiderable, and the actual loss of material is so slight that the lowering of the surface has not on the average exceeded 2 or 3 inches. In some cases bosses of the harder conglomerate which have had no other protection than a coating of lichens and the thin layer of detritus which they gather on a steep slope, still retain the deeper groovings which the ice impressed on them. So far as the bed rocks are concerned, the removal of matter from this region since the close of the last Glacial period has been entirely unimportant, and the decay, such as has penetrated so deeply in the Southern States, has hardly begun even in the most advantageous situations for the process. These facts point to the conclusion that the period which has elapsed since the ice left this district has been, in a geologic sense, very brief. It is to be noted that the channels in which the main arms of Narra- gansett Bay lie are still rather deep, though their bottoms are probably coyered by a considerable thickness of drift materials, both that which was originally deposited when the ice was retreating and that which has been swept to its place by tidal action. The question suggests itself as to what extent these depressions are due to the direct cutting action of the ice and what to the concomitant action of the subglacial streams. While it must be admitted that the general distribution of the channels of the bay and their relation to the river channels connected therewith favor the supposition that the arrangement of the valleys is in the main the result of ordinary river actionyit can not well be denied that the glacial work ereatly changed the forms and in a measure the distributions of these depressions. Thus the several rocky islands of the bay, with deep water between them, can not well be explained by the supposition that they are the remains of divides which once separated adjacent parallel river valleys. The channel between Bristol Neck and the north end of Aquidneck Island appears to be inexplicable on the theory of a submergence of river topography, but it may be accounted for on the assumption that it is due to glacial scouring. 74 GEOLOGY OF THE NARRAGANSETT BASIN. It is to be noted that the general form of the basin is such that the ice during the period when its front lay beyond the present shore line of the continent, as it probably did for the greater part of the time in which it occupied this part of the country, was led somewhat to concentrate its flow in the relatively narrow space occupied by the seaward part of the basin. This concentration must have increased the speed of the move- ment and thereby the erosive effect of the moving ice. I have elsewhere* endeavored to show, by clearer examples. than are afforded by this field, that the effect of such an increase of speed, due to the crowding of ice into a relatively narrow way, is to intensify the erosive work which the ice per- forms. It is also clear that the subglacial streams which discharged into this bay were very large. Such streams, so long as they flow beneath the ice, probably have a far greater cutting power than open-air rivers, for the rea- son that they move with an energy in some measure intensified by the height of the column of ice whence they are derived. As the sheet may well have had a depth of some thousand feet, the impulse can be accounted as great. These subglacial streams were competent to urge forward over level ground the bowlders, often several feet in diameter, which we now find embedded in the eskers—masses which the most vigorous mountain torrent would hardly be able to move. We may therefore reckon the sub- glacial streams as powerful agents of erosion, quite competent to deepen channels such as the preglacial rivers may have formed or to cut new ways if the conditions compelled them to flow in other courses. It must be said that the form of Narragansett Bay is not that of a characteristic fiord, such as in the regions farther to the northward clearly attest the competency of glacial ice to excavate such basins. There is no trace of the sill or rock barrier across the mouth of the bay, separating it from the sea, such as marks the normal Scandinavian fiords. We may, however, hold that while this Narragansett system of depressions is clearly, as regards its general outlines, the product of erosion work done before the ice time, it owes much of its form to glacial processes. Before closing this brief account of the glacial phenomena of the Nar- ragansett district which demand notice in this memoir, we may refer to the general form of the surface of the basin with reference to the possible effect 'The geology of the island of Mount Desert, Maine, by N.S. Shaler: Eighth Ann. Rept. U.S. Geol. Survey, Part II, 1889, pp. 1007, et seq. DECAY PRECEDING GLACIATION. 15) of ice action in shaping the area. The facts presented in this report clearly indicate that the bed rocks have been cast into exceedingly varied flexures and faultings. As these disturbances involved a great thickness of strata aud were made apparently in a geologically short period, the result must have been the formation of mountains of high relief. Yet these elevations have been so completely effaced that, as is shown in the maps, the region is now in the state of a great plain, the trifling differences of elevation being due to the action of the rivers and the subglacial streams. As before remarked, the modern school of geographers would attribute this topographic character to the process of base-leveling, by which, through the atmospheric agents of erosion, a surface, however diversified, tends inevitably to be low- ered to near the level of the sea. Making what seems to be due allow- ance for the effect of repeated elevation in refreshing the work of the streams and thus promoting the degradation of a country, a cause which most likely operated in the West Appalachians more effectively than on this seashore, there still seem to be needed some agents to explain the remark- able planation of the district we are considering. It is likely that glaciation has been one of those auxiliary agents. We will now consider the way in which it may have operated to bring planation about. The evidence has been noted which goes to show that the rocks of this basin were deeply decayed at the time the work of the last Glacial period began. Acting on such a surface, the ice would quickly become burdened with an excess of débris,in which state it would resemble an ordinary stream of water which has a charge of sediments much greater than it can carry. In this case both the fluid and the viscous streams necessarily tend to deposit a part of their burden and to flow over the accumulations, being thus in part excluded from contact with the bed rock. The deposits of the overburden would naturally take place in the valleys, the floors of which, except when attacked by the subglacial streams, would remain uneroded, while the higher-lying parts of the field would be cut away. As the process of erosion advanced and the waste from the elevated places became smaller in quantity, the glacier would be free to attack the lower levels. The result of this succession of events would be to level off the inequalities of a country which, owing to the decayed state of the rocks at the time the ice came upon it, afforded detritus more rapidly than the machinery of transporta- tion could bear it away. It may be remarked that the apparently excessive 76 GEOLOGY OF THE NARRAGANSETT BASIN. degradation of Iron Hill, as above noted, can be explained in this way. It therefore seems reasonable to adduce ice work as one of the agents which have served to bring about the destruction of the original topographic reliefs of this district. Along with base-leveling and ice work, there is another class of agents which have doubtless operated with much effect in bringing the district into its planed-down state. These are the forces which act at and below the level of the sea. There can be no question that the effect of the surf and the shore currents is to plane off the rocks and to bring about such topo- graphic conditions as are found in this basin. The only doubt is as to the rate at which the work may go on. Judging by the speed with which the benching action of the sea proceeds where the attack is delivered on hard (i. e., undecayed) rocks, geologists have generally assumed that the aggre- gate work which is due to this action is relatively small, that it plays no important part as compared with base-leveling due to atmospheric agents. We must remember, however, that what we know of the extent of super- ficial decay in this and other countries requires us to believe that in the oscillations of the continents it must often happen that deep sections of rocks which have been made very friable are exposed to the mill of the surf. In this case it is fair to presume that they might be swept away with some- thing like the speed which is exhibited in the disintegration of the Pliocene cliffs of Marthas Vineyard. When they face the open sea, these deposits, in coherence comparable to the decayed beds of the Southern Appalachians, are retreating at the rate of about 3 feet per annum, as determined by fifty years’ observations. At this rate the surf mill would be able to work inward across the field of the Narragansett Basin in less than one hundred thousand years. CEA PAL Role Ve ECONOMIG RESOURCES OF THE BASIN. The economic resources of the basin include the soils, the pottery clays, a limited range of building stones, certain iron ores, and the coal beds of the Carboniferous series. SOILS. The soils of this region, being in the main of glacial origin, have the economic stamp of deposits which are more or less directly related to the ice work. When, as is the case in the greater part of the district which lies at more than 50 feet above the sea, as well as in much of the lower ground, the soil rests upon bowlder clay, its fertility depends to a great extent on the nature of the subjacent rock. If this be conglomerate, as is the case over a large part of the central portion of the basin, the soil, because of the generally insoluble nature of the detritus from these beds, is character- istically lean. When it rests upon sandstones it is of moderate fertility. Where, as in the region about Newport, and generally on Aquidneck Island, the underlying rock is of shale, the soil is of more than usual value. The considerable organic matter of these beds apparently serves to make a richer field for the plants. As compared with other portions of New England, this basin abounds in glacial sand plains. These occupy the larger part of the surface below the level of 50 feet above the sea, and a considerable area of higher-lying ground. The relatively great extent of these plains seems to be due to the fact that the existence of the extensive depression of the Narragansett Bay made it the point of discharge of streams collected beneath the glacier, which bore great quantities of débris beyond the retreating ice front and deposited the sandy portion of this detritus in the shallow water of the sea, which then covered the area. These sand plains are composed mainly of siliceous materials, and afford infertile soils. They are, however, of a quick 17 78 GEOLOGY OF THE NARRAGANSETT BASIN. nature, responding at once to manuring. Moreover, they are readily, though temporarily, much improved by plowing in green crops, the store of vegetable matter thus introduced into the earth serving to promote the solution of the feldspar, mica, etc., which exist in the mass, though the quan- tity is not considerable. These sand-plain soils, because of the absence of bowlders, are easily tilled; they can at certain points be readily irrigated; and they thus are likely in the modern time of intensive agriculture to be valued more highly than heretofore. The inundated lands of this district include a small area of marine marshes and a considerable extent of fresh-water swamps. On account of the limited range of the tides along this part of the coast, the reclamation of the marshes can not be easily effected by diking. These areas will therefore not receive further consideration. The fresh-water swamps, including in this group all the lands which are made untillable by tempo- rary flooding in the planting season, occupy an aggregate area of about 45 square miles, or nearly 28,000 acres. The larger part of this swamp area is to a greater or less extent used as a source of water supply for mills, the waste of the flood times being there stored for use in droughts. Until this use of the swamps is abandoned it will not be possible to win any large portion of these over-watered soils to agricultural use. About one-third of the total area consists of bogs of limited extent, which do not serve as reservoirs and are therefore open to improvement. In most instances these fields can be readily drained by means of inexpensive ditches. When so unwatered, the areas afford soils of two distinct groups. Around the margins of each area there is normally a belt where the peaty matter has not accumulated to a thickness of more than a foot, and where, after being allowed to dry, and consequently to shrink, it can, by deep plowing, be incorporated into the soil. In these portions of the drained swamps tillable fields of very superior quality may be obtained. Within the area of the basin there is probably a total extent of not less than 6,000 acres that is thus available for agriculture. Such ground is remarkably well adapted to market gardening. When the peat of a drained bog much exceeds a foot in thickness, it is difficult to reduce the area to ordinary tillage. The only effective way of accomplishing this result is by securing condi- tions of exceeding dryness by extensive ditchings, after which the peat may be burned, as is done in northern Kurope. In the present condition of our COAL BEDS. 19 agriculture this method may be deemed inapplicable. Therefore the only use which can be made of these bogs is for plantations of cranberries. In the method of cultivation which is commonly employed with that plant, several thousand acres of these drainable lands, especially the areas in the eastern parts of the basin, are well fitted to this mode of tillage. COALS. The coal beds of the Carboniferous series afford the most important economic resources of the basin. As is indicated in the portions of this memoir which have been prepared by Messrs. Foerste and Woodworth, these beds are probably limited to the lower half or shale-bearing portions of the great section. So far as is known, no deposits of any importance exist in the zone of the upper conglomerates. The exhibition of these coals is the clearest in the region where they have been most extensively mined, on the western side of the northern part of Aquidneck Island. At this point they are seen dipping to the eastward near the surface at an average angle of about 30°, with a diminishing slope as the workings penetrate toward the center of the syncline. In this section at least two coal beds occur, the lowest of which is about 2,000 feet below the base of the upper conglom- erates, and the highest within perhaps 1,000 feet of that line. In the western and northern parts of the basin the same or other coal beds occur. Of these, the deposits in or near Pawtucket and at Cranston are the best known. 'The bed at Pawtucket—there seems to be but one— lies apparently several thousand feet farther down in the great section than the beds of Aquidneck. It is likely that this bed is continued southwardly near the margin of the basin to near its southern end, and that the various exposures which have from time to time been made along this line lie upon it. It is also probable that the coal along the northern part of that border, as far as Wrentham, is of the same or a closely related stratum. The bed of coal in Cranston may most reasonably be regarded as equivalent to one of those in the Aquidneck section. Its position in relation to the upper conglomerates, however, can not be ascertained with any certainty; so its place must be left in doubt. The coal beds which were at one time worked in Mansfield are in such a position that they can not be safely placed in reference to the other known deposits. The relation of the beds to one another and to the immediate 80 GEOLOGY OF THE NARRAGANSETT BASIN. section in which they lie inclines the observer to the opinion that they are the equivalents of the uppermost at the mines on Aquidneck Island; but this opinion has little evidence to support it. ~ Many other deposits of coal have been occasionally exposed in various parts of the field in which the carbonaceous strata occur. Some of these, as, for instance, the beds at Bristol, have been made the objects of experi- mental mining. The last-named deposit is, from its position, to be reckoned in the group occurring in the northern part of Aquidneck, but the greater part of these little-known occurrences can only be placed as below the upper conglomerate. CONDITION OF BEDS. As none of the coal beds of this district have been worked for many years, the accounts of the deposits can not be made anew. ‘The writer has seen the bed which was last worked at the Aquidneck mines, and also that at Walley Falls, which to within a few years ago was mined for “foundry facings,” and also that which was in a small way exploited at Cranston in an unavailing effort to market it as fuel. From these observations and the imperfect records which exist of the facts concerning the other deposits, the following statements may be made as to the physical conditions of the deposits. The coal beds of this area probably number a half dozen or more, of which only those of the Aquidneck group have been proved to have much continuity. Owing to a feature which, so far as observed, they all present, the thickness of none of these beds can be accurately determined. This feature is the peculiar “rolling” to which the carbonaceous material has been subjected in the dislocation of the beds of which it forms a part. In practically all cases the beds above the coal have been by the process of metamorphism brought into a very compact and rigid state. This change appears to have taken place before or during the development of the folds into which they have been cast. As the process of dislocation went on, the irregular strains acting on the relatively little resisting coal caused it to creep toward the points of least pressure. The result was that wherever the bed has been followed in the direction of the dip for a considerable distance the layer is found to widen and contract, so that in a variable length POSITION AND EXTENT OF COAL BEDS. 81 of from a