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REMATIKABLE LANDSLIP IN PORTNEUF COUNTY, QUEBEC 
 
 BY 
 
 GEORGE M. DAWSON 
 
 [From Bull. Geol. Soc. Am., Vol. 10, 1808] 
 
b^LOSOVV, O' "^ 
 
 Ace. No. 
 Class Mk, 
 
 Pup. 
 
 Date Rec'd 
 Agent 
 Invoice Date 
 
 Fund 
 
 Notify 
 Send to 
 
 Presented 
 
 APR 2 - 19?9 
 
 \{. xia^'^^'^^ 
 
 Exchange 
 
 BINDING 
 Material 
 
 Binder 
 Invoice Date 
 
 Cost 
 McGILL U IVERSITY LIBRARY 
 
 ROUTINE SLIP 
 
 \ 
 
liY (ii-.(>i!<:i': M. n.wvsos 
 
 Cdtlllllt!^ 
 
 Kxiiminiitiim iiwulo 
 
 (•h:u-!if.tcr of tlioi'.imitry ■■ 
 
 Mo.lo au.l extont of tlu- u,ovnu...t 
 
 AMumut of maUTiivl involv.Ml 
 
 r.xi.liiimtion of ilu> .■i.t.i«lro|.li.' 
 
 I'lMtiMHion fruiii siiiiiliir dixisUTs 
 
 Si,uil,ivo.Mmn:n.M.sintl,..>anH.n.g,on 
 
 I,,,„,.rV AND CoSS.arKN.KS OK TUK LANUSUr 
 
 <>.. >^av :, .SOS. . i=^;'-i->;--;;- - .:;;::;:;r :;;;;::'S"' 
 
 Saint. AiuumU. lalVnva.", pansl. ..f^uuil lln.unt, 
 (484) 
 
 1X4 
 
 IS.-! 
 
 is.-. 
 
 in.-. 
 
 tHT 
 
 487 
 
 4S'.I 
 
 4S9 
 
 of lllO 
 
 . The 
 
l.'<4 
 
 , IS.-, 
 . IS.-. 
 . is.-, 
 .. -tsT 
 . 487 
 . 4S<I 
 .. I.s'.l 
 
 tllO 
 
 The 
 
BULL. GEOL. SOC. AM. 
 
 VOL. 10, 1898, PL. 51 
 
 JSi^^B^"^. 
 
 
 Kiiii 
 
 IK l,--fm <1.IUS M KVMIIIS I'.M' "I l.\M'-lll' A li 1: V 
 
 l-'ii.i 111: J.- I'.IXM hi: \M.i i\ "ii'n>iii- l.wi'-iii', wiiii 1. x \ h^l ii- i M 1 1 i i is lii>iv\o 
 
 RIVIERE BLANCHE LANDSLIP 
 
HP 
 
 t.AND.SI.n- IN I'<)KT\Ki:i.' COINTY, (iUICnKf! 
 
 485 
 
 I 
 
 Hlip took pliico oil tl„. ,.iVHt Hidi' of the river, at ii di.stivnce of n inilcH from the vil- 
 liiKf of Saint CiiHimir. Tin- rcHiiits were (lisustroiis to tlio fiirnicrH wliosc property 
 wiiH iitrectod, one life wan lost, two inliaiiitfil Iioiih.'h. a .hi-IiooI-Iioiim-, two \num, 
 uikI H.'vcral oiithuiMiii-,'^ were dt'^'troyed or engulfed, and cattle, liorHeH, and other 
 live Htoek perinlied. 
 
 KxAMINAIloN MADK 
 
 Oil .May I'i) I visited and t'xaiiiiiie«l tlie locality, takini? Home i)liot()j;rapliH of the 
 Hceiie, and a few days later, at my recpicst, Mr K. Chalnier.s, of the (ieoloKical Sur- 
 vey, acconipaiiieil hy Mr ,1. Keele, inaile a doner Htudy of the circnniHtanceH hh 
 well as an approximate survey of the (ilacis and procur»"tl additional phot()j;raplm. 
 The following brief tleHcription is Imsed partly on my own ohservations, in part 
 on those of Mr Chahiiers, and is intended merely to outline the chief facts of in- 
 terest, from a jrcoloj,'ical st!tnd|)()int. respectinj; a mode of denudation that appears 
 to have been not uncommon in the day-floored plain of some parts of the Saint 
 Lawrence valley. 
 
 ClIAUACnCK OE- rilK Coi'NTIlV 
 
 .\t the place in question, the i.'ivicre liiaiiche, a small stream, occui)ies a valley 
 
 rnnnini; fn lorth to south, about I, ODD feet wide, i)etween slopiii",' banks, IV) to 
 
 .'!.') feet liijth, and nearly uniform in this re.speet. The surface of the country in 
 the vicinity is for the most part under tillaije, and is practically level to the eye, 
 l)eiii>r a terrace-llat or plain composed of the marine Pleistocene deposit known as 
 Leda clay, the whole thickness of which is not here anywhere shown. The day 
 is occasionally covered by arenaceous deposits a few feet thick and referable to the 
 Saxicava sands. 
 
 To the north of and adjoininn the wide crater-like depression producei by tlie 
 landslip here particularly described there is, h)wever, an irrej,'ular depressed 
 area of nearly the same size, now under tilla<,'e, that evidently represents the site 
 of a nincli earlier slip of the same character. Still farther to the north, and at a 
 distance of .■)0 chains from the recent slij), the road, which runs parallel to the river 
 valley and near it, crosses a low rid<?o of boulder day. This material may be pre- 
 sumed to underlie the Leda day elsewhere, but the subjacent ro(;k is nowhere seen 
 in the vicinity. 
 
 MoDK AND lv\ri:Nr or run Movk.mknt 
 
 A small runnel of water appears to have entered the IJlancihe valley at the point 
 where the material of the landslip subsei|uently found issue, and 1 was informed 
 that previous to tlu^ main slip a small slide had been noted to occur at this spot. 
 •At half i)ast five in the in.-rninj,' the inhal)ilantH were alarmed by the movement 
 of the soil, which then suddenly began and continued for three or four hours. The 
 imnuMliate bank of the river valley appears in the first place to have jjiven way 
 aloiij;; a front of about 'JOO feet in width, and the j;ap thu lade rapi<lly extended 
 inland, forminj; an openins; throu!j;li whicli a ^rreat body of clay behind rushed 
 tumultuously out into the l?liinche valley. .\t a short distance from the liank of 
 the valley the width of the area atl'ected j;reatly enlartreil, the sides of the depres- 
 sion collajisinj; and falling; into the jjulf, until a crater-like hollow of bottle-sliaped 
 outline and openinji; on the valley by a narrow neck was produced. 
 
1st; 
 
 I'lK" KKIilNfiS (»1' TMK N K\V YOJiK MKKTlNii 
 
 The iiiliiil)itiiiit.« oii the Hpol wcivho iinii-li alarmed that they naturally <liil rmt 
 (iliHiTV;^ tilt' actual proKrcHHof tlic lamlMlip with ^rt'at preciwion.buteyf-witnPHscHde- 
 HcrilM' till' puHfiiKc nf lildck.M and |iyraiiiids of day tlinxiKli tlii! oridce to tlii' river 
 valley ax lioiiiir very Mwil't and rcscniMinK' Mtcanu'rH in motion on a river. Tlicoe- 
 cnrrence, in fact, may lie naiil to have resomlilcd the hurHtinj; out into the valley 
 of a lake of liipiid nnid, hearinu with it oiitHtandin^t an<l unhroken lilockn of clay 
 di'tacli(>d from the .ijdesof the c()lla|wini; art'a. 
 
 Kiia in: \.SIyi trli-jilnn slinimi./ A,. a ,,i iMndslip (hmiznntal liiu,i;i), I'ml nf I'hiii-tilh.l Hii;-r;-<illiii 
 (rirtifiil Itiiiiiij). and .i/./i.uriwio'f Ihiumlitrii nf an otn-ient Liiii'lfliii af tin saaif h'iml 
 
 On entering the HIanche valley the flood of clay spread upstream for some 500 
 or 600 feet, ponding hack the river water, lint the greater part, descending the 
 valley for nearly two miles, tilled it for that distance tii a maxinuim depth of fully 
 2o feet, causing the destruction of the rich meadows along the valley, besides that 
 of the agricultural lands immediately ali'ected liy the collapse. 
 