few score to 600 or 800 feet it may pass from a mere trace to the thickness of 20 feet or more, the cross section having a rudely lenticular form. Followed horizontally, these thick portions of the vein thin toward either end—at least that is the impression made by a study of the Ports- mouth mine. So far as could be seen there, the horizontal dimension of the lens was much greater than that shown in descending the slope. It is evident that these conditions exclude any careful study as to the thickness of the beds. It may be said that a rough computation of the contents of the principal bed mined at Portsmouth showed it to be probable that the thickness of the deposit before it was disturbed by the shearing action was not far from 44 feet. It need not be said that this irregular form of the coal deposits, com- bined, as it is, with a certain amount of faulting, which, though not dis- tinctly shown in the small workings, is evident in the structure of the field, makes it important to determine how far these features are general through- out the basin. On this point the information is very scanty. It may be said, however, that where, as in the Portsmouth mine, the workings had gone for a distance of about 1,400 feet from the outcrop, and where the steepness and the dip considerably lessened with the approach to the center of the syncline, the irregularity of the bed had perceptibly diminished, giving some reason to expect that there was an extensive area of coal in that cen- tral part of the trough which had not been much dislocated. Unfortunately, this is the only portion of the basin where there is sufficient basis for reck- oning that the coals within reach of mining work occupy a position which gives them the chance of escaping the effects of ‘“rolling.” Owing to the lack of detailed knowledge concerning the position of the coals, or even of the precise attitude of the rocks in this basin, it is not yet possible to estimate with any approach to accuracy the area in which coals of workable thickness may be found. It may be said in general that all parts of the section lying more than 2,000 feet below the base of the upper conglomerates show, from point to point, traces of coal. Consid- ering the numbers of these chance exposures, and noting the general way in which the portions of the section containing coal are hidden by glacial detritus, there is reason to believe that a considerable part of the rocks below the indicated level are in some measure coal bearing. Definite MON XXXIII 6 82 GEOLOGY OF THE NARRAGANSETT BASIN. information as to the extent and thickness of these beds can not be had without extensive and systematic exploration with the drill, but some results could be obtained hy well-planned. superficial excavations. It should be noted that, owing to the thickness of the barren upper part of the section of the rocks in the basin, nearly one-fourth of its area has the coal-bearing beds so deeply buried that they are belew the level where they could be mined; in much of the area the estimated depth exceeds 10,000 feet. Moreover, nearly another fourth of this area is occu- pied by the waters of the sea, so that it may be regarded as impracticable to explore the underlying rocks. The remaining half is fairly open to inquiry provided there should be found a market for coal of the peculiar quality which it affords, at a cost which would be imposed by its physical and chemical conditions. These we will now note: CHARACTERISTICS OF THE COALS. Wherever found, the coal of this basin has certain characteristics which distinctly separate it from any other fossil fuel that has been mined in this country. The material is everywhere extremely anthracitic, often ranging in appearance toward graphite. It is usually much penetrated by veins of varied and rather complicated nature. It is high in ash, the pro- portion commonly being 10 per cent, and often attaining to near twice that amount. This ash contains in most instances a singularly large amount of lime, which causes the cinders to smelt and thus clog the grate bars of a stove or boiler furnace. As is shown by the accompanying analysis, the percentage of fixed carbon is abnormally high, yet an extended trial of the coal in producing steam showed that the value for this purpose was but 72 per cent of that of Lackawanna coal. The reason for this disproportion may have been in part the lack of adaptation of the fire boxes to the character of the fuel, which evidently needs a very strong draft, and the fusible nature of the slag, which makes it difficult to keep the grate bars clean. It is possible, however, that a portion of the carbon is in some special chemical state which hinders its ready combination with oxygen, perhaps in the condition of the supposed graphitic acid of Graham. COAL ANALYSES. 83 Analyses of coal from the Portsmouth mine, Portsmouth, Rhode Island. ' {Analysts, Dr. F. A. Gooch and Mr. B. T. Putnam.] | T II | IIt. | TVS Wee i evils | Vil. | VIII. | ID. | | RS yee | | sw Wiarteriase ete oa Saar | 5.12 | 0.52 | 3.18 | 2.95 | 7.62] 7.96] 8.76 “oF | 20 47 | Volatile combustible ...| 6.49 | 6.31| 4.43 | 6.46) 5.42] 4.95] 7.23| 5.99) 5.83 | | | = @anboneiasreeee 55. 71.04 76.23 | 75.97 | 79.5.) | 74.40 | 76.22 | 70.24 | 67.50 | 66.95 | | | ING ps Seea EUS hese | 17.35 | 16.94 | 16.42 } 11.70 | 12,56 | 10.87 | 18.77 | 16.24 | 17.05 100.00 100.00 |100.00 100.00 100.00 |100..00 100.00 100.00 |100. 00 | | | | liSulpligsse eee. Oe 16x Oq 2241105258] 0:64! 50528 || eee jee een nade rere IA Ghit Setoeulensee mois. | Red.:| Red. | Red. | Red. |.....-- lRedsilaeRedsa eee noeene Fuil ratio Feoeor) | 10.94 | 12,08 | 17.14 | 12.32 | 13.72 | 15.39 | 9.71 | 11.26 | 11.48 | Vol. Comb. | | | | | | | | | | I. Bottom of shaft, north side; thickness of seam, 3 feet 11 inches. II. Bottom of shaft, south side; thickness of seam, 2 feet 7 inches. III. South side, 50 feet from bottom; thickness of seam, 6 feet. IV. South gallery, 370 feet from bottom; upper three-fourths of 6-foot seam. (Analyses IJ, IT, III, and IV are from samples taken across the width of the seam.) V. The average of seven analyses made from samples taken at intervals along the length of a 6-foot drill core, cut out of what is known as the “back seam,” at about 90 feet below the mouth of the Portsmonth mine. Vi and VII. The single analyses of this series showing the maximum and minimum percentages of carbon and ash. VIII and IX. Samples taken from two lots, of several tons each, of freshly mined coal used in other experiments. Although it is probable that if the coal can be mined in the undisturbed central parts of the shallower synclines it will there be found to contain less vein matter, and hence will be lower in ash, its high percentage of the latter and its other objectionable peculiarities may have to be reckoned as insu- perable. It is therefore very doubtful whether it can ever be brought into service for ordinary uses. The experiments heretofore referred to appear to show that it can not be given a fair place for steaming purposes. The fact that while the Portsmouth mine was working, the people o: the neigh- borhood were not willing to pay more than two-thirds of the cost of Penn- sylvania anthracite for its product, shows that it is not well suited for house- hold use. There remain, however, as before remarked, certain fields in which this fuel may well find a place. These are ore smelting, the manu- facture of water gas, and the process of burning brick when the powdered coal is placed between the layers of the kiln. 1Notes on the Rhode Island and Massachusetts coals, by A. B. Emmons: Trans, Am, Inst. Min. Eng., Vol. XIII, 1885, p. 511. 84 GEOLOGY OF THE NARRAGANSETT BASIN. As to the first of the aforenamed uses, it may be said that the coal of this basin seems to be fairly well suited to the needs of smelting. It is low in sulphur; its specific gravity is so high that it will give a large number of heat units for a given bulk; the ash, though high, is, owing to its composition, easily smelted. I was told by the person who owned the mine at Portsmouth the greater part of the time during which it was worked, that the coal was the best that could be obtained for smelting copper ores as well as for the subsequent working of that metal. The further statement was made that a cargo of the fuel had been sent to. an iron furnace on the Hudson and that it proved very satisfactory as com- pared with the anthracite of Pennsylvania in making Bessemer pig. I was also informed by one of the Crocker Brothers of Taunton, Massachusetts, who worked the mine, that a test of a few tons of the coal had been made in the manufacture of water gas and that it was well suited to the purpose. It is not now possible to verify these statements, but they appear to be quite consistent with what is known of the nature of the anthracite of this field. The only undetermined qualification of the Narragansett coals as regards their use in the special arts above mentioned is that observed by Dr. Arthur B. Emmons and described in the paper referred to. This, in the words of the author, is “the striking peculiarity (hitherto unnoticed in anthracite coals, or, I believe, in any coals) of quickly taking up a large per- centage of water under a moist condition of the atmosphere and as readily parting with it under a drier condition of the atmosphere.” According to the records obtained by Dr. Emmons and his collaborator, Dr. F. A. Gooch, the Narragansett coal may, with the changes in the humidity of the air, vary as much as 15 per cent of the whole weight of the material. How far this peculiarity may affect the value of the coal in the smelter or water-gas converter will have to be determined in an experimental way. In considering the prospective value of this coal, the cost of mining it is of course a matter of much importance. So far the practical experiments in mining have been too few and too imperfectly executed to afford any clear determination. The mine at Portsmouth, the only one in the basin maintained in operation for any considerable time, was not well managed. As the deep part of the pit was almost absolutely dry, the little water found in it entering from the old upper workings, there was but slight expense for pumping, the drip collected in the sump being hauled about once a month EXPLORATION FOR COAL. 85 in one car. The roofs of the seam were admirably strong, requiring practi- cally no timbering even where the pillars were robbed to a very extreme point. At the time I last examined the place the best information which could be had indicated that the cost of lifting the coal and treating it at the breaker amounted to about $2.50 a ton. An estimate based on a suitable amount of surface plant and proper approaches to the vein, with a fit admin- istration, indicated that at the present price of labor the coal could be mined, so long as the bed was in the then existing favorable position, for about one- half the sum it was then costing. If the coal is found as a little-distorted bed, averaging say 4 feet thick over as much as 3 square miles in the cen- tral part of the basin, it should by means of vertical shafts be possible to mine it at a yet lower cost than that named. CONDITIONS OF FUTURE ECONOMIC WORK. As to the best places for future exploration, it may be said that it seems to be undesirable to undertake any further search for the coal at the outcrops, the presumption and the evidence being alike in favor of the opinion that at such places the coal, lying at a steep dip, is more likely to be much infiltered with vein matter. The aim should be to seek the beds in the central parts of the synclines, or where, though monoclinal, the strata have a low dip. The best of these places appears to be that in the northern part of Aquid- neck Island. If the apparent diminution in the slope of the strata toward the center of this trough be verified, there is a reason, before remarked, to expect a considerable area of the coal beds in the central part of the north- ern end of the island, where the rocks seem a little disturbed. There is no very clear evidence as to the depth below the surface at which the coal may lie, but it seems quite probable that this depth is less than 1,800 feet in the central portion of the area. ‘To determine the true position of the deposits, a line of borings should be carried across this part of Aquidneck Island in a nearly east-west direction, with its western end about 500 feet from the vertical plane where the old workings stopped. It will be well to supple- ment the information thus gained, especially if the indications so obtaided are favorable, by other borings carried southward toward Quaker Hill. The next most promising field for exploration is the belt of country lying immediately to the east of the northward extension of the Providence 86 GEOLOGY OF THE NARRAGANSETT BASIN. River, where, if the determinations of the structure as set forth in this report are correct, the equivalents of the Portsmouth coal beds should be found. The known facts go to show that in this part of the field the rocks are not much disturbed, and that these coal beds are in the place where it is supposed they should occur. Should these suppositions be verified, there may be an area of 20 or more square miles in which the conditions are favorable for mining operations. In connection with this part of the field, it is necessary to set forth the facts concerning a boring made in the town of Seekonk about twenty-five years ago. This gave a section of the rocks which at its base appeared to indicate the occurrence of a bed of fairly good anthracite at a depth of about 700 feet below the surface of the ground. There can be no doubt as to the fact that the bormg was made. Abundant samples of the core were examined by the writer about five years after the work was done. They were then in the possession of the man on whose land the boring was made. They showed the rocks to be of the general character of those which overlie the Portsmouth beds, and also that the beds are not very much disturbed, the dip averaging not more than 20°, probably to the eastward. An analysis of the coal showed it to have the general character of the Rhode Island deposits, being extremely anthracitic. Mr. Emmons, in the paper above referred to, states that, while the boring down to the level of the coal is the result of an honest mquiry, the coal is a fiction, the portion of the core showing the coal having been made on the ground by operating the drill several times through a large lump of coal brought by the disappomted explorer to the man who was managing the apparatus, ostensibly to find whether the instrument would cut a clean core in material of that degree of hardness. On review of all the facts, it appears worth while to reopen this drill hole, which was carefully plugged at the time the work was abandoned, and, with a reamer, to test the bottom of the opening, in order to ascertain the truth. If coal is not found, it will still be well to continue the drill work already done, down- ward as far as it may be conveniently possible to do so, for the reason that not far below the base of the present opening we may expect to pene- trate the portion of the section where the beds of the Portsmouth district belong. If the section could be carried to the depth of say 3,000 feet, the information would be of great value as related to the possibility of finding workable coal in the northern portion of the basin. EXPLORATION FOR COAL. 87 By reference to the map (Pl. XVII) it will be seen that the upper con- glomerates occupy an insular position in the northern part of the basin, in which they have been left by the degradation of the folds in which they lie. So far as has been learned, there are no faults or other local disturbances which should make it improbable that the beds equivalent to the Portsmouth coal-bearing part of the section are found in their due place in the belt of country on the north and east of this conglomerate area. It is to be noted, however, that so far no coal beds have been revealed in this belt by natural exposure or by chance excavations; but this may be accounted for by the fact that the district is much more deeply covered by the drift mantle than that to the westward and northward. Therefore this section, within say a mile of the margin of the upper conglomerates, may be regarded as next in promise to the sections before mentioned as a field for explorations. It should be observed that the angle of the dip toward the center of the Taunton or Great Meadow Hill syncline (see figs. 8, 9, in Part II of this monograph, pp. 122, 123) makes it probable that at a little distance within the margin of the coarse conglomerates the coal beds which would lie in the strata plane of those at Portsmouth would be greatly below the level where they could be profitably worked. As yet no adequate information has been attained which may serve to show the conditions of the basin in the region to the east of the city of Taunton. In that place a boring carried to the depth of 850 feet revealed no good coal; indeed, but little more than carbonaceous matter was found. The beds are presumably the equivalent of those which, in a thickness of 2,000 feet or more, overlie the coals of the Portsmouth mines. The churn drill gave, of course, no information as to the attitude of the rocks. It seems likely that there are but slight faults or folds in this part of the field, and that im the main the beds belong to the section which may be expected to contain coals. For the reasons before given, which go to show that it is not worth while further to explore for coal around the margins of the basin, there remains only one other portion of its area to consider. his is the field between Aquidneck Island and the western shore of Narragansett Bay. The greater part of this district is covered by water. All that part of it which lies to the south of the northern end of Canonicut Island is evidently so affected by regional metamorphism that any coal which it may contain is 88 GEOLOGY OF THE NARRAGANSETT BASIN. likely to be of very poor quality. The water-covered area is, as before noted, difficult to explore. If, however, coal should eventually be found beneath those arms of the sea, it could doubtless be mined with safety, though with added cost, on account of the difficulties of access. Before any further costly effort to develop the coal deposits of this dis- trict is made the coal from some one of the openings—that at Portsmouth, for instance—should be subjected to systematic and thorough experiments to determine its value in the wide range of arts to which this fuel may be applied. These tests should include at least the arts of ore smelting and the manufacture of water gas, brick, and pottery. Experiments, which on theoretical grounds appear to be very promising, should be made in crush- ing and washing the coal and in subsequently converting it into briquettes. It may be found that in this form the material will prove serviceable as an ordinary fuel. There can be little doubt that this inquiry should be under- taken. As before noted, there is a very large amount of coal in this basin, although there is no basis of reckoning the total quantity with any approach to accuracy. There can be little doubt that it is to be estimated by the hundred million tons. Even though, as has been assumed, this coal can not compete in ordinary uses with that which is imported, the chance that it may serve in many important arts affords full warrant for a careful study of its quality and distribution. The inquiry above noted could be undertaken on a lesser scale, lim- iting it to the Portsmouth field. As already stated, this is a typical area, probably the best in the basin. Work there should first be directed to ascertaining the extent, condition, and depth at which the coals occur in the central portion of the trough in which they lie. If the results obtained are satisfying, it will be easy to obtain from the existing openings enough coal to make the trials which have been suggested. Supposing these tests to show economic value, the old workings should be abandoned and the beds approached by means of a vertical shaft, so placed as to enter them as near as possible to the center of the basin. IRON ORES. The iron ores on the western border of the Narragansett Basin have a certain amount of economic interest, in that, in case the coal is ever developed, they may become of value for the purpose of mixing with the FUEL FOR SMELTING. 