 When examined by me, the actual landslip was represented by a depressed area 
 bordered by clay clitrsfroni 1.'^ tooO feet high, 1,700 feet in maxinmm width, with a 
 
r.ANrtSI.II- IN |'<.|!TM.:( !• (..INTV, (^1 KIJKC 
 KivutCHt l...mtl, of ;!.()()() f,M.( nn,l :,„ aivii .,f S.i a.T..> 
 
 487 
 
 X. Tilt" 11, I- of tlii.Mih.pn-HHii.n 
 
 w„ .nn...l ,,y nvu, u.. ,, ,. „,,, , ., ,,.,..,, ..^Hay. .{uZ;:. ^Z^ 
 
 ... ..CM, «M,l otlu.r . ..I.ns a,..l sn.all ..f water l.e.va...l tl.... ■ ; alll. , «1. i, i„ 
 
 tI;:; ' : H-;^ ""'" ""•";. ^^^ ^'■'■" •""'•"^ ""•-"'"• ■•— .;>..• „;,„;;„: 
 
 u, kH .,( t ...... ..,„,.,.,,- In.,., a wo„.l.loi, ,.art of whi..). ..ill ,,.„.ains near the 
 
 1 .-u.l n •-.••....•. sl,ow...l vc.iy .•l..H,.ly th,. .lhv,-ti..„ .,f ,|.,w of tl.., ,.,aHH. Tl... 
 ••Iwmnel „l ... I'.lam-l.o h.-low tl... o.ill.... of ,1... sli,. wa.- ..n.i,.dv .ill..,!, an.l . 
 
 y out into the Hlanche 
 
 Amount <.k Maikki ai. involvbi) 
 
 Tlie quantity of iiia.oiial whicii .hiiM poured sikI.IcmIv 
 vail. ■ 
 cnr. 
 
 Tl 
 at wl.i..h tl... ma.l (\,nn..,ly pans.-.l, „..a,- ,|... ,.„,nu,..e to the ..anow ontle.,'wa7 
 Hcconlmy to har<.i,....,i,. ol.He.va.ioi.s hy M.' ChalM,,.,.., about 10 fo..t only. Tl.J 
 «I.prov„..ato .1,11..,,.,..... hetween the av..,.aK.. level of the botto... f,.,,.. the l...a.i to 
 
 he ,..-e.sen wuer level .n .1... Hhm..h,. vall..y, a. .,11.,.. .o .1... sa,„.. au.ho.i.v. is 
 
 bet.veen 2 an.l 2yeet, wh,le .he slop., of that pa... of ,la. H^^ 
 
 oi.lice of f I... slip .,, .1,,. oxt.en.i.y .,f tl..- (l.,o,l of day is n..t ....i..!, ' 
 
 I > .s approx,n.at..|y ..H.,n.a...,l at ..:!..m.,.„k, ..„„ie .V...t, with a total wei^rht, m- 
 ; IMK to .1... spe....... ,May.ty .l.....,.,„i,,.d, .,f alaau ^572. U;! t..,,s .,f 2 
 
 ll.eslopeof.l.eo,-,K,nalHurfa..elV the l...a.l of thec^ollupse,! a....a to the point 
 
 feet. 
 
 more than 30 
 
 K.\,.|,ANATION OF TIIIC CA.|-Asri{OI'IIK 
 
 The l,>r|.t slopes in.li..ale.l by tl... ahov.. Iitr,i,-..s show f;,at H.. :>-,.,» of ehv n.u«t 
 
 .ave.m.nl«.e.laH.,„i,l bo.ly when h. n.o.io... M..Chal,;..rH sut^Kesis that a l.,wer 
 
 IK.,1 .)r th(. ,.|ay, ,n ..ons,.M„en..e of .ho iinpenn..abiiitv of .he s,il,ia..ent honl.ler 
 
 elay,beea,neex....ptioMallysatui.a.e.l, fo,.minKasli,li„i, piano np,j,.whi..l.. he n.oie 
 .•oh...vnt overlyin- n.ass,.s n.ove.l .low... This wo,.i,l l„. i„ ..o.irn.-.Mii v with ll... 
 e,v|,lanat.on ns.ially (and ,„.obably in n.os. .'ases ..o.TW.tlv) -iv..,. fo.- lan.'islips ....l 
 ,. se..n.s v..,y hkely .ha. son.e.hinj; ..f .he kind niav have been ..on..e.-n..d i-.' .he 
 initiati..n .d the slip here described where it hewan on the bank of .he l!lan..he 
 valley. J. appea.'s .o n.e, however, .l,a. .he ^rea. and sudd.... disdiai-jre .,f Hav in 
 this ease should .-ather be attrilMi...d to th.. .•ha,.a.t..r ..f .he Nva.....-sa.n.-a.,.,l .nasn 
 ■M a \vh.>le, particularly as no eviden.v was found of anv H|.e..iaiiv permeable or 
 finentbe<lan.l no .nid..rlyinK si.rfa.... either of boujd,..- ,.|av or ro..k i.s anvwi.ei.. 
 exp...-ed. I. will be n.ted that this landslip dillers verv nia.k...llv in el.'a.a..ter 
 fr..n. the ordinary form, i.i wl.i.ii .he subsi,l,.iK.,. ufvms alonj,' an ..xtended front. 
 
 Thi-ee representative spe<.i,..ensof.hee]ay,..<,lle,.ted by Mr ( 'hah. ....-swhilestill in 
 a nearly satni'ali.d..onditioii w..|vsMbiiiitt.d to a .■a.vfiil ..xaiiiii.ation in the labora- 
 .oi'v ..f the .^urv..y un.ler l»..,.l.,r lloirn.a.nrs .-iipervision. A i.i,.an of the resultH 
 ..b.aii....! shows. he speeili,. jr.a-.ityof .be elay as ie(...iv..d to have been l.<)12 
 e.iuivalent to a wei^rbt of 1 l!i..-) poimds ... .h....|ibi.. foot. Tl... day as reei.ived was 
 f'.und capable ..f absorbin;; a small a.ldi.ional ainonnt of water, varvinu fr<.ii. 7.0 
 t.. 0.2 per c.iit by wei;:!... Apart fi'o.., the water, i. ..oiisistt.d of ;;,•)!.-. per cent of 
 arKillaceouH inatt..r an.l 4;i.:i per ce,i. of silt. When (iilly satiuat...l it ....n.aint.d 
 on .he avd'ajre, which varied li..lc in the th.ve san.ples, 2;!,5 percent of waterby 
 wei<,'ht or nearly 50 percent by vol.nne. 
 
■188 
 
 l>K()('Ki;i)IN<iS OK TllK M:\V V015K MKKTING 
 
 It will lieiioti'il that tlio I-oila chiy hem coiitiiiiis a conHidonvhk' proportion of 
 HJlt as compaieil with tlie aru'lllacfoiis inattiT proper, hwirinj,' out an ohsfrvatioii 
 made to thof*anie eli'ect on innpeftioii of the locality. The lariro amount of silty 
 matter preHont would render the day nnusualiy pernieahle, and it seems, there- 
 .ore, to he prubalde that the water saturated the mass by descendlnj; directly 
 through it from the surface, in a manner which would not have been ])()ssilile in 
 the case of the more purely arj,'illaceous clays of the same au'e usually found. 
 
 In Rankine's Civil Engineering it is stated that "the [ire.sence of moisture in 
 earth to an extent just suliicient to expel air from its crevices seems to increase 
 its coetlicient of friction slitrhtly ; but any additional moisture acts like an unguent 
 in diminishing friction and tends to reduce the earth to a semiHuid condition, or 
 to the state of uuid."' It appears probable that in this i)articular instance the 
 silty clay, surcharged with water, stood in a condition of unstable e(iuilibrium, re- 
 taining its soH<lity merely by virtue of its unbroken molecular texture, and that 
 at the moment in which it became subject to internal movement this texture gave 
 way and it hqised into a nearly liquivl mass, the particles rearranging themselves 
 with some freedom in the water previously locked up in its pores. 
 