89 ore brought from other parts of this country or from abroad. The only iron ore of promise in this field is that which occurs at the eminence known as Iron Hill, which lies in the town of Cumberland, about 24 miles east from Woonsocket, Rhode Island. The deposit is a rather ilmenitic magnetite," containing about 35 or 40 per cent of metallic iron, but it is remarkably free from phosphorus, in this regard closely resembling the best Swedish ore, which it also resembles in its petrographical characters. The mass of the ore, apparently in its nature a dike, runs along the general surface of the country in which it lies, to the height of nearly 100 feet. It has a width of about 600 feet and is of about twice that length. It is probably con- tinued downward to an indefinite depth, and may extend for a considerable distance beneath the cover of drift to the north and south, in which axis the mass seems to trend. The mass of ore may therefore be reckoned as large; it probably could afford, if desired, a total of 10,000,000 tons or more without particularly deep workings. The limestones of Lincoln, Rhode Island, between Iron Hill and the western margin of the Carboniferous rocks, afford an excellent flux. As they appear in the form of white crystalline marble, it is probable that they also are nonphosphatic. Thus, if the coal of the Narragansett Basin proves to be as useful as a smelting fuel as it promises to be, the shores of the bay may prove to be well equipped for the manufacture of pig iron. About twenty-five years ago the coal from the Portsmouth mines was to a certain extent used in smelting copper ore which was mainly brought from South America. It was stated when this process was in operation that the fuel was satisfactory. If this was the case, there is yet another reason for supposing that the coal of this basin has a value when used in the reduc- tion of metals. As a whole the evidence thus points to the conclusion that those who undertake to bring these coals into the market will do well to look carefully into the question of their adaptation to this use. If this element of value could be verified, the basis for the development of the deposits might be found without reference to the other ends to which their product might be applied. In closing these remarks concerning the economic values of mines in the Narragansett Basin, it may be said that, as far as the coal beds are concerned, ‘See A microscopical study of the iron ore or peridotite of Iron Mine Hill, Cumberland, R. I., by M. A. Wadsworth: Proc. Boston Soc. Nat. Hist., Vol. XXI, 1883, pp. 194-197. 90 GEOLOGY OF THE NARRAGANSETT BASIN. the developments are not sufficiently advanced to enable the geologist to prove very helpful to those who desire to exploit its resources. Such indications as are here given are therefore to be regarded as suggestions rather than as definite recommendations; the latter can be safely made only when accurately determined facts, such as are obtained from extensive workings, have been gathered. GEOLOGY OF THE NARRAGANSETT BASIN Part Il.—_THE NORTHERN AND EASTERN PORTIONS OF THE BASIN : WITH A BIBLIOGRAPHY OF THE CAMBRIAN AND CARBONIFEROUS ROCKS OF THE BASIN By JAY BACKUS WOODWORTH 91 aud by a if 0 i ifs ih aie us i ya My CON TENS: Pa CHAPTER I.—The problem of stratigraphic succession..-...........---2. 22020. eee ee eee eee eoee 99 Repetition of lithological characters...-.....--..2.22.02-200 22 cece eee nee eee ee eee 100 Transition of lithological characters.......-.-....222. .2--20 20-2 eee e eee eee ee 100 Effects of igneous intrusions........-- Ibo SARS GES ERs poodEaSaadc6 Sona ceso ooo GéauaeES 101 WIGUER MOD MM cconcadose cb soaduoSeusOnd SaecesQS0Gue SEarSs ocESbe BoSEuS conGoS Baoaee 101 Tataalrinyss cyavl Tem ins 3553 Gaaooe Gdon Sade Cabs cao5 Sbe6 Seca paocoU boaKeE eC ooboKooSeeSe 101 IDDMRGE TON 5od5 send bcooap Seodbes sade boU Re eedsEE coad ceuopEubooEs coSecsaabebe bocene 101 Glennon .ood asus seen unas sess Boacadec Hoss conaceeodone endo cobS bee neood mone aeocdeS 102 BNI OMEWR I Osdocoo cass sobsud causes eed SuaUS Hounad aonouabsUbbE aes eood ce05 bade sass 103 Absence ofjartiticialbexcavatlons ones -)-erecceseeice eee eee conse clones econ cee ene eens 103 CHAPTER II:—The pre-Carboniferous rocks .-..--.. 2... --- oe 22. enn ences weno weno apaccenee 104 ANION SEIN POMOC oo Soa5 codecs cogede SouSUS Cond Booolsudo Saco ndon Boab Gena ccou Baee GooK sEaco b6oC 104 IBIAS TOMS) GENES 555 Song e600 seen osgcd0 SooudU Sbnb Baud poadan sdb s4n0 cod soe cnboocseees 104 Cumberlandgquartzitesmenseresamr eee eee seen e aerate ee eee eee cee eee een eee ea L0G ABU BONE 6555 ousb 36 S006 GH00 B60d boGoS6 Hba6e0 Doages sEbE bOdnoS BoESSHooos cono GEeE 107 Smithfiel dslumestonesrercssseseee sserceee aiser cee eae ese eee ee eee eee eeee 107 Chrnlysiiehn JRO). scoog besos so seas cbEs60 Hood caaSad acbad Habods CesEod uoSEbo sEbEed oooocOsaeE 109 ILOWGs CHMNIDTER, coac cose onb6 boas snag ondons cuosag 660055 sua cos GUE saabbeebo Socd oobobooGe 109 Middle:Campbriany (unrepresented) or-niecleeeeite eels sacle ee eieeieecel orem ieee oeen ceecee 109 Upper: Cambriankercne octet eam ee sentence clone ah, Leen Sante ean 109 Silunianyeeriody (unrepresented) mercermassce cee ecieeaciseecele ice enicecnioece cise ceieeeiece eee lS CHG POIIIGS oo5406 06 do006 S056 asbone bonde0 65 b6s0 Susu ead Sado Gods bedb by ad 50 cenOSS 113 CuaPTeER IJI.—The igneous rocks of the border of the basin....-...-----...-...-..-.2.-.-.-.-. 14 Gramitie rocks eeemtserre racket seyoelohecisiee a ae cio sree aiciceine Srecwle ele eee ee rec ee ena: JAAN OD HOUSED od5000c055 coos do coco coed asdac Gnas secu ne SbecHSesedececcesogHocece iG Granite-porp hiya ygemereetmerererinae sie seeceecleacerisan ach semeracee cece eee eeice cece 117 OURO e MONS casas cqoscoqosses badasd BGdd BEDS HHaB OOS are Basa bEoasE Sous seodceodcoEaon 117 GabbrophillstofeS haromscrrc tere cyan eters mielscctetesicciecee ce ee aie eine a eeetee i inten erent! 118 CHAPTER IV.—The Carboniferous basin...-...-....--- Gpnd0 Bodo nen bEnbesooacedeteddosodaos Osan 119 Generalistrncturerofuhe,basimme seme naan aise eile salsa raeeee ake rere ee eee 121 Maps\otetheyboundarygzofmihesbasimecaameae nee smele we eee sje cee eco eeeeneeee 124 Boundary of the basin on the north and east....-.....-.-.---.---...-------------- 125 From Cranston to the Blackstone River...............---.---.-+----------- 125 From Blackstone River to Sheldonville -...-...................--..------- 127 Connection between the Narragansett and Norfolk County basins........-. 127 Sheldonwillejcrosssfaultaescacttec se oeciee cisieinis Seite ee clone cen eee ienecnace 127 HromisheldonwvillestosoolishsHilliss serene caceeeenaecienceenicnceeaeecs 127 HoolishgHaillsfaunltes sees cessor odes snes eiciee setae eee ee cealeoee sacenwecaecne 128 HrompHoolishvHl:tosbrocktonineceecaiccecsicisne ose ncee selec eee ee eeinaeeneciae 128 HromebrocktonsomheyNorth Rivelee cess sces aoe eesieseeee eee cseee 129 Shumatuscacambpaul ties. oeen\scsceisccwinc cee sone seine ee Gates cee ee eee 129 EromsNortheRivertoakevilles-r css sececsscnicee cence aeeeroeacerer eens 129 Hrombplakevillentols teeppbrookeeeasesee a ssies=aeiecea clon een eee ee eeteeeee 130 Nnliers tose cleo ee eeeletee selale cteteleele nado AGNCHG OOCaKS SHeSnObEaedo CooSdOSedoe 130 NorthyAttleboronnliereercccrssnjoce auc oslo ie ieee ere sae wooo bee elon eae 131 INGA ECT ENT TUS) BIE) oo5 S660 suDaea bo0505 so00as Sao badcadssed esoatsase0 131 SITET sac5 6055009600000 606565000500 NS5605 500 CO008s boS0 5556 BSE Sod Sen asHe e506 131 94 CONTENTS. CuarTeR V.—The Carboniferous strata.----.---- bicoHsbacerincldoadad Sohode bode ddadah onoseeced Determination of horizons within the basin....-.-----..----------------------------------- Means of determining superposition --..----.----------------------------- +--+ +--+ -++-+---- Tabular view of the strata in the Narragansett Basin.-----.-.----------------------------- Formations below the Coal Measures.-...----- ---- ----+----- ------ +--+ +--+ ---- 0222-2 --- Pondyille group ---.---------- =. ------ ---2 <= 222 nn wn nn nn nes nina Basalvankcose Peds) sace sec ce ce ee alee mae ae alle ete elated lll at mama Foolish Hill exposures..---------------------- +--+ +--+ --------+---+-------- North Attleboro exposures..--....---------------- ----------- 0 ------------ Pierces Pasture in Pondville, Norfolk County Basin...--..----------------- Suprabasal conglomerates --...------------------------- +--+ ------ +225 002227 -2-- Millers River conglomerate -..---.---------------------+------------------ South Attleboro exposure...---..----. ---------- ------ ---- ----2----- Snacad Jenks Park exposure in Pawtucket ..--...----------------++-----------=--- Wamsutta group .-------------- --- +--+ 2-5 +222 ee ee ree re re ee eee TROL WCE AIA) = bese Coecos baad oe ec ane on do Sees HosbOD ehoSESrode ssa saso Stan eoeSsao5 Area along the northern border - ---.---.-------------~-------------++----+---- Gray sandstones of the northern border. ....--.-----.--------------------- INO AARON) EMER) 6 Cone bees pobd seen Senbecous cebu occas soscasesee saenbsaaDoSSS¢ Cmnm@lonEwANes A555 4555 seo seo ascends soeg cero Sas sacesn eso norS sh>60Ccso0 Samn@hOnGSs jood cenbisaas seostadeos sous Cpa so rjosas Sand onde odes cong Gada DSccas SIME = cbs oases hdd boss sooo sd58 Seon Hebe cseondasoo pas aeS neeaoopadesescaces (Cem IOAN Mine. ood See sed saspipbonlocoo sed aaorpee soon coeeseesood regent terns TR NORGIN BINERY soe been ote eas se babe ches robe soddadense cooece goon bnot sods eonabe Red beds in Attleboro, Rehoboth, and Norton ..-..---.------------------------ Norfolk: County areas 22-220 2-2 on a ee a nw win n= win minim SonthwAtitloporoslimestom enh eda em aye nne yes acta seer ee elt oa tletatareltelat= JTRHIGLNORO, EAINCISIOOG 5505 cosesacopoep eaaH pond sono cous ecce Gone sesdonscanbeoo Osco Igneous associates of the Wamsutta group ..---.-----.------------------------ IDWARRE coacas set ace qceesochenepesopod soso uoscan osde cob pcoeeSo css aca ceds Quartz=porphwyCOwUp) ses = ci =r alate ala ala lala aaa annals Diamond Hill quartz mass’. .---- - en ee oe nnn em main ai = Wyeast) SrOMCe AMOS) | Sao Sec esa odessa pode code ESdbiGacd ones osogS nope boéaadedse Folding of the Wamsutta group ....-----.-----.-------- ----------+++++---+----- IP Kove) Ce WAV) WENO IE) ARON) 585 Boob aco aces becd SSecs= Sos uesee6 ood esoe Gennes Ohya, WIGRGUI y= obese edesba see opadcccs cogpos obbnus DoUnUsceds 6600 soDads sane oS 5S c00me0 BoKG Chpmngiom Wedls6 oss cecesae scoonabocc cons Sone rose Fon 6585 coos cobs ossasccgesos go00 S085 ID RONAGIONGD PEA nds cdan cado Hogo coed cone deen Soto oes sHoo SaeoeS peba obese SSao Gade PAAR AOI) Sasa eso6 60a adc5 conUDE Esco sens cece SeaG pope SsoTecseoeeene SO@IKEMOSEELS SAINGIIKOM ES. Sood nobo chek coes bode cess Sted cope cscs toss seen Sccce IDE SCLO Bie) Tim IEONMMINCD 5 Joscbade Saag bedateas seo eHsesdecascoads cons bosode Teranarile IRE WRG cose edse econ Sess esobsond coed open Gabe sso eosousad daddies e bade conese WEI paver WON GzqnoswN Sac doeicncs Sabolobss 646665856605 Saed cSce Soop Sess Sagboas5 DASH BLO AGINC® GNGED 5 coco 63cm chao chou Sado pone Sose So58 Nene Sha SaodooceSsoaso0" ILEOWEIS Commer CMEVTHAS . 250 6od5 dees escs cote sass bSoN sacs ceca sone sees cose Section from Watchemocket Cove to Riverside Halsey Farm section at Silver Spring --..--...-......-.-....-.--.---.------ IDSA TOSWONETS 10m SERVEROMIE 5555 Gono cegoeans aooo CHS ooga Séa0 2000 Sone cosboS SoODONSCON Hunts Mills section CONTENTS. CuHapreR V.—The Carboniferous strata—Continued, Coal Measures--—Continued. Beds north of the Tenmile River in Attleboro. ........---...---.----------------.----- Contact of red and gray beds, with local unconformity .----...--..-------- IRCUU AMIS Cos eoocbea. cane eecasaauoe cecoce soucqoo Hace coo abe baeEsecspeoossES IRM bay) Men ADM 5a Goa eso eacelbauede, paSSac.onSHoS SOMDONSSseeSdenodS Attleboroisymclin cheeses ese niecee emer ie eerie teelteae eee resecee TEND Leb)! TNwIh OG Ans oak4 Shee see set oe sen eusosocucescaesos seed senmeh asso os00 INGER Sadeon weccdasaabesn anoesesoanodbddduS abaeraDsocrs ospsedcuSocuDbonUD CO scsced cou cecoonsscusa che meuadso abs tocane sBaeebe.GaGSoH Sacd Ho seeane eco Bl akcepeiller bru gtap lanes iets estar se eiat tate erayo lee eebiaiaeneerereeetace IDA eA COMAONIG EA AKON) Sooo Hees dos oodbe He boc oebbo ened cess Hedacecoes cscs Popead Extension of the Coal Measures north and east of Taunton...-.-..---.-.---.---.---------- IDQGlnNenn CMACIENNEAE) so 5 coo Sune sseS asa eeESS Hede gess cocu cosabo seabed sstcod condensed sda IMEI A, MAD So OGd Gabeks dead She Seed Bes oue bho naS ooduod oHadcHeceHocusEEbEbaosacés lonavoteManst eldisectlonbsaes er eeseei seers aise ee ear eee aan IBGE NWA CURED ie Scope saEsbaCaNn weds Heae6 Code oaoD saesan eoabuS coo soan.sosecegsod Abington quadrangle.-...--- Seoeho adds canbe cosougsconoseGasa ones soba souccOleSEece soos ANA ENRIOM AMR NA scc5 Sac bo ode code pba bos boos cosa ecubedodeD boos obanonecccu.cedooscS WWodl Wecls Sesc6 sooseesegese cosdua bcos eseue soos bueceu nes sesoou conSnaogo cao OutcropspnypN Ontos eerie saree een yelalelemelereteale aie meee selniae \ivstomaconniay Iecleses) 565 aas5oeas codons sooacdo céoauds bond cocous soousawedd Beco SCOMMBNNS INCE. SSS se See GGachdc0 chon code00 vagece poUE bY coBbSeccuEse Go0cgDE Maumbonk wiaberwOrks SCCb1OMe 1.2 Directions in which the formation decreases in thickness WO 77S ? Possible exposures Fia. 11.—Map showing distribution of red sediments. of the Blackstone in Pawtucket. 4. A characteristic elongate narrow area extending along the northern margin of the main basin and traceable as far as the North River in the town of Hanover. This area is probably con- nected at the west with the succeeding. 5. The largest area of all, extend- ing from No. 1, near Sheldonville, northward and eastward to Braintree, forming the greater part of the strata in the Norfolk County Basin. There are exposures in (6) Attleboro and (7) Rehoboth, and one in (8) Norton, which may belong to a different horizon. I shall begin the account of these fields with the area along the northern border of the main basin. WAMSUTLA GROUP. 143 THE AREA ALONG THE NORTHERN BORDER. The area of reddish and chocolate-colored strata along the northern margin of the basin, from near Burnt Swamp Corner eastward, is consid- ered first for the reason that along this line there is indubitable evidence of the relative positions of the red and gray rocks. Throughout the extent of this northern margin the red conglomerates, sandstones, and slates occur at or near the base of the Carboniferous formation, or are separated from it by beds of arkose and gray quartzose conglomerates. The beds can be studied along the border in Wrentham about three-quarters of a mile north of the Shepardville reservoir, in two small hills lying west of the stream which comes in from the north. Immediately south of a small contact valley between the granitite and the Carboniferous beds of the border appear red sandstones and slates. The rock is pervaded by two sets of cleavage planes striking about in the line of the border, the dip of one being nearly vertical and that of the other into the granitic terrane at an anele of 70°. The attitude of the sedimentary beds is not very plainly exhibited. Limited exposures of banding indicate a strike parallel with the border and a southerly dip of from 25° to 30°. The outerops in the western knoll show red sandstones succeeded by greenish sandstone, which in turn is succeeded by more red sandstone. Near this locality an old mill- stone made out of a reddish conglomerate with small quartz pebbles was seen in 1894 built into the fence. The greenish sandstones just mentioned have a more extensive development in the North Attleboro area (p. 151). The red beds are well exposed on the southern face of Foolish Hill in Foxboro. They here dip steeply southward. The cleavage dips steeply northward. Thin bands of red slate may be seen intercalated between beds of whitish arkose. Red conglomerates with quartzite pebbles also occur. The thickness of the beds is difficult to obtain with accuracy, but it may be estimated at this point as upward of 1,000 feet. Red beds appear to the east near the contact, at some points conglomer- ates prevailing over sandstones. The thickness evidently diminishes toward the east, but exact measurements are wanting. The red color of the basal rocks also declines and becomes of a chocolate hue. The strata are rarely deep red east of Brockton, though deep-red slates occur northeast of Abington. In the eastern part of the field red conglomerates are no longer recognized. 