 The fact that many clays when once completely dried and then innuersed in 
 water lose their plastic character and crumble down into an incoherent nmd, shows 
 that the natural texture is an important element in their coherence and plasticity, 
 and one which does not appear to have been fully recognized in connection with 
 experiments on clays and soils. 
 
 The high siH'cilic gravity of the lluent portion of the mass in this case, no doubt 
 enabled it to carry the unbroken blocks of clay along that were snpi)lied by the 
 collapsing sides of the crater-like depression which was immediately formed, and 
 when not subjected to stress these blocks coiitimied to retain their original lirm- 
 
 ness and form. 
 
 The fact that the great mass of moving material was disciiarged througii a com- 
 paratively narrow orilice, shows that the bank of the valley through which it 
 passed was nuich lirmer in character tlian the clay forming the subsoil of tin* 
 plain beiiiiul. This no doubt arose from the natural drainage of the clay along the 
 bank preventing its complete saturation. The same -xplanatioii no doubt accounts 
 for the northern limit of (he collapsed area occurring along the liiK* where the sur- 
 face begins to slope down toward the hollow of the old landslip already men- 
 tioned, but the limiting causes on the east ami .-ionth are not clearly ajiparent. 
 
 IiKluiries made on the spot showed that no excessive rains had occurred imm.- 
 diately pn'ceding the slip, but that a great depth of snow lay upon the ground 
 dm-ing the latter part of the preceding winter. These statements are conlirmed 
 by the meteiudlogical observations made at (Jnebec, about U) miles distant, which 
 have been obligingly I'urnished by Mv K, V. Stupart, director of the siieteorological 
 service. From tlie-^e it ajipears that the total preci[iitation (in rain or melted 
 snow) for the mouths of Novcmlicrand DecemlK'r, IS'.t?, and in .January, >hin>h, 
 and .\i)ril, 1S'.)8, was slightly below the normal for the [last 1' I years, but that in 
 February, 1S98. it was two inches ab<ive the average, in the form of an al)normid 
 exce.ss of snowfall in thai month of I 7. 1» inches, the total snowfall for rebrmiry, 
 being 44.2 inches. The ground was thus heavily burdened with snow in the later 
 winter. During .\pril moat of this melteil and the ■loil itself thawed, permitting 
 
BULL. GEOL. SOC. AM. 
 
 VOL. 10, 1898, PL. 52 
 
 '■'"■I "> I. - N"iiiii i;i,..r Ml l,\vi,.| I,, \|,Ki. Mi:« 
 
 1.11 !■', \M « \i:ii Fi:o>i 
 
 \K,Mi I Ml. I Hi i.kt 
 
 I' i''i i:i -■ ' '1 I.s\i.-i ir, lis.. i.i« Mill r.i vs. 111. \ VI 1 t;\ 
 
 RIVIERf BLANCHE LANDSLIP 
 

LANDSLIP IN I'OUTNKUF COUNTY, QUKBEC 
 
 489 
 
 ti. 
 
 V 
 
 the absorption of tlic watin- and ivHiiltin<r, early in Mmv, when tlic day IhmIs \m\ 
 thus l)(>conic thoroufjlily .saturated, in llie landslip which has heen described. 
 
 I'kotkction iKOM himii.au Disamtkrs 
 
 The only way in whicrli the reenrrence of sueli slips in regions of country of the 
 same character and under similar exceptional conditions of precipitation can be 
 (.'iiarded against ai)pcars to he the i>rovisioM of effective surface drainage, such as 
 to carry off the excess of water before 11k> ratlier slow iirocess of absorjjtion by the 
 siubjacent clays can take place. 
 