144 GEOLOGY OF THE NARRAGANSETT BASIN. The relative paucity of granitic pebbles in the Wamsutta conglomer- ates along the northern border is evidently due to the previously mentioned condition of the granitite at the time deposition set in. Nowhere is there a sharper contrast between the arkose beds and the red shales than on the southern face of Foolish Hill. Bands of red shale here alternate with the arkose in a manner to show that the small particles of the shale brought with them their coloring matter from the seat of denudation, as Russell has argued in the case of the red beds of the Juratrias." The importation of the oxide of iron subsequent to deposition would have colored the arkoses and the shales alike. About a mile southwest of Whiteville, shown on the Dedham sheet, conglomerates oceur dipping gently southward. The quartzite pebbles of this rock are locally brecciated, and their surfaces exhibit a kneaded appear- ance on the matched faces, showing clearly that brecciation has taken place since deposition. The waterworn rounded surface of the original pebble can be readily traced. These dynamic phenomena indicate that the strata along this northern margin have never been under the pressure which has so profoundly acted upon the elongated conglomerate pebbles near Newport, Rhode Island. The shallowness of the waters—if indeed the deposits were made in a permanent water basin—over this area in Wamsutta time is shown by the current marks on sandstone layers between Whiteville and Easton, and by the coarseness of the sediments. The structure of the beds is everywhere comparatively simple, their dip being southerly beneath the carbonaceous strata which begin the Rhode Island Coal Measures. Their continuity is frequently interrupted by faults in the manner explained in the discussion of the boundary line from Burnt Swamp Corner eastward. Gray sandstones of the northern border —In the small hill near the border northwest of the Shepardville reservoir, in Wrentham, there are exposures of a brown- ish, sometimes greenish, fine-grained, rather massive rock, which under the microscope is seen to be composed of grains of clastic quartz and feldspar. This rock is at present considered as a member of the Wamsutta series, and, on account of its more extensive development a few miles southward, in North Attleboro, may be called the Attleboro sandstone. The outcrops ! Subaerial decay of rocks, by I. C. Russell: Bull. U.S. Geol. Survey No. 52, 1889, p. 56. WAMSUTTA GROUP. 145 along the northern border are of much importance in that they help to define the stratigraphic position of the rock. It is here interbedded with the red conglomerates and shales. Traces of this rock are seen at points eastward in the area under dis- cussion. Bowlders of a similar rock bestrew the hillside where the North River passes from the Carboniferous area into the region occupied by the eranitites. Here the sandstone is well bedded and alternates with bands of pebbles and slate. This variety of sandstone along the northern border is apparently much thinner than in North Attleboro. The probably volcanic origin of this rock, in the form of ash, is referred to in the account of the occurrences about North Attleboro. THE NORTH ATTLEBORO AREA. The most characteristic exposure of the Wamsutta group occurs as a horseshoe-shaped area, open on the north, in the towns of Wrentham and - NG cnet erat Fic. 12.—Geological section northward from Robinson Hill. North Attleboro, Massachusetts, and Cumberland, Rhode Island. The formation is a series of conglomerates, sandstones, shales, and calcareous beds with associated felsites, felsite breccias, felsite agglomerates, and diabases. A characteristic of the area is the very great thickness of conglomerates. Beginning on the northeast, the formation makes its appearance about a mile northeast of the village of North Attleboro, in Robinson Hill (see fig. 12), an eminence which overlooks the valley excavated in the softer strata of the overlying Coal Measures extending westward from Mansfield. 'The section MON XXxIII——10 146 GEOLOGY OF THE NARRAGANSETT BASIN. from this point to the northern border of the main basin seems to have the form of an overturned syncline, as shown in fig. 12. From Robinson Hill the red conglomerates, sandstones, and shales can be traced southward, with strikes conforming in direction to the general distribution of the formation, to Reservoir Pond, thence to Rattlesnake Hill and skirting the northern banks of Fourmile Brook. The formation thence trends in a southwesterly direction to South Attleboro. Good exposures may be seen in Red Rock Hill. Immediately west of Washington street and south of Allen road, the sandstones and conglomerates may be seen turning north-northwestward, whence they continue in that general direc- tion as a broad area of red rocks with occasional exposures as far north as the vicinity of Burnt Swamp Corner. A well-marked occurrence of these rocks is found between Abbots Run and Millers River. The stratigraphy of the area immediately west of the Blake Hill fault block in Plainville, and thence northward to the Sheldonville narrows, is imperfectly understood. About a mile north of the southwest corner of the block, the Wamsutta beds occur in a well. Between this locality and the Blake Hill schoolhouse, 1 mile southeast of Burnt Swamp Corner, gray Carboniferous beds appear in an unknown relation to the red beds above referred to. From the schoolhouse a strip of red conglomerates extends southwestward toward the main belt of these rocks, which here skirt the western border. The varying strikes and the repetition of isolated red and gray outcrops northward in the direction of Red Brush Hill render the structure of this region difficult of interpretation, since the gray beds may belong below or above the red beds, and criteria for the determination of their position are there absent. The boundary line drawn ufon the accompanying map (Pl. XVII) between the red and gray series in this region is therefore wholly conjectural. It is probable that the rocks are thrown into closed folds. Conglomerates—The conglomerates are composed mainly of waterworn pebbles of greenish quartzite. One pebble in the outerops in the valley of Abbots Run contained several Obolus shells, which, according to Walcott, are upper Cambrian. Granitic pebbles are common, and locally there is a large proportion of felsite. Stretching and fracturing of pebbles under the pressure of strong folding is evident from point to point im the more dis- turbed areas. It is probable that conglomerates occur on more than one “(G6BL) YOU 50 }sea Bulyoo 7 ‘s}asnyoesse) ‘O10Ga/}}y¥ YHON ‘Jaa.3s WIA ssl ‘AYIBDOF BIS JO} MBIA UI BjN1 JOO4 “SA}IWe}ed 40 s}sed snoaoeuogied BSuiAises sawsi0} ay} ‘spueq @}e1WO[SUOS YIM ajeys SNoJa}iUOqIeD Pay "dNOYUD VLLNSNVYM 40 dOYOLNO ONIYVAE-LNV Id Il “Id XXX HdVHOSONOW AZAYNS 1¥91901039 'S "Nn saris Pe iat ph Reena yy hee he a i uy WAMSUTTA GROUP. 147 horizon in this field, but on account of the intense folding, along with fault- ing, it is not satisfactorily determined to what extent the conglomerates are duplicated. Some of the felsitic conglomerates pass into agglomerates, and these into felsite breccias, well shown in the valley east of Oldtown. Sandstones—'["he sandstones of the area under discussion are of variable texture, becoming coarse and feldspathic and thus approaching arkose on one hand and grading into quartzites and shales by the separation of the quartz and decomposed feldspar on the other hand. The reddish quartzitic beds are well exposed on Robinson Hill and in general about the village of North Attleboro. Their detailed representation on the map accompanying this report has not been attempted. In the bend of the sandstone ridges at Red Rock Hill, Mr. H. T. Burr found rain imprints on the sandstone. snales—The shales, or often slaty argillaceous sediments, of the for- mation are well exposed in the valley between Reservoir Pond and Red Rock Hill. Other exposures occur east of the village of North Attleboro. Reservoir Pond appears to lie partly in a depression excavated along the line of strike of these beds. The shales are frequently interrupted by knobs and sills of felsite (see fig. 14). The beds contain flattened stems of calamites, as at Attleboro Falls, near Reservoir Pond, and east of Red Rock Hill. THE CENTRAL FALLS AREA. The Central Falls area is not well exposed. The best outcrops are near the High School in Central Falls. On the east, near the old post-road, con- glomerates occur with slaty beds in nearly vertical attitudes. In Pawtucket the beds are mostly red shales or slates at the same high angles. The breadth of the formation decreases rapidly southward along the strike. At the widest part it is as much as 1,000 feet. Its appearance in this part of the field is evidently owing to compressed anticlines and synelines in the highly inclined Carboniferous strata at the head of Narragansett Bay. The structural relations of this area to that in North Attleboro are best explained by an anticline arching over the conglomerates west of South Attleboro. This view also supposes that some of the Coal Measures, i. e., the Pawtucket shales, may be inferior in position to this southern extension of the red beds. 148 GEOLOGY OF THE NARRAGANSETT BASIN. THE PAWTUCKET AREA. Another small area south of the last, not more than a few yards in width, is exposed in the gorge of the Blackstone River, in the southern part of the city of Pawtucket. At this point the red slates are associated with green slates, recalling a similar association of red and green slaty beds at Pondville, in the Norfolk County Basin. Close foldmg appears also to be, in this locality, the explanation of the relations which these beds bear to the adjacent carbonaceous beds. This is the southernmost exposure of the red rocks known to me in the basin. Southward and west- ward in this latitude the red rocks disappear. At only one poimt on the Little Compton shore do red rocks appear at the surface outside of the areas named, and in this instance they are limited to a thin layer of red hematite in the coal-bearing section. The deposition of the carbonaceous series of the Coal Measures in this southern field preceded the incoming of Site of Site of N N Attleboro Fawtuchet a Fig, 13.—Diagram showing disappearance of Wamsutta group (Cw) in the Coal Measures (Cc). the red material from the north, and continued without interruption south of Pawtucket. RED BEDS IN ATTLEBORO, REHOBOTH, AND NORTON. These occurrences are fully considered elsewhere in this report. Rea- sons will be advanced in the following chapters for regarding at least the first two of these red beds as local deposits formed at different levels in the Coal Measures. The last-named area contains red shales with calamites in the drift a few rods south of the outcrop. NORFOLK COUNTY BASIN AREA. No detailed work was done in this basin during the present survey. As a result of a reconnaissance, fossils were found at Canton Junction, con- firming the views of Crosby and Barton as to the Carboniferous age of a part of the strata. The rocks closely resemble the red and gray beds along the northern margin of the main basin. Red beds largely predominate in all the exposures. A characteristic basal section has already been described at Pondville. The strata are almost everywhere inclined at very steep WAMSUTTA GROUP. 149 angles. While the section at Pondville indicates simple downfolding of the margin, the form of the basin and the distribution of beds along the border, particularly on the north, are suggestive of downfaulting of the beds in most parts of the basin. The strata are usually not so much meta- morphosed as those south of Pawtucket in the main basin. The occurrence of locally metamorphosed conglomerates at Morrills Station (see fig. 6, p- 120), on the Walpole and Wrentham Railroad, illustrates the effect of great pressure in producing the elongation of pebbles and in inducing secondary minerals. In this instance the rock has become very markedly sericitic and disintegrates rapidly. SOUTH ATTLEBORO LIMESTONE BED, This name has been chosen for the occurrence of nodular aggregations of calcite and amorphous carbonate of lime which are associated with the red shales of the Wamsutta or red rocks, and which are particularly well displayed in South Attleboro, in the southern base of the hill at the foot of which the town is situated. A section from the road northward up the hill is as follows: Section of the Wamsutta formation in South Attleboro, Massachusetts. Feet.. In: medushalesmconcewledusouthwardemer eres acces ss ae seve eee 6 0 HIN CKCOM LI OMOERALOG as eters tap iors Sie ti kee ar ays oes) she sie ele wie leo eisyayeve lates seem DCIS S 2 0 VES ale Ayelet asi reve eyciere erst eli Sealarcrajesleie< Se ah is Sa ay APS ere uray ea 6 IRROMOWG Wal ha esas GES Ga Soo SSO Sk re oe aoe ee rite a Asawa aetna 6 0 SMEs, ReGl’s sceGuaqodseneasoadsanbmooueEsous coHepaeseccucsescuEeacsae cube 10 0 CONGIOMOMID= 25 .cbacssascosodébsoobcnseesd sacsouscdddo sou sou oSHocEDobEss ay) SUNAIIES,, TAL, RRA? COWGIRL 5 ooebudaodes dgobae sosuceoDoomoeoomcsunoscusoase 119 0 SHINCIMOME, HEEL goeonssoosesdsdoudos Sooo succeouEdsosbads Coane ooDDCG SOsaaE 24 8 SWMIES, nol, joa; GOmMeCIGGl.. 54 55865555556osc00d00ned se ano aSS400000u0 5 Be (Felsite, reddish and irregular in thickness, exhibiting flow structure, 25 ft.) SIMHIICS, WOO. sso edcued nobsodesos pabcoc54s esosnN eaoun0 -coUGU USHoUO Coe as suauE 28 4 ediconslomerate icOarse) Peles aera ie 4 en leialelrel = re inet ele erica 60 0 SINAIVAS TREO Oe is ade ceoO Loa. BOs Boe tne en Een eno aharicc Cada HOO eos 60 0 (Diabase, amygdalar cavities on northern aspect, 15 ft.) Red shales, concealed northward, measured...... .....--..---.------.--..- 175 0 The limestone occupies irregular kidney-shaped cavities in the red shale, or is for a few inches of its thickness in the form of rude layers. Another mode of occurrence is as isolated nodular masses half an inch in diameter. These nodules are frequently elongated in the direction of the 150 GEOLOGY OF THE NARRAGANSETT BASIN. strike. Some of the larger masses, where weathered, show minute rounded apertures, marking closely set pits. Under the microscope, in thin section, a specimen of the amorphous limestone from this locality appeared as an aggregate of minute grains, oceasionally exhibiting large individual grains with distinct cleavage. Stratigraphically, the limestone is at this point relatively low down in the red series of rocks. The material can be traced westward and north- ward, by means of bowlders, in the same relative position on the east side of the valley of Abbots Run. Eastward and northward, limestone is again found on the place of Mr. Todd, near the old Powder House, in North Attleboro; but here the lime- stone is a mottled marble, which has been used for making quicklime. ‘The limestone bed here occurs in a thick section of sandstones and shales of red color, in no way identifiable with the section in South Attleboro. This occurrence is on a more northern line of outcrop than the former, and if stratigraphically connected with it, is to be explained by a fold such as is suggested by the general structure of this area. The irregularity of occurrence of the limestone in the different sections where it is exposed, together with its evident secondary origin, has led to no, dependence being placed upon it in the course of the survey as a plane of reference in the correlation of strata. ; Similar shaly limestone reappears in the Norfolk County Basin, near Canton Junction, Massachusetts, in a section described by me.’ A closely similar rock occurs in the Cambrian section in North Attleboro, where the limestone has evidently been formed from the remains of pteropods. These limestones were described by Prof. Edward Hitchcock, and a speci- men from the southwest part of Attleboro gave him the following analysis: * Analysis of limestone from Attleboro, Massachusetts. _ Per cent. Cal Ose a= ee Nea ae ie aa es ste ettewetcny Geant 94. 60 SOREN WON Salanstads odcbsa sunbscesacsdeods 5. 40 PNM SS ee ea Sescnoe dodobe shop cand eode saneDe 100. 00 Qiicklime sien 5s Ra eee eetscloeia bei Seveeere 52. 98 Specific gravity, 2. 71. ‘Am. Jour. Sci., 3d series, Vol. XLVIII, 1894, p. 147. ° Final Report on the Geology of Massachusetts, 1841, p. 80. WAMSUTTA GROUP. 151 The late Prof. T. Sterry Hunt suggested* that these limestones inter calated with red slates might correspond with those bands of limestone which are met with in similar red slates and sandstones at the base of the Carboniferous formation in Canada on the Bay of Chaleur and in New Brunswick. It is clear that the deposits lie near the base of the Car- boniferous in Massachusetts, but the evidence is as yet lacking that this section corresponds, in the sense of an exact correlation, with the base of the Carboniferous in the Canadian provinces. Economiéally, these limestone beds, so far as they have been seen in natural exposures, do not, in the presence of the larger and purer deposit in the neighboring crystalline region of Rhode Island, assume a commercial importance. As a local source of supply for individual uses, they will probably from time to time afford some employment. ATTLEBORO SANDSTONE. This is a fine-grained massive sandstone, varying from green to brown in color, the latter hue being due evidently to oxidation. The massive structure of this rock and the angularity of its particles of quartz and feldspar in many cases, as seen under the microscope, make it likely that it is to be regarded as a volcanic ash deposit, discharged from the vents which gave rise to the felsite flows of this northwestern corner of the basin. The most instructive exposures of this rock are in the town of North Attleboro. One may be seen just west of the water tower in the north- eastern part of the town. A more extensive outcrop is exposed south of Goat Rock and north of the Hoppin Hill granitic area. Other occurrences of this rock are to be seen embedded with the red series near Robinson Hill, north and east of the first-mentioned locality, and again in the same stratigraphic relation in the vicinity of Deantown, in Attleboro Township. The exposures along the northern margin of the basin, in the Franklin quadrangle, show the position of the deposit to be near the base of the Carboniferous formation. The quartz grains are there much coarser than in North Attleboro. The stratigraphic relations of the sandstone, where seen, indicate that ‘Am. Jour. Sci., 3d series, Vol. XVIII, 1854, p. 199. 152 GEOLOGY OF THE NARRAGANSETT BASIN. it is a member of the Wamsutta series. Fossils have not been found from which to determine the age of the beds independently. The texture and color of the rock, as well as its position and quantity, would make it fit for building stone but for the fact that it is quite devoid of those sets of joints or bedding planes on which the extraction of suitable blocks depends. IGNEOUS ASSOCIATES OF THE WAMSUTTA GROUP. One of the striking features of the Narragansett Basin is the localiza- tion of eruptive rocks in the area of the red strata of the Wamsutta group. Dikes occur, however, elsewhere in this region, in Lincoln, near Providence, and at the mouth of Narragansett Bay, marginal to the field. Diabase —An interrupted faulted series of narrow, partly altered diabase dikes can be traced from North Attleboro southward around the horseshoe fold of the Wamsutta group to Lanesville and thence northward toward Arnolds Mills. The diabase is usually erupted through red conglomerate, sometimes in the form of twin dikes with a large sliver or wedge of the country rock between. The upper surface of the diabase for a thickness ot from 1 to 3 or even more feet is commonly vesicular; sometimes the lower surface is amygdalar; but there is no evidence to show that the diabase flowed out as a contemporaneous sheet. These dikes are of variable widths from point to point where they appear, attaining thicknesses of from 20 to 50 feet. They frequently rise up as low black knobs, as between North Attleboro and Attleboro Falls, or appear as low bluffs, as on the east bank of Abbots Run and between Adamsdale and South Attleboro. For the most part they crop out along the outer limits of the circular area occupied by the red rocks. At a number of points these diabase knobs are so situated as to be available for supplies of road stone, for which purpose they are superior to any other rock in this district. The outcrops at Attleboro Falls are within sight of the railroad, and there is a mass adequate for local uses free above ground and now a hindrance to house building. The ledge on the Henry Guild place in Adamsdale and its continuation northward affords another source of supply the nearest locality of trap im workable quantity to the cities of Pawtucket and Providence. It would require a carriage of a mile to place the material on the cars of the New York, New Haven and Hartford Railroad at Adamsdale Station. To run a “HLNOS 43O LSV3 ONINOOT ‘GNNOYD3SYOS NI LSIYG TVIOVID ‘SLLASNHOVSSYW ‘OHYOSS1LLVY HLYON LV SAxIG ASvavVIG aa.lqav SHL 4O SdOYDLNO Al “1d INXXX Hd¥HYSONOW A3AYNS 1¥9I9N01039 "Ss “nN us Liens any WAMSUTTA GROUP. 153 spur of the railroad into the trap locality would necessitate building a bridge or trestle across Abbots Run. From a point half a mile north of the station, it would require about 4,000 feet of track to reach the ledge. Quartz-porphyries, felsites, and granophyres—Intimately associated with the red rocks of the Wamsutta group is a series of acid igneous rocks of felsitic and eranophyrie structure, the distribution of which is parallel with that of the diabase dikes just described, and, like the former, these rocks occur in knobs, whether true bosses or faulted and disjointed dike-like masses being not easily determined. In general they are limited to the horseshoe fold, and do not accompany the Wamsutta group eastward along the northern Fic. 14.—Section through felsite knob in Attleboro, Massachusetts. (See table below.) margin of the basin nor in the Norfolk County Basin beyond the narrows in Wrentham. The felsites are usually of a reddish color. A cross section (fig. 14) of one of these knobs south of Reservoir Pond illustrates the general character of the association with the Wamsutta group. The succession, beginning on the east, is: Section south of Reservoir Pond. Feet. Sandstone (red. pebbly,)andushales(red)) = 22.2.2) 285 ees ee 40 IDM OM pois oo oo SS NS OUTS 6 COR SER Sit eee tee et ONE ERER SA NG RE Sia Ato oe eae 40 DOIG 22 bd se was rer oROD Oba eit cs Oe Eee Deane SmaI e heme oP cene Gram One aaanor 10 Conailomemre 100 cacoucecusHeu desde sspapooapue us Sasaboudssod obo ouOESSE Osea 8 IB site, tin NewAeR® VINOD) coca coseouaneabodsan sogaDecanoDd ooucUdUoUCUCooDUasodeace 50 (Western contact not seen.) 154 GEOLOGY OF THE NARRAGANSETT BASIN. The felsites frequently occur higher up stratigraphically than the intruded diabases. The following scheme of arrangement of rocks at three localities will represent this fact: Stratigraphic relations of felsite and diabase at three localities. (LV, Z. 24.) (VII, D. 20.) (VII, B.7.) Red shale. q 2 ? ? g Felsite. Felsite. Felsite. Conglomerate. ? Conglomerate. Diabase. | Diabase. Diahase. Shale. Shale. Shale. Conglomerate. | Conglomerate. 9 g i Diabase. ? Conglomerate. 9 ? 9 Shale. 2 g Conglomerate. 9 This matching of short sections within 2 or 3 miles of each other, the first two being within half a mile, illustrates something of the constancy of occurrence of these igneous rocks. Regarded as a map, the bottom of the table is east, the top west. The interrogation marks indicate the places of concealed strata. The persistent failure of the western contact of the felsite is a noticeable feature, due to the erosion and concealment of softer material. The large felsite mass between the village of South Attleboro and Red Rock Hill causes the strata to separate in the manner of a tilted laccolith, but contacts have not been observed which verify the view that it is one. Flow structure, often attended with crumpling of the layers, is manifest in many outcrops of this rock. Beneath the massive flow of the felsite is a zone of the same rock, form- ing the matrix of an agglomerate, composed of rounded pebbles of felsite and quartz-porphyry, together with quartzite and occasional pieces of horn- blendic granitite. This lower bed is several feet thick. In South Attleboro there is exposed a bed having a thickness of more than 10 feet. The water- worn pebbles are evidently fragments caught up in a movement or flow of the felsite over earlier conglomerates. The groundmass of this agglomerate is porphyritic, with a plagioclase feldspar in every respect like that of the overlying mass. WAMSUTTA GROUP. 155 The eruptions of felsite in this field appear to have taken place some- time after the deposition of the first sediments of the Carboniferous section and before the laying down of the Coal Measures along the northern border. These members of the quartz-porpyhry family of igneous rocks are but outliers of more extensive eruptions of a closely related magma which is extensively intruded into the rocks of the Boston Basin or is found there as ancient flows. In that area the age of the eruptions is not precisely known. If the evidence from the area of the Wamsutta group in North Attleboro and the case in Plympton can be relied upon as evidence, it would point to the Carboniferous age of these eruptives in the vicinity of Boston, and probably to an epoch later than the lower Carboniferous proper. DIAMOND HILL QUARTZ MASS. Lying on the western border of the Wamsutta group, but apparently developed in these Carboniferous sediments and in the felsites, is the large mass of vein quartz known as Diamond Hill. The quartz occurs preyail- ingly in the vein form, with layer upon layer of divergent pyramidal-faced erystals. Locally the quartz is chaleedonic and white, earthy, opaline, the whole being evidently the product of hot springs following the decadence of igneous action in this area. Quartz veins having the same structure and habit penetrate the red sandstones of the Wamsutta group along the northern boundary in Wren- tham. This habit of crystallization has not been detected elsewhere in the basin, although extensive quartz masses occur at other points, as at Mount Hope, and in less abundance southward in the bay region. It is highly probable that the deposition of this quartz took place during Wamsutta time. WAMSUTTA VOLCANOES. The peculiar features of the Wamsutta series—the rapid thickening of the sandstones and conglomerates toward the northwest corner of the present area, the felsites with definite flow structure, the gray ash beds or Attleboro sandstone, the agglomerates of felsitic material, and the associated conglomer- ates composed in large part of felsite pebbles—all point to a voleano or volea- noes existing in this field in Carboniferous time. The known petrographic connection between the flow structure of felsites in extrusive masses and the coarser structure of typical granite-porphyries in stocks and dikes brings 156 GEOLOGY OF THE NARRAGANSETT BASIN. the phenomena of the Wamsutta series in North Attleboro and the under- lying terrane of schists with intrusive granite-porphyries in Cumberland into an interpretable relation. On the one hand, we have the effusive products of voleanic action; on the other hand, the underground conduits and rents filled with their equivalent portions of the magma. The same story is fairly derived from the Blue Hill region on the north side of the Norfolk County Basin. The beginning of sedimentation in this part of the Carboniferous land area appears clearly to have been accompanied by extensive acid eruptions. It is probable, as above noted, that the large felsite area about Boston was formed also in Wamsutta time. How much later the action continued can not be readily determined. The intrusion of pegmatitic granites in the southern arm of the Narragansett Basin, in the vicinity of Watsons Pier, together with the marked local meta- morphism of all the Carboniferous strata in that portion of the area, shows that voleanie action held on there later than in the northern fields, if it did Millers River Abbots fun Hoppin till WS W.S.W. E.N.E oy Fia. 15.—Geological section in the Millers River region. not altogether take place later than the deposition of the Carboniferous strata in this part of the continent. FOLDING OF THE WAMSUTTA GROUP. The folds of the strata of the red Wamsutta series in North Attleboro are the most complicated that have been found in the Narragansett Basin. The large horseshoe-shaped area of red rocks above described wraps around the older granitite and Cambrian rock of Hoppin Hill, so that the general structure is anticlinal; but the dips of the beds are now in many places inward toward the center, giving rise to an apparent synclinal structure. On the east, from the village of North Attleboro southward to South Attleboro, the dips of the red beds are mainly inward toward the Hoppin Hill area, until at the latter place they become very WAMSUTTA GROUP. ML - low, as in the nose of a broad shallow syncline (see fig. 15). On the western arm of the area the dips vary from east to west. Such marked inversion of strata warrants the explanation that the beds have been com- pressed inte the fan structure by the marginal collapse of a more or less quaquaversal anticline which formed over the Hoppin Hill inlier. It is owing to this extreme folding, together with the imperfection of the expo- sures by reason of glacial drift, that the region is so difficult of interpreta- tion. Northward, near Arnolds Mill, the apparent structure is indicated in the section, fig. 16. In the southern areas of red rocks in Pawtucket there is the most sat- isfactory reason for believing that the broad exposures of alternating red and gray rocks are due to close folding. This district, indeed, furnishes a clue to the structure of the nearly vertical beds southward along the W.S.W. Arnolds M/i// Fault Sarl \ T SS 7 - / t 7 Z Fig. 16.—Geological section in the Arnolds Mills region. western margin of the Narragansett Basin, in the Cranston beds, and in the equivalent Kingstown series, described by Dr. Foerste in another section of this monograph. This same field, showing the red and gray Carboniferous strata folded into isoclinal relations, affords strong evidence for believing that the Wam- sutta series, in the main basin at least, was not folded until the deposition of the Coal Measures, and that the entire thick section of sediments in the basin underwent plication after the period of deposition. All the facts from various points in the field support the view that there was but one period of elevation, and not two, as was formerly thought by Edward Hitchcock. There are a few disturbances along the northern margin in the Wamsutta area, which have been thought to indicate an upturning of the red series before the deposition of the Coal Measures in that section, but to my mind the evidence is not clearly demonstrative of this view. 158 GEOLOGY OF THE NARRAGANSETT BASIN, Several small faults exist in the North Attleboro area between Robin- son Hill and South Attleboro. These dislocations are indicated by the offset of diabase dikes along their line of strike, by the occurrence of beds in blocks, and also by the exposures in which the dislocation may be traced. In front of the house of Mr. H. Rhodes, about 14 miles northeast of South Attleboro, reddish sandstones are brought against the red slates, but this relation is probably due to local unconformity rather than to a fault. FLORA OF THE WAMSUTTA GROUP. So far as the observations of the present survey go, the sole fossils found in the red shales and sandstones of this series by Dr. Foerste and myself are a species of calamites and a cordaites. As a whole, the strata are prevailingly barren, a characteristic of red rocks everywhere. Enough of the flora is known, however, taken together with the stratigraphy, to warrant placing the beds in the Carboniferous section of the Narragansett Basin. This fully confirms the views of Crosby and Barton expressed in 1880. The geographical conditions under which the beds were laid down seem to have been incompatible with the accumulation of plant remains in the area of sedimentation, rather than that there is any difficulty in presery- ing fossils of this kind in red beds. In places abundant traces of calamites occur in the form of good impressions without a trace of Carbonaceous matter. In other localities the impressions of single stems are black with carbon, and had enough of these fragments been accumulated in one plane a black shale layer, if not a deposit of coal, must undoubtedly have resulted. There are reasons for believing that southward beyond the limits of the red beds plant remains were accumulating at this early stage in the Carboniferous of the Rhode Island area. The general absence of fossils in this series appears to have been due to a control exercised by the peculiar processes concerned in the deposition of the series itself. The pres- ence of quartz-porphyry pebbles along with masses of this rock and the related felsite, which appear to have come into their present relation to the strata before the deposition of the Coal Measures in this part of the field, suggests that volcanic action may have affected the formation of sediments in a way to be locally unfavorable to the growth and preservation of plants. THE CARBONIFEROUS STRATA. 159 COAL MEASURES. The Rhode Island Coal Measures, if we use this term to comprise all the horizons on which coal has been reported, include at one point or another in the basin all the strata from near the base to the great con- elomerate bed which occurs at the bottom of the Dighton group. The estimated thickness of this section is about 10,000 feet. There is reason to believe that the lowest members of this great thick- ness of sediments are, from Pawtucket southward, the time equivalents of the Wamsutta group. The relations of the Wamsutta series of red and green slates to the coal shales may be seen to advantage in the gorge of the Blackstone River at Pawtucket. The very considerable thickness of the beds between the basal arkoses and the conglomerates and the overlying Dighton group of conglomerates has rendered it possible to make certain divisions in this great middle section which have a geographical value and indicate at the same time lithological peculiarities. On these grounds four groups have been denominated, it not being satisfactorily determined whether the strata of the lower two beds are exactly equivalent or not. The supposed relations of these to the beds recognized by Dr. Foerste farther south are indicated in the table on page 184. In the following notes concerning the northern area local names will be employed, with such chronological limitations as present knowledge ot the field will permit CRANSTON BEDS: KINGSTOWN SERIES OF DR. FOERSTE. PROVIDENCE AREA. It is the general opinion of those who have examined the rocks west of Narragansett Bay in the vicinity of Providence that the strata of the Coal Measures are here nearer the base of the series than those which lie immediately on the east of Providence. This supposition is borne out by the structure of the sections which can be drawn for this region. The strata of this area from Pawtucket southward, to the limits of the Providence sheet, exhibit generally very steep dips prevailingly eastward. The strikes are generally east of north, being more persistent in the sand- 160 GEOLOGY OF THE NARRAGANSETT BASIN. stone beds than in the shales, the latter being very much crumpled and often striking east and west. The metamorphism of this belt allies it petrographically with the area southward in the lower part of Narragansett Bay. The sandy and pebbly beds, however, exhibit less dynamic metamorphism, but the shales above exhibit in a marked degree the development of new minerals which has resulted from this change. There are three well-marked north-south troughs about Providence in which the softer argillaceous beds occur, separated by more resistant arenaceous strata standing out as ridges. Beginning on the west, and next SESS SS CaN eins ey |Seekonk River . x Say Sooe= ae S > S ‘ SN XS Pw S ‘ ‘ Ris ‘ BES S ~. . Wasson ee < ST AR SS aN oe x x ‘ aa . N Be RO NNR Pea IRR Se Se XN ‘, ~ ‘ SS a Oy Le NN x 1 So RN SES Ten Mile Fiver ‘ ny vf WS SS Nol ge Parone Ginieeciae dee ee isos ‘’ s 1 ae: S ~ -- WY Me EOS Nuucicine . SM So. ‘ \ 1 AA TSS me cS S55 Medias ‘ \ SSNs Se ~o5 \ ‘ 1 4 Naw SK ek ~ s ‘ t OS ‘ SS ~- WwW \ 4 Sh Q 25 ~ \ \ : mm RNG See ‘ 1 ’ 4 ‘ / Lane ny ay u u ¢ yu Aescnit is WW Fic. 17.—Hypothetical geological section east aud west through Providence, Rhode Island, showing supposed relations of Cranston and Tenmile River beds. the escarpment which marks the crystalline and igneous border, there is the depression between it and Sockanosset, Rocky, Sky High, Bradley, and Windmill hills. The structure and character of the strata occupying this depression can be inferred only from isolated observations, mainly in the “dugway” in the southwestern part of Cranston, where the basal beds of the Carboniferous cling to the escarpment in a recess. The next trough on the east, which opens out into the bay south of Providence, is very thoroughly filled in with glacial sand plains. The occurrence of conglom- erates toward the south and the evidence from borings in the cy of Providence are the sole indications of the stratigraphy. RHODE ISLAND COAL MEASURES. 