 ISl.MII,AU OrCl'Klil'.NCKS IN THIO S\MK KkgIOX 
 
 In a i)aper entitled " L'Ebouiis do Saint Alhan," '• Monseigneur [.atlanune has 
 given an e.xcellent account of a landslip tliat occurred on A])ril 27, bS94, on the 
 Sainte Anne river, (hstant about 7 miles only from that above described ami af- 
 fecting similar deposits of the saint, plain, altiiough at Saint Alban a laru'e part of 
 the sli<le consisted of the Saxicava san<ls, there developed in great thickness above 
 the Leda clav. 
 
 The landslip at Saint Alban was also umch larger than that on the Blanche, an 
 area more than ;{ miles in length along the river and about 7,700 feet in greatest 
 width having moved bodily down into the valley. Fivi> or six larm-houses were 
 destroyed or swallowed up, four lives were lost, and the entire mass of the slide is 
 estimated at from ()00,0l)0,()()0 to 700, 000, 000 cubic feet. 
 
 The landslip at Saint Alhan was also different in its cause and character. The 
 river was first dammed by a comparatively small slide, and when tlie water thus 
 held l>ack eventually broke through, its undermining action on the high banks 
 of the valley was such as to precipitate the collapse of the nnich greater area above 
 noted, t 
 
 A brief description of a landslip almost identical in ciiaracter with that of the 
 Blanche and allectiug a similarly situated part of the same Saint Lawrence plain 
 has, however, i)reviously been given by Sir William Logan in a pai)er read before 
 the (ieological Society of London in IS42. :]: 
 
 This landslip occurred on the Maskinongc river, about oO miles to the southwest 
 of the Ulviere Blanche, on April 4, 1S40, and waa examined by Logan in the follow- 
 ing autumn. Like that on the Hlauche, its outlet through the l)ank of the valley 
 was narrow, ami its greatest width, about (iOO yards, occurred at some distiince 
 hack from this bank. The length of the collapsed area was l,;!00 yards, and its 
 area about .S4 acres. tht> depth of the depression being about ;!0 feet. The nearly 
 licpiid clay flowed both up and down the valley of the Maskinonge for a distance 
 of about three-cpiartersof a mile in each direction, hearing with it large blocks and 
 masses of unbroken clay. The whole movement was effected in about 15 hours, 
 tlie first nui.ss of clay detacheil being al)out 2t)0 yards in width by 700 in length. 
 
 ♦Tniiisiii'tions Royal Soniiity of Ciiniiilii, vol. xii, piirt iv, 18'Jt, p. ti:i. 
 
 fsiiir-c till' present piipcr wii.s rcml u .short iiutis liy tlic siinie tuKlioi' on tlie HIiuielie liinilslip liiis 
 lii'eii piililislieil in the IJeiicii't of the Coinniissloner of Coloniziilion iind Mines of (/iieliei. fm- l.siis, 
 p. l:U. 
 
 { I'roreeili.ii^s of llie (ieoliv^tiiMl •ioi'jety of l.oii'loii, vol. iii, p. 7Ci7 ; iilso liife of Sir \Villi;im 
 I.OKiin, p. !!."). 
 
„„.„;.,. l,y 0„. .li„ «a» J,.»....K.,1 ,y I-'': - ' ;» f „,: , :," , ,;,„., ,,,,.,,,-,.,1 
 
 "■• "'":;:;;:;:t;,;t;. \ ::;;;:::. '^'.'.'""--^ 
 
 of.ior inat.'nal b>>lovs tlu lay, nm however, mv ii,t(Mpi-etati..ii of 
 
 .,,,y have .Krurml on a slopni^- he. ..f .ock. ' ' ^J^J; '^ ^ • „^. .xintenee 
 U.;nu.t. on the Blanche he eo,-reet . --^ ^ :;;^ ,^:, : ^^ the satuvated 
 
 ';Zn^Z^:^X^ '-in. heen h.oUen th.oa.h in the first n.t.nce. 
 
ternice-Ha'. 
 eft hctwceii 
 
 LCt ollStTVCll 
 
 ic expliiiii'''! 
 yin^ nick or 
 ' nioMMiiont 
 ■pretation of • 
 he existence 
 hesatuniU'd 
 to till" lower 
 ;tance.