161 The coal from Cranston afforded F. A. Gooch the following analvsis:' Analysis of coal from Cranston, Rhode Island. | Percent. | | er VWI Be Goones Soa pee ans Nee esa ane Sameera Sons cece | 0.24 | Wiolatilepm ait terse stan ee ee ee ere | 4.49 | Mix Cdl Carbon seme aaeae eee eee eee 82. 20 AGN paonidose ssop soae Sen ones cees Soae SoSe BH aebane 13.07 | MO Las rae ae pate ee apa eR NA, 100. 00 SOU NE. cod Boobie sk Pak aseaese eddboedsenSeosance 0. 34 Specific gravity, 2.209 at 150°. These troughs appear to be mainly underlain by coal-bearing shales. The Sockanosset mine in Cranston comes in this section. In the valley north of Providence the shales crop out in a cut in the Old Colony Railroad. A well sunk in Butler street, corner of Bassett street, in 1895, penetrated the Coal Measures. Samples of the materials brought up from certain depths were furnished the Survey, through Mr. N. H. Darton, by Mr. C. A. Ray, of East Providence, Rhode Island. The following table sets forth the data obtained from this well. Record of well sunk in Providence, Rhode Island, in 1895. Depth in feet. Schist, soft, black, graphitic; with water turning to graphitic mud, somewhat LOGSenibuystornlubricatin op WE pOSCSie seen see ee ee eee 126 Schist, micaceous, carbonaceous, carrying large cubical iron pyrites........... 176 SOM Siy CAH OODACOOUS soscoscccces season cee sdgcben suSsoS Sos pobuosyeSacosusee 309 SNS, SIONS ooscaccasdgoooedasosuodiesos doggsa sods see sabonosbadscs ses 341 (Cink, OF ING IAIMONO IMG SENNO MON). Jose des cete sen bos cesbacccccucosuesocess 352. 5, Schist, graphitic, with fragments of vein quartz...........-................ 419 Coal, anthracitic; very light, with small cubic fracture and some irregular patchestotdullublackicaT boner presence eee eee eee eee eee 460 Coal, cut by veins of quartz, subfibrous near walls .......................... 475 Coal, with small cubical fracture and more of the dull lusterless carbon, about. 477 Schist, heavy, black, graphitic, pyritiferous, about......--..-.........-...-.. 477 Schist, fine micaceous, pyritiferous in layers ..........-..-...---.---..-..--- 492 ‘Report of work done in the Washington laboratory during the fiscal year 1883-84: Bull. U. S. Geol. Survey No. 9, 1884, p. 18. MON XXXIII 11 162 GEOLOGY OF THE NARRAGANSETT BASIN. Pawtucket shales.—Still farther northward in Pawtucket the shales are well exposed in the banks of the Blackstone River on Division street, and at Valley Falls they are exploited in a graphite mine. The best natural exposure is along the eastward bend of the Black- stone River between Central Falls and Valley Falls, where, on the south bank of the river, a section of bluish and black carbonaceous shales, with fossils, is thrown into a broken fold with minor contortions (see fig. 18).: The strike here is approximately east and west, and the dips are steep, mainly 80° N. The beds evidently overlie the grits and red series half a mile south. The slate layers contain distorted and disjointed fragments of plants. Further evidence of the movement which the rock has under- Fig. 18.—Folded and faulted Carboniferous shales on the Blackstone River at Pawtucket, Rhode Island. (Looking east.) gone is shown in minute joimts, in antiparallel sets, accompanying small puckerings of the slate. Along each joint plane there has been a minute fault movement of the normal kind. The thickness of the beds included under the term Pawtucket shales, if we place here all the soft beds in the troughs so far described, can not be safely stated. If the structure about Providence is due to the duplication of beds by overturned folds, as indicated in the theoretical section (fig. 17, p- 160), and since there are at least 3,500 feet of beds between the sandstones of the western or Sockanosset ridge and the base or western boundary, the apparently great thickness of beds in the other valleys may be readily ‘LSSM ONIMOOT ‘VLVYLS SNOYSSINOSUYYS 4O 3DaIy Q3LVIDV19 ¥ ‘GNVIq1SI AGOHY 'SONAGIAOYd ‘WHIH ANDOY A "1d INIXXX Hd VHSONOW 3 : : AJAYNS 1V91901039 ‘Ss ‘nN ‘had Ah aM be RHODE ISLAND COAL MEASURES. 163 explained. How much of this section is to be allotted to the shales alone is not known. Sockanosset sandstones —T'he ridges in this area, including the ridge in the Kast Side area, are evidently due to the presence of sandstones and con- glomeratic beds. They are well exposed on Sockanosset ridge east and west of the reservoir. They are members of the Kingstown series of Dr. Foerste. The shales are carried well up on the eastern flanks of these hills. Pl. V represents a side view of Rocky Hill, showing the glaciated northern slope. EAST SIDE AREA IN PROVICENCE, Knowledge of the stratigraphy of this area is limited to a few out- crops and to occasional borings, the latter of which have been recorded by the Providence Franklin Society." The rocks consist of sandstones, shales, and pebbly beds, exhibiting the aspects of metamorphism commonly found farther south at Sockanosset and in the lower bay region. The schists are frequently highly carbonaceous. The rock reported to have been taken from the ledge on which Roger Williams landed is a black metamorphic shale, or ilmenite-schist, soft and readily falling to pieces under abrasion. his rock evidently gives rise to the depression in which the Providence and Seekonk rivers run. The attitude of the strata in this area is exhibited in the outcrop opposite No. 75 East George street, near Gano street. There are here about 38 feet of slates with arenaceous and pebbly beds, all showing signs of crumpling under great pressure and standing at angles of dip as high as 80°. The beds strike N. 25° K. magnetic (N. 14° E.), dipping in one place E., in another W. The fine conglomerates contain quartz and quartzite pebbles. There is a pronounced cleavage, for the most part striking N. 65° W. magnetic (N. 76° W.), and dipping about 60° N. This secondary structure seems generally to have been taken by the inexpert for strati- fication. Similar exposures exist on the hill to the west. Rock is also reported to have been struck in borings at a few feet from the surface and in making excavations for the reservoir. Coal is said to have been met with on Benefit street south of Church and Stair streets. On the land of the Swan Point Cemetery, between Swan Point road and Blackstone boulevard, is a small outcrop of massive grayish sandstone, 1 Geology of Rhode Island, 1887, Addenda, pp. 129-130, 1888. 164 GEOLOGY OF THE NARRAGANSETT BASIN. such as is characteristic of the Coal Measures on the east side of Providence River. The rock exhibits a fissile structure, striking N. 25° EK. magnetic (N. 14° E.) and dipping 60° E. These figures give also, I believe, the approximate attitude of the stratum TENMILE RIVER BEDS. The Coal Measures east of the Providence and Seekonk rivers as far as the eastern bank of the Tenmile River afford characteristic exposures of slightly altered sandstone, pebbly beds, and shales. Coal has been found in the bed of Tenmile River. These strata may for reference be denoted as the Tenmile River beds. The essential features of this horizon are set forth in the following description of localities. If the beds on the west side of the Seekonk and Providence rivers are, as the local structures indicate, in an anticlinal relation with those on the east side of those streams, the meta- morphosed shales and sandstone of the Cranston series are the equiva- lent of the Tenmile River beds. For the present it seems best to consider the beds as two geographical groups. The presence of the Odontopteris flora and the insect fauna in the Tenmile River beds allies them, it should be noted, with the metamorphosed strata at Pawtucket and Sockanosset, and favors the idea that the two series are essentially at the same horizon, though it is probable that the Tenmile beds do not, as does the Cranston series, run downward to the base of the Coal Measures. (See fig. 17, p. 160.) LEBANON MILLS EXPOSURE. A low outcrop in which there isa small quarry occurs on the west bank of the Tenmile River at Lebanon Mills. The beds are conglomerates, sandstones, and slaty shales, striking N. 48° E. and dipping 70° S. One of the slaty layers contains worm burrows and plant stems (Sigillaria, Cala- mites), and the beds have here and there a reddish hue. The beds clearly underlie those on the east bank of the river. EAST PROVIDENCE AREA. Very good exposures occur in the southern part of the town of East Providence, Rhode Island, in quarries near Leonards Corners, and particu- larly along the shore of Narragansett Bay from Watchemocket Cove south- ward to near Sabins Point. The strata in this area are in marked contrast to the exposures on the west side of the Seekonk and Providence rivers, RHODE ISLAND COAL MBASURBES. 165 3 as regards both attitude and alteration. They not only lie in less disturbed positions, but they preserve to a much greater degree their original clastic texture, and fossils are of frequent occurrence in them. An account of the more typical exposures as they now exist follows: Leonards Corner quarries —In the southeastern triangle formed by the roads, at an elevation of about 100 feet above the sea, is an exposure of pebbly sandstone on the site of a rock crusher. The strike here is about east-west and the dip very gently to the south. An unidentifiable fossil tree, over 9 feet in length and from 6 to 8 inches in diameter, lies prostrate in the bed- ding, with its major axis east-west. A half mile east of the outcrop just described, about 25 feet of the coarse pebbly sandstone of the Carboniferous are exposed in Mr. John McCormick’s quarry. The beds are massive, essentially horizontal, with traces of coaly shales and coal, the last Glacial drift Se Se oe = Cee eS mostly marking the sites of single plants. The following plants were found: Calamites suckovii, in large, well-pre- served forms, showing inner markings. One large specimen, somewhat flattened, carbonate of lime. This stem lay nearly east-west, as did others in the same quarry, but the plants are disseminated and occur at no particular level, indicating the occasional drifting in of floating trees and the rapid accumulation of the sands and pebbles. Sigillaria? Long, slightly tapering, flattened stems, with longitudinal striations, but without cross markings, occur in this section, usually pre- served as internal casts in sandstone. They may be ill-preserved calamites. In the rubbish in the bottcm of the quarry, but evidently transported, were fragments of shale with raindrop impressions. The sandstone beds are traversed by a fault striking N. 44° W., with a hade of 10° S., and the well-marked slickensides have a uniform pitch on the exposed wall of 55° NW. This dislocation can not be of any consider- able extent, for the same sandstones lie on both sides of the plane of divi- sion. Another set of divisional planes, in the form of very close-set joints, striking N. 46° E., divides the sandstone along a belt of variable width into 166 GEOLOGY OF THE NARRAGANSETT BASIN. blocks too small for building purposes. (See fig. 19.) This zone of jointed rock widens from not more than 2 feet at the present surface to 10 or 12 feet at a depth of 20 feet. Section from Watchemocket Cove to Riverside —The rocks which appear in the quar- ries above described come to the seashore in bold cliffs between Watche- mocket Cove and Riverside, and in a few places the natural section has been made clearer by railway cuts. About 100 feet in thickness of Carbon- iferous sandstones, conglomerates, and shales are exposed along this section, in the form of a broad, flat syncline from Watchemocket Cove to near Pom- ham Rock, where the strata become vertical and are much disturbed, at one point the sandstone beds having been reduced to breccia. The strata just south of Silver Spring form terraces overlooking the bay. Northeastward from Pomham Rock and Riverside the same strata are seen inland in the three ridges indicated on the topographic map. In the eastern one of these long, low ridges, the sandy conglomerates dip northwestward at a very low angle, but the strata in the westernmost of the ridges dip steeply east, being along the line of the Pomham anticline. Northeastward, at a point about a mile due east from Vue de I’ Eau, the strata turn more to the eastward, as if in the canoe end of a syncline. (See fig. 20.) A BIC 0 E F NE Fie. 20.—Geological section from Watchemocket Cove to Riverside, Rhode Island, showing the attitude of the Carbonifer- ous strata. A, Kettle Point; B, Squantum; C, Silver Spring; D, Pomham Rock; E, Riverside; F, Outcrop near Sherman Station. South of Riverside the rocks are not well exposed. The details of stratigraphy along this shore are sufficiently illustrated in the following notes: Halsey Farm section at Silver Spring—A few rods south of Silver Spring Station the following section was measured in the bluff at Halsey Farm: Section in bluff near Silver Spring Station, Rhode Island. Feet. Sandstone andiconglomeratel(abitop)eemes see eee eae eae eee eee eee eeeeeeees 40 Conglomerate with pebbles of quartzite and granite........................-.-. 6 Sandstone (to bottom).-........-..........- dilate niles S12 Sin) hls aati eRN Shay f eC ESE ee ae 4 These strata are approximately horizontal, but farther east they dip : eastwardly, and westward across the railroad track they dip as high as ‘“HLYON ONIMOOT ‘GNVISI SGOHY 'ONIYdS YSATIS LV SLIUD GNV SANOLSGNYS SNOYSSINOgYVO SNiddIG-dY¥MLSV3 1A ‘1d NIX*X HdVHSONOW AJAYNS 1WS1I901039 'S “Nn sie RHODE ISLAND COAL MBASURES. 167 45° KE. In the railway cut the same series of strata show a north-south vertical fault plane, the slickensides of which are horizontal. There is Sea Jeve/ Fic. 21.—Geological section through rocky islets at Halsey Farm, Silver Spring. a, the rocky head shown in Pl. VI; R. R., the railroad. present a coarse slaty cleavage, but it is not a constant feature. The joint planes display great feathery surfaces of fracture, the divergent lines of which indicate the direction of splitting; this sometimes is upward or downward, but very frequently in a horizontal direction, the plane being vertical. With certain precautions, the dip of massive beds can be obtained by observing the inclination of the axes of these feather fractures. The Joint planes frequently die out with a convex front, the periphery being cast into concentric flexures of conchoidal fracture, often measuring an inch from trough to crest. These planes of fracture exhibit splitting figures having a length of at least 6 feet from the rather indistinct point of origin to the sharply incised marginal rugosities.! A few rods farther south, but north of Pomham Rock, is a small rocky headland, composed of two distinct ridges, in which the following section was shown, dipping 45° E., the same rocks reappearing in the islets north- ward by the Silver Spring shore. WwW Sea eve! ‘ Section in rocky headland near Silver Spring Station, Rhode Island. Feet. Ge, [SVEN (CHINO) D) SSRN ceagR a hh eat ayo aR a Re AR aghast 15 Glo. CONES 3 Glico tile erence! apie ei ceteciaay SRENP nee gr Cetera RRs Ue ie (ts SO OES en Sa 15 CR Slates wpartlyscovered piesa eaten. seuss scl 8 iene! | Al LUG ye ae eee ee yy 25 b. Grits and sandstones, with pebbles, isolated, and in bands and pocketsieeeneea: 15 a. Slates with sandy layers, showing local unconformity to b, due to contempo- raneous erosion; plant stems occur, and the upper portion of tie bed is car- bonaceous; cross bedding very marked; exposed above high-tide mark... .. 6 ‘For a detailed description of this type of fractures, see paper “On the fracture system of joints, ate.,” by the author: Proc. Boston Soe. Nat. Hist., Vol. XXVII, 1896, pp. 163-183. 168 GEOLOGY OF THE NARRAGANSETT BASIN. Fossils North of the station black shales contain impressions of Sphe- nophyllum schlotheimii, both alone and with “SLLASNHOVSSVW 'WVHLNSYM 'ASTIVA ATTIANIVId A le, IX Td INIXXX HdVHSONOW ASAYNS WW9INO1039 *s *n pa a i P is nt rie ie ‘; RHOD#H ISLAND COAL MEASURES. 181 Section of Goat Rock Cliff—Continued. Feet. Inches. Shalexdark-islaty,a Mere layers szsreces se vee a eee cece Sees ee eS ee 32 Sand Stomergoravgperiee teers atcha varia eae or eM AT Pure he eshte tesa oats 5.5 Shales withutossilsvoradinontorsandstoneee sss sy sneer oie eee 4 SMCS, SEN: S600 bear eS SE aoe enOAne A ME generat dia names Seas 6.5 Slate mma epee ear siht nose oe none stems Met mee Se ers & SONS alana . 75 Sand Stone pawl an Ge OT Avan OC kerysers suse -y0s 9 erate vey eee eee ee 4.5 (Conhs, rerhy gael (NGA bos elena Sea eae era ee ar AU ee ees 9 Sandstone, gray, with plant stems, and traces of fine-grained dark slate .- . 2.5 Sandstone; subslaty, with plant stems o---.2.--2.. 2.2.2. .5222--255--2---- 1 Sand sconessnmesorain ednson aivasreet epet ees lsearsye 2 eee eee 6 Sngike, Glavak, Slkniiy, MRCS ssocer sauesicodouduaanous sssouusbcoussenbasososs 25 ATG SLOM eon areas oars see Sy ataren eee, eon NE CN SR Rave Canina ate 3 Shale, dark reddish and slaty, with plant stems ..........--....-.---.-.. 75 Conglomerate roray, andeoritty, vather time: s2 22-2 2-2 asec oae oe 2.5 Shalewblacksanduslatyanwiathy plambistemses 222-2 so scs. 2 is eels eer 8.5 Sandstone, fine grained, dark gray, and in places gritty .................- .4 Shalesidankwandeslatycevee etter cro cass cieewslersicel olsaye 2 svete e ceceaiae, SNITONAS OYOS3ILLY 3HL 4O SIXY SHL NI SALVYSWOTDNOD NOLHSIG 3SYVOO 3H1L 4O G39 WVOIdAL WX "Id IN HdVHDONOW AFAYNS 1V9I901039 *S “nN ‘dayaueip ul saydul g 0} g 's “ANITONAS Td ‘IIIXx HdVH9ONOW AaAYNS 1V91901039 * Sas) ae FeV te as DIGHTON CONGLOMERATES. 185 In this northern part of the basin the several exposures of conglomerate referred to the Dighton group lie in the inner or upper part of synclines. This is true of the Great Rock area in Rehoboth, whence the rocks extend b) eastward to ‘“‘Rocky Woods,” near Taunton. Another, and perhaps the best area, is that of the Dighton syncline, extending from Dighton into Swansea. Another well-defined syncline in which these beds are found forms Ides Hill, west of Attleboro village. The coarse conglomerates at Purgatory and Paradise rocks, in synclines near Newport, resemble the rocks of this horizon. The outcrops of coarse conglomerates at Swansea Factory and imme- diately west appear locally to strike northwest and dip north, indicating either that the great syncline is overturned southward or that there is here a local folding along the northern side of the major synclinal fold. Outcrops are too few to verify either hypothesis, but the high inclination of the observed strata southward below the Dighton group shows that the beds on this northern side of the synclinal axis stand at much higher angles than do those on the southern side. The Great Meadow Hill syncline is nearly symmetrical, but the Attleboro syncline on the north is unsymmetrical, with vertical dips on the south side of the axis. The Dighton conglomerate is composed mainly of grayish and green- ish quartzite pebbles in the southern areas; toward the north, as in the Attleboro area, it is equally rich in granitic pebbles. The amount of quartzite in this group must represent several hundred feet of strata stripped off the adjacent country in Carboniferous times. Many of the pebbles are fossiliferous, carrying the upper Cambrian fauna already described. The pebbles vary in size from a fraction of an inch to rounded waterworn cobbles a foot in diameter. The reduction to spheroidal shapes apparently indicates their passage through the surf line on a beach. (See 12, SOUL) In many sections the pebbles are packed together with the pellmell structure of glacial till; the paste is often earthy and ferruginous, and when slightly attacked by weathering allows the pebbles to roll out; in other sections pebbles and paste are thoroughly cemented, so that the rock breaks up only along joints. Now and then a pebble shows a joint recess where the rolling action did not continue long enough to reduce it to the form characteristic 186 GEOLOGY OF THE NARRAGANSBIT BASIN. of wear on a beach. The frequeney with which this occurs in the larger pebbles suggests that when submitted to the action of the waves the bits were angular joint blocks, such as quartzites afford when broken out of a elif (See photograph of one of these joimt niches in pebbles, PI. XTY.) Here and there an indented pebble may be seen. The Dighton group of conglomerates being the highest member in this basin, the areas in which it oceurs are, owing to the deep erosion of the basin, somewhat removed from the present margin. The distance is gen- erally from 3 to + miles. The topography of these conglomerate areas is bolder and more rugged than that of the other rocks in the basin outside of the Wamsutta series. The formation abounds in rounded, bare, rocky knobs, with steep vertical blutts facing outward trom the synelinal axis over the area of the Seekonk sandstones, again overlooking recesses in the formation itself. Long rocky ridges also abound, as in Dighton, Taunton, and Attleboro, now generally given over to woods on account of the scarcity and infertility of the soil and the general unsuitableness of the surface to agriculture. The conglomerate masses attain elevations of 150 to 180 feet above sea level, or of SO to 100 feet above the surrounding level. In Swansea the conglomerate ridges rise to 160 feet; in Dighton, to 180; and in Attle- boro, also to 180. Near Taunton, the Rocky Woods attain an elevation of 160 feet. This level, indicated by the elevation of the conglomerate ridges, is somewhere near that of the Jura-Cretaceous peneplain were it extended eastwardly over the Carboniterous area. The excavation of the strata below this level must be attributed to erosion in the Tertiary period. These conglomerate areas contain the headwaters of numerous brooks, but several of the larger streams in the southern part of the field flow across them, evidently from original courses which have been superposed on these hard rocks. It remains to be determined whether there is an unconformity between the Dighton conglomerates and the subjacent Seekonk group. It is to be expected that even within the same geological period such discordances would exist where currents were developed strong enough to urge cobbles a foot or more in diameter out over an alluvial plain like that formed of the Coal Measures. The original thickness of the group is also a matter for further investigation. Were there higher Coal Measures in this area? And NOGRAPH Xx MON LOGICAL SURVEY S$. GEO u. 4290/4 3/NB} [1H e42/q JO PUaLUdJeOSa Papoom P:eMo} JsaMU}NOs SulyOo| ‘uO!ze}s peos|ie) WWOI} Js9MYPOU-YpOU alW e yo SYyNo}-aasy | SLLASNHOVSSYW 'STTIANIVId 'SANOLSGNYS SNOYSSINOSYVS TOILYSA AX "d_ IIIXXX HdVHSONOW AJAYNS 1VOIDNO1039 "Ss “nN COAL MEASURES OF THE DEDHAM QUADRANGLE. 187 did Permian or later strata overlie them? There is a chance that in the center of some one of these synclinal areas higher beds than have here been recognized may be discovered. It is indeed possible that the whole of the Dighton series is of Permian age. The contemporaneous flora and fauna of the conglomerate are as yet practically unknown. The brachiopods and worm burrows reported in the quartzite pebbles belong to the upper Cambrian fauna. (See p. 109.) EXTENSION OF THE COAL MEASURES NORTH AND EAST OF TAUNTON. Having described a typical area of the Coal Measures and the over- lying conglomerates in a part of the basin where evidence of their structural relations can be had, it is now purposed to describe the eastern extension of these rocks, where the structure is less well understood. For convenience, the order of presentation which is suggested by the mapping of this portion of the field in sheets of the atlas folio will be followed, for the reason that within the limits of these maps, comprising the Dedham, Abington, Middle- boro, and a part of the Taunton quadrangles, the exposures of strata are too few in number and extent to permit any systematic account of the stratig- raphy. These rocks have been described with more fullness than their importance apparently deserves, partly for the reason that they have not been heretofore described, and partly because they are the sole indications of the under geology of the eastern part of the Carboniferous field. DEDHAM QUADRANGLE. The Carboniferous rocks of the main basin cover the larger part of the southern third of this quadrangle. After we pass southward and ~ geologically above the rocks immediately along the border, outcrops are too few to give more than a very general view of the stratigraphy. The Coal Measures are present in Mansfield and West Bridgewater, and probably underlie the intermediate towns. The surface, outside of the glacial sand plains, is strewn with flagey micaceous and feldspathic sand- stones suggesting arkoses, which agree in character with some of the out- crops. A few conglomerate bowlders of the gray series occur, but never in the abundance which characterizes the proximity of the coarse Dighton group in other parts of the field. There is also absent the hilly and rough- ened topography which accompanies these latter beds when they occur in 188 GEOLOGY OF THE NARRAGANSETT BASIN. synclinal areas, and it is evident that these upper portions of the Carbon- iferous have disappeared by erosion from this northern field. The rela- tively gentle dips along this margin, together with the observed great thickness of the formation where fully developed, would carry the outcrop of the uppermost beds several miles south of the border and out of the Dedham quadrangle. The structure of the strata in this area, so far as it can be made out from observed outcrops, is mainly synclinal. The axis of this fold passes approximately through Mansfield Junction and South Easton; or, in general terms, lies at a distance of from 2 to 3 miles from the northern border. The trough is broad and shallow toward Brockton, but its sides steepen westward toward Mansfield, and between North Attleboro and the border it is much compressed, and the folded strata are finally lost to view beneath the block at Blake Hill. Its general features in the Mansfield area are shown in fig. 27,0n p. 190. ‘The following observations set forth the evidence in typical areas, about Mansfield and Bridgewater: MANSFIELD AREA. There are no surface exposures in the immediate vicinity of the West Mansfield coal mines, the rock having been found in digging a well. The lowest strata of the Carboniferous appear nearly 4 miles north of the coal mines, dipping gently off to the south from the hornblendic granitite of the Wrentham-Hingham uplift. The basal arkoses and grits, described with the Wamsutta series (pp. 135-139), form conspicuous ledges on the southern face of Foolish Hill, nm Foxboro. The Wamsutta series has here a possible thickness of 1,000 feet. It is succeeded on the south by quartz pebble and quartzite conglomerates and gray sandstones, forming glaciated ledges scarcely above the general surface of the glacial drift. Southward from Foolish Hill toward Mansfield Junction, beds of sandstone and conglom- erates appear, dipping about 25° 8. A roche moutonnée gives the follow- ing section from the top: Section of a roche moutonnée in the Mansfield area. Feet. In 5. Sandstone, with layers of slate pebble conglomerate ..........-..-.....--- 6 6 ARISEN KIN Eo wos nees.s oo be ot aspecSseeena boone sons SobeasuscloocHesb ence 3.6 ou CongiomerateswithyslateRpelb]eSieee see se se eee eee eee ee i @ Di Sandstone ee es see es eS A E AiSe His Jase Se ca pepe ene arate EN eee eee 5 0 1, Comllonaverenie, WHIS® WOE SAIN socs0c5ssscs0scsos5eoe5saccsccssasscouse cas: 10 0 ($681) SeMYYOU Sulyoo> yye] a4} UO ada} aUO}s Pulyeq aur] SBAOIE) U} AU! [BOD PjO $0 B}IS ‘saiNsea|Ay [BOD AY} 18AO Bulaaoa WE; jeloR/S Buimoys “SLLASNHOVSSYW ‘GISI4SSNVIW LSSM LV 30V4YNS 4O MIA TVYSNSO AJAYNS WVOINO103D “Ss “"N VAX “Id IIIXXX HdVHSONOW COAL MEASURES OF THE DEDHAM QUADRANGLE. 189 These beds dip to the 8. 80°; the cleavage dips N.50°. The exposure is noteworthy in exhibiting preexisting dark slates, broken up and deposited at this time. The slate fragments are angular and conspicuous elements in the layers in which they occur. They vary in length from 3 to 4 inches and in thickness from 1 to 2 inches. The attitude of the fragments and the unruptured state of the stratum, except for joints and cleavage, preclude the formation of the slate fragments by the disruption in post-Carboniferous times of an original argillaceous layer. For similar reasons, the fragments are not to be regarded as contemporaneous pockets of argillaceous sedi- ments. In the absence of contained fossils or other evidence of the age of these pebbles, there is doubt whether they are fragments of the subjacent Carboniferous shales or are detached pieces of the dark slates of middle Cambrian age, remnants of which occur at Braintree, in the Boston Basin. The not infrequent occurrence of signs of contemporaneous erosion in the Carboniferous beds in the basin leads me to conclude that the con- glomerates are of the class called ‘tintraformational” by Walcott. I have already described a limited occurrence of this kind at the contact of red and gray beds in Attleboro. North and east of the junction at Mansfield occur a few outcrops of conglomerate with small pebbles and associated sandstones. At the junction are two exposures of grayish feldspathic sand- stone—massive beds, like the typical sandstone ridges of the Seekonk formation. The knob west of the railroad carries the flattened impression of a large tree, and the rock in the railroad cut is much shattered. One and a half miles south of the Junction is a locality where coal was formerly mined (see Pl. XVI). In the absence of surface exposures, and because of the abandonment of the old shafts, it is impossible to get other data concerning the structure at this locality than those furnished by the records of earlier surveys and by one recent boring. From the Massachu- setts report” it would appear that the beds here strike NW.-SE. and dip NE. from 30° to 35°, or as high as 45°, and in another place that the strike of the beds is NE.-SW.; but the observation of C. T. Jackson,’ that the “strata between which the coal beds are included run quite uniformly 1¢. D. Walcott: Bull. Geol. Soc. Am., Vol. V, 1894, pp. 191-198; Bull. U. S. Geol. Survey No. 154, 1896, pp. 34-40. 2 Final Report on the Geology of Massachusetts, 1841, pp. 133, 540. 3 Geology of Rhode Island, 1840, p. 107. 190 GEOLOGY OF THE NARRAGANSETT BASIN. ENE.-WSW., and dip to the NNW. 53°,” is, in my opinion, approximately accurate. Both GC. T. Jackson and Edward Hitchcock agree in giving a northerly dip to the rocks at this point, from which it is evident that the Mansfield coal beds occur on the south flank of a syncline, and may be expected to reappear on the northern side of the axis or in the vicinity of the Junction. The probabilities are, however, that the sediments in this direction become coarser as the shore line is approached, and that the coal beds either thin or entirely disappear. The coal in Foxboro reported by Edward Hitchcock, nevertheless, may be a reappearance of the coal on the northern side of the axis. One and a half miles south-southeast from West Mansfield Station, in the Taunton quadrangle, red and gray sandy slates occur with nearly vertical dips striking N. 64° E., indicating, along with other outcrops described in connection with that atlas sheet, the much steeper southern side of the syncline and the passage to the adjoming anticline. The accom- panying section (fig. 27) represents the known and inferred portions of the structure through the Mansfield area: ‘, © .. , = . J = Ny . wea ’ P x ~ ca x x S Od oh x oe x ~ Bo x Y S ’ . ‘| S . . . . ‘ x ‘ 7 oore ’ - 4 Nt ’ ae . SN “P Ps S ’ oe 7 . , . : : K ’ / . , . 7 4 / 4 ~ o , *. : . . , . S 7 . ; v y ’ = a . low a = £249) E 7, Gs va Fic. 27.—Section of the Mansfield Coal Measures. The lines represent observed beds and their underground extension A, Foolish Hill granitite; B, Wamsutta series; C, Mansfield Junction. D, West Mansfield mines. E, vertical strata south-southeast of last. Analyses of two coals met with at depths of about 90 and 850 feet, respectively, in a boring put down near the old Hardon mine, have been COAL MEASURES OF THE DEDHAM QUADRANGLE. 191 published by Dr. A. B. Emmons.’ In the annexed table, analysis No. I is from the 90-foot coal, and No. II from the 850-foot bed. Analyses of coals from the Mansfield area. Fuel ratio( Vv I 16), | lessee | |, ELIE SaScq peasbe cosa tsores oeeeee | . 02 3.08 | Volatile combustible ....-..---.---- | 3. 76 6. 22 Warbonemecerne ys c cis ees a see TA, 24. 79. 68 Als Wesepeee O NOeETEe o se tere ae ts 20. 97 11. 02 | 99.99 | 100.00 Sul phureienies cease SaeiiSstie cls 56 | Thin sections from the core made in this boring, according to a manuscript report by Prof. Collier Cobb, showed that the amount of meta- morphism varies with the depth, being greater at the bottom than near the surface. Flora of the Mansfeld section. —'T"he following plants have been reported from the shales at Mansfield: Prof. Edward Hitchcock’ figured forms referable to the genera— Calamites. Sphenophyllum. Asterophyllites. Annularia. Pecopteris. Sigillaria. Cordaites (a form close to C. robbii.) Leo Lesquereux’ has described: Sphenopteris salisburyi (n. s.). Rhacophyllum adnascens. Pseudopecopteris irregularis. Teschemacher* described and named several forms, some of which are of doubtful identification: Neuropteris angustifolia. heterophylla. Pecopteris loschii. borealis. Pecopteris gigantea. Sphenophyllum truncatum (said to be un- known except to Teschemacher). Sphenophyllum dentatum—=erasum. Trans. Am. Inst. Min. Eng., Vol. XIII, 1885, p. 515. 2 Final Report on the Geology of Massachusets, 1841. 3 Providence Franklin Society Report on the Geology of Rhode Island, 1887. 4Boston Jour. Nat. Hist., Vol. V, 1846, pp. 370-385. 192 GEOLOGY OF THE NARRAGANSETT BASIN. BRIDGEWATER AREA. The available exposures from Brockton southward through the Bridge- waters indicate a broad syncline with low dips, and hence a much more shallow trough than that near Mansfield. Southerly dips are found in out crops from the granitites north of Brockton for a mile or more to the south of that city. At Cochesett, and thence southward, northerly dips are encountered as far as the northern part of the Taunton and Middleboro quadrangles, in the vicinity of Scotland, about 3 miles south of the limits of the Dedham quadrangle. Overlying the chocolate-colored sandstones at Brockton, described under the head of the Wamsutta group, occur arenaceous and argillaceous strata of slaty structure. Exposures of a bluish coarse sandstone have been made in opening new highways northwest of Campello, at the corner of Adams and Center streets. One and a half miles south-southeast from this locality, on the west side of Salisbury Plain River, bluish-green slates form a small outcrop. The cleavage is E.—W., and dips 45° N., the pre- vailing direction and steep dip along the northern border. Bowlders of erayish sandstone occur in the vicinity. Going southward across the strike, the next exposure is in the railway cut a mile east of Cochesett Station. ‘The strata here dip from 5° to 10° N., and afford the following section from the top downward: Section east of Cochesett Station. Feet 3. Conglomerate; pebbles of quartzite and smoky quartz ......:.....--.-...---- 10 2. Sandstone and arkose, gray....--..--.- 55 ys coRvet = ie Cea stays Run Naya tees are 10 shale blwesam dicompa tye se eee eet recat tps eee een ye tee ee ee 10 A thrust plane, with slickensides trending N.—S., was noted on one bed, and there are to be seen small vertical quartz veins containing cavities lined with botryoidal lmonite. About a mile south of the Cochesett exposure, coal is represented to have been found, in the area between the Hockamock and Town brooks. The place of this bed would be at a depth of about 1,800 feet beneath the Cochesett section. 1 Edward Hitchcock: Report, 1833, p. 277; Final Report, 1841, p. 129, also on geological map. C. H. Hitchcock: Geological map in Walling and Gray’s Atlas of Massachusetts, 1871. RHODE ISLAND COAL MEASURES. 193 The extension along their strikes of the several strata thus obscurely exposed can not be traced with certainty more than a few rods. As in the Mansfield area, there are no indications of the higher beds of the Carbonif- erous section, so well exposed in the deep synclines of Dighton and Taun- ton. The beds for the most part appear to belong to the few hundred feet of Coal Measures coming in above the red Wamsutta series. Unless the Carboniferous formation thinned out in this direction, the post-Carbonifer- ous erosion of beds of this age alone in this field must be measured as upward of 10,000 feet of strata. ABINGTON QUADRANGLE. In the southern part of this quadrangle more has not been possible than roughly to discriminate the lower reddish strata of the Wamsutta extension from the area occupied by the gray Carboniferous strata of the Coal Measures. The first-named series has already been described on page 143. There are about a dozen exposures of the gray series of the Coal Measures known in this quadrangle. Beginning on the northwest, in Abington, the gray series is seen in a small outcrop about 14 miles south from the granitite border. It is over 5 miles from this locality southward to the outcrops including Sachems Rock near the Satucket River, in the town of East Bridgewater. Sachems Rock is a knob about 175 feet long and 20 feet high, composed of massive-bedded, somewhat altered sandstone with bands of small pebbles of white and smoky quartz, a fine-grained granitic rock, and a slate of undetermined origin. The attitude of the beds is nearly horizontal, dipping, if at all, to the north. There is a pronounced cleavage striking N. 77° W. The western side of the ledge has been opened for the purpose of quarry- ing. The smaller exposures to the east along the street are like the first, showing to the eye abundant minute scales of muscovite. The cleavage planes maintain the same direction, and dip steeply to the north. These beds are on the southern side of the broad, shallow syncline which covers the southern part of the Dedham area, next north. They would come, in accordance with the supposed structure, low down in the Coal Measures. In Hanover, half a mile east of Drinkwater River, and about 2,100 MON XXXIII 13 194 GEOLOGY OF THE NARRAGANSETT BASIN. feet south of the northern border, is a probable outcrop of gray Carbonifer- ous sandstone in the street; it may be a large bowlder. Bowlders of the same lithological texture are abundant upon the surface. Southward to the limits of the quadrangle no outcrops have been found. Eastward, in the vicinity of Hanover Four Corners and near the east- ern igneous border, several outcrops of the carbonaceous series appear. Beginning on the northeast, in South Scituate on the east bank of Third Herring Brook there is either a large bowlder or an outcrop of sandstone with bands of small pebbles. Southward, where the road from Hanover Four Corners to North Pembroke crosses North River, there are good exposures, forming a narrow defile through which the river escapes from a broad valley on the west to the wide channel extending beyond this cut to the sea. The strata are sandstone and arkose with coarse grits, bands of slate, and carbonaceous matter, striking in an east-west direction and standing at high angles. On the south side of the river, in August, 1889, there was found in a coaly seam the stem of a calamite. One and a half miles farther up the North River, where it is crossed by the west road from the Corners to Pembroke, other exposures of the Carboniferous conglomerates and sandstones occur, on the south side of the stream. At the edge of the stream, in July, 1889, conglomerates and sandstones were exposed under a mill. The bedding was much obscured by joints. A few rods southward a blue compact sandstone is exposed, by the roadside, apparently overlying the above-named beds. Across the road and a few yards south of this cut a well was sunk, in July, 1889, through 10 feet of till into a dike of fine-grained, dark-colored diabase containing numerous inclusions of granitic quartz from one-eighth to one-half mech across, and a few pieces of feldspar. Angular fragments of red granitite also occur in the diabase. Half a mile farther up the river the stream lays bare a section of closely jomted sandstones apparently dipping northward. In the bank above the carriage road there is much carbonaceous waste. In the road ascending the hill at the head of the westernmost of the three headwater branches of Swamp Brook, in Pembroke, black clays occur, which are also met with in excavations on the adjoining land. The relations of these deposits are very uncertain. RHODE ISLAND COAL MEASURES. 195 TAUNTON QUADRANGLE. The eastern part of the area designated the Taunton quadrangle is nearly devoid of outcrops. In general it may be said that, except for a triangular area on the southeast equal to about one-ninth of the whole, this quadrangle is occupied by the rocks of the Carboniferous system. The strata which appear at the surface are mainly the harder conglomerates and sand- stones, thrown into anticlines and synclines. Of these structures there are at least two well-defined sets in the western part of the quadrangle: the Dighton syncline, with coarse conglomerates, coming to a nose-like end at Dighton in Richmond Hill; and the Great Meadow Hill or Taunton syh- cline, with the coarse conglomerates of the ‘Rocky Woods,” west of Taunton. Between these two great conglomerate areas lies the axis of an anticline which probably traverses the area eastward to Middleboro. On the northern side of the Rocky Woods tract is an anticlinal axis with nearly vertical strata, north of which lies the Mansfield syncline. The deposits so far recognized range from the highest beds in the for- mation, including the Dighton conglomerates, downward toward the middle of the Coal Measures section, including members of the Seekonk and Ten- mile River beds. The precise position of the lowest strata seen is not defi- nitely known. ‘The following notes pertain to important natural exposures of the strata and to artificial openings. Red beds— At one point in the northwestern part of the quadrangle, about 1$ miles southeast of West Mansfield Station, in the road on the west side of Hodges Brook, red slates are in contact with gray beds, striking N. 64° E., with nearly vertical dips. This is the only exposure of red beds known in this area, but whether they are an extension of the red slates in Attle- boro or are a reappearance of the Wamsutta group, there is no means of deciding. The red slates in the drift south of this point afford plainly marked flattened impressions of calamites. Outerops in Norton—Midway between Norton village and the southwestern arm of the Norton reservoir is a low outcrop exposing about 100 feet of conglomerates, sandstones, and slates. The strike here is nearly NE.-SW. The conglomerate is composed of quartz, quartzite, and granitic pebbles varying from half an inch to 3 or 4 inches in diameter. These beds can be traced eastward for a quarter of a mile. Unless they are overturned 196 GEOLOGY OF THE NARRAGANSETT BASIN. they overlie the following section, which is separated from them by several hundred feet of concealed beds. Near the southeastern end of the Norton reservoir are broad exposures of slaty arenaceous strata striking N. 54° KE. and dipping 75° 8. The fol- lowing paced measurements give the succession, from south to north: Section in Norton. Feet TAI yen ee eee NE oe ie wees ie oes COM ee SSS ST OOOH Cos tout 3 De Seng) sa osccsaanooudebe aoe unecdeecocosbobanccsococusdcosnbanoODOdbeCS 39 CMW yee: Benen eee Se SE ah ORAS Gon Sp DUH oo Ook O Soames ooS CuaAo aS 5 WISE GIRS so soba eau codon coabosucoue sudanso DD oo05 000 cote s soon GoDODOOS 2 RUSIGeces Sobeseooocuoos add Sb oowooonacsuDooOadqeeodce a eh Gagne te. CRN ERROR 12 (® Shimelsiomn®.si.55 s6ccdusonsua. cbavesouuadacudononoocooDoscUscuusecOmoOdaODON 8 fe SibhiGyohieg sb pose odds ceo ace cee Se obencetres noooueBbooDUU Ee odosDIOs CopOODO OOOO iL S} CEyNGIOMNG. .oocesecaso voobsuueoduooSedacsoeebo secs OopoeSUCocSs cadDO DCO PA eee eee Ces ee RRR Une as so Rdesa ano oobe Ase leap eSgoDUaGRoDOO boos 9 TO, Reyna) oa cacesoscsnandeuc Seaccuscquseus sooUs douose osm adasecedoscabdoas 18 TAS) neo ee Hee ee ne anlar is Cae aS nooo 6 oodosaondooseDoO AS 48 1D. Seynclronn-ccaccadoqcundoe socnde un qodaouoocs sHostu poeo dan dacesSoobddanoDS 22 WEXLER) a oo ee eo eee ebddnoouuooouesou saan so desopdonscaed noosa egos agdoout 2 IA: SeynGiGiOne osecsd4ossoodonoosobiogsesecdsodns concn compe oasHoSaDbO SoS DoOCeOS 34 The prevailing character of this section is similar to that of the beds in the same anticlinal fold to the westward in Attleboro. The absence of carbonaceous matter in the exposed sections is noteworthy. A few isolated outcrops in the village of Norton display beds of con- elomerate and grits, with variable dips. At one point the inclination is as low as 50° N. The general structure of the belt of rocks through Norton is probably anticlinal, for the Mansfield and Bridgewater synclinal trough lies on the north and the Great Meadow Hill syncline is well marked on the south. Winneconnet ledges— rom 2 to 3 miles northeast of the exposures in Norton oceurs the Winneconnet section, on the east bank of Mulberry Meadow Brook. There are here exposed upward of 200 feet of soft slaty rock of an arenaceous and often gritty texture. The cleavage dips west, and its strike is N. 49° E., but the dip of the bedding is not easily deter- mined. One and a half miles northwest of this locality is another exposure of similar slates. In both places the surface of the rock weathers into pear-shaped and rounded cavities, recalling the weathering of the ottrelitic RHODE ISLAND COAL MEASURES. 197 schists along the shores of Narragansett Bay. It is probable that the metamorphism of the beds along this anticlinal line has been greater than elsewhere in the eastern part of the basin, or ihat lower beds are here exposed. (See fig. 6, p. 120, locality B.) Eastward, outcrops appear in the vicinity of Scotland. About three- fourths of a mile south of the town pebbly sandstones strike nearly E-W. and dip about 20° N., forming a low monoclinal ridge with an escarpment facing the south. Beginning the description on the western border of the quadrangle again, the beds on the south side of this broad anticline are represented by a few exposures. The best of these is at a point near the western margin, on the west side of Chartley Brook, about 2 miles south of the Attleboro branch of the Old Colony Railroad. An old quarry here occurs in a knob of the gray Carboniferous. The strike is N. 69° E., the dip 15° S., and the following section is exposed from the top downward: Section in Chartley quarry. Feet. Gray sandstone with small bands of pebbles and flattened stems of plants, afford- TMOMEL ACES Ole COME ter arty seseo rarer assess tel ceabey SAE GAR suelo aay 2 earn ah PN cal ae 20 Black, compact, argillaceous beds, slightly micaceous, containing worm burrows of A Seoliiinone] InaloteR @xpOIetle e565 Sossbsdesseatctsececsouccs secon secdesce 12 Scolithus beds—'The worm burrows referable to Scolithus at this locality are somewhat sinuous or often recurved burrows filled with material similar to the micaceous rock of the walls. The tubes vary from an inch toa quarter of an inch in diameter. Where the wall has broken away from the internal cast the surface is either smooth or rarely marked by minute cross striations. The tubes are closely set, sometimes apparently in contact. The depth of the burrow exceeds in most cases 2 inches, and is probably much deeper, but, on account of the interlacing of the tubes, this point can not easily be ascertained. There seems no sufficient reason for giving a specific name to these forms, since they have no importance in indicating horizons even within the limits of this small basin. One and a half miles east by north of this locality are outcrops of compact argillite, succeeded on the south, near the head of Goose Brook, by gritty sandstones containing distinct pebble bands, the dip of the last being as steep as 80° S. These beds appear to be near the axial line of the 198 GEOLOGY OF THE NARRAGANSETT BASIN. anticline which is traceable westward along the valley of Tenmile River in the Providence quadrangle. Eastwardly there are no exposures along this strike line until we reach the small quarry of gray sandstones opened alongside the railroad between Britanniaville and the junction of the Attleboro branch railroad. About 1§ miles north-northeast outcrops occur on the west of Scudding Pond. About 44 miles farther east coal has been reported on the southern border of Gushee Pond, but the stratigraphy of this region is concealed by drift. South of this belt, in the latitude of Taunton, the Seekonk beds, over- lying the above, come in with southerly dips and disappear on the west beneath the synclinal axis on which stands Great Meadow Hill. The strata are medium conglomerates, sandstones, and shales. Coal has been found in the uppermost beds underlying the coarse Dighton conglomerates about 14 miles northeast of Great Meadow Hill. So far as has been determined, this is the highest occurrence of coal in the basin. Taunton waterworks section— Hastwardly and at a somewhat lower level, though probably in the horizon of the Seekonk beds, coal was again met with in sinking an artesian well for the waterworks of the city of Taunton. The well penetrated to a depth of 975 feet. The dip is reported to have been about 40° N. The following table gives the thickness of the several strata penetrated. The data were furnished by Mr. George F. Chace’. The measurements are approximate, and are based upon the nature of the materials brought up by the sand pump. The amounts indicate the depth of each bed. Record of artesian-well boring at Taunton. Feet. Superticialudeposits\(glacialkdniit) eee eee e eee eee ee neers 85 SAIN ASEOM G4 ee tL ie shete w elcia! care eee eicieneme chest ay sila ea eto eI ote re ey Ste PES RSE 95 @oaliypshales cyt 8 0h, SANE EAN. NR ret sieen ra) she olae ne ea earn or ent atone eer oye ey ese 20 Satelite ss iVoe GAN Se ae sce Rt tee ays ok ae ental eae Mee ee Ae eee Atle UO) Sandstomere esses kiss ose eda Gaye ates siegeler siere Ciel aba rs eta One Cite nets e=t= eee 20 Conglomerate quartZOsen yaar. cele late ee roi elae ese ee eeae erie Terre terae 12 SHS ON Roe See ee AL Sane hemes ou naa ogcidker oAGenod 30 Slate wl epee ik sie iaSisieeiees Ssh egalor ie Sa seers reise eave Sree ire iele re Sie esto ae Seren reer 81 SANGSFOME RA ras. srsietds 5 his ko Wiay eau rosecelcvler Sie haps eran ajetay EPA er eta rat a ISIN eye [crete pete ar 22 Slate tile sacier seizes. bee Gece be Lie eral eal eaten she Uliana 80 1Fourteenth Annual Report of the Water Commissioners of the City of Taunton [for 1889]. Taunton, 1890. Plate opposite p. 28. RHODE ISLAND COAL MEASURES. 199 Record of artesian-well boring at Taunton—Continued. Feet. Sand stoneramclycoal iyi S lute yee teje a avsyesete een e teens eee eves Manne eee Apa ore eu aus 15 Won PlOMErAabe nq MAartZOSO ss sese) sis Sies lee vcpe vere cove lesebare vars ie tet tereae eater Sher oo yons teven ciety ce aes 13 WoaliyShalesieerresess cis a)s a1 oi secs tie Sal yee eT ered See Fae ra seas eet oes 97, SlatencoalyomadksamG Son eyacrcicrenccaperis ten tecye epew ste Rooney cree ewe ore ters iaec le eae Pa page 15 SEEVEVGIS COV TTS SES es lace a eh are Aas Nee ed ioe are ae me SRA ERS eS 5 Goallysslarte; eer crates Se -letsstve baaS Pawtucket. 265, Odonopteriskobtusilobat, esses eee eee cee ee eeee | ? 2Tbid., p. 229. OCCURRENCES OF COAL. 205 A more complete list of plants found in the Rhode Island Coal Meas- ures has been compiled by the Franklin Society of Providence, and published in its Report on the Geology of Rhode Island, 1887. COAL BEDS. The following account of the coal beds in the basin, written by Edward Hitchcock, who descended into all the accessible mines, sets forth the condition of things as late as 1853, since which time few mines have been opened: 1. Beds of coal in Mansfield.—These have been opened in two parts of the town. One is near the center, where a shaft was sunk by the Mansfield Coal Company, some fifteen years ago, 64 feet, but only a little coal was found. About the same time the Mansfield Mining Company sunk a shaft 84 feet near the Hardon farm, 2 miles southwest of the center. A drift was then carried across the strata, and it is said that seven beds, of various thickness up to 10 feet, were found. Dip of these beds, 53° NW. Strike, SW. and NE. More recently, in 1848, I believe, the Mansfield Coal and Mining Company, through the enterprise and perseverance of B. F. Sawyer, esq., sunk a shaft near the same place, 170 feet and 10 feet in diameter, from which, according to the statements of Thomas 8. Ridgway, esq., the engineer, they have carried a south tunnel 660 feet, and other tunnels and gangways to about the same amount. Not less than thirteen beds of coal have been crossed, but none of them thick. They are very irregular, sometimes swelling out to 6 or 8 feet in thickness, and then pinched up to a few inches. The dip varies from 30° to 70° NW., and the strike is nearly NE.and SW. Although these excavations are not far from the old Hardon mine, the beds are said to have little correspondence. 2. Bed in Foxborough.—This is only about 2 miles from the Mansfield beds, and two excavations were made there several years ago, aud good coal obtained, but the pits were filled up so that I could not ascertain the strike, dip, and width of the bed. 3. Beds in Wrentham.—In the south part of the town a pit was sunk many years ago, about 170 feet, mostly in dark carbonaceous slate, and several beds found. The coal which I have seen from this spot is not good, having 40 per cent of ash. Strike of the bed, nearly E. and W.; dip, 45° N. 4, In Raynham.—An outcrop of coal appears in this town, about 3 feet thick, which has not been explored, except a few feet. Strike, N. 50° E.; dip, 45° SH. 5. In Bridgewater.—Indications of coal were shown me from the rock thrown up in digging a well in the south part of tne town, but nothing further could be learned. 6. In Taunton.—Two miles northwest of the town, a similar opening was shown me, but I could not learn the dip and direction of the slate. Four miles to the west of the town, I was told, similar indications exist. The same is true of West Bridge- water, and in Berkeley coal plants are found, such as usually accompany beds of coal. 206 GEOLOGY OF THE NARRAGANSETT BASIN. 7 In Cumberland, Rhode Tsland.—Thisis called the Roger Williams mine, which was opened many years ago; but the works were burnt, and the explorations aban- doned, but they have been resumed within a few years under the superintendence of Capt. Thomas Martin. A shaft has been sunk 300 feet perpendicularly, into which I descended with Captain Martin. The old bed, whose strike was nearly NE. and SW., has been abandoned, and by carrying a horizontal shaft 260 feet a new bed was struck, which, at the place, runs nearly N. and 8. and dips west about 45°, The average width was stated to be 15 feet, and in some places 23 feet. If this be not a mere protuberant mass, occasioned by lateral pressure, it indicates a larger amount of coal than I have’seen in any other mines in this coal field. 8. The Valley Falls mine—This is scarcely more than a mile south from the Roger Williams mine, yet the strike of the beds will not allow us to suppose them connected. The operations here are carried on by the Blackstone Coal Company.