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Lorsque le document est trop grand pour dtre reproduit en un seul clich6, 11 est film6 d partir de Tangle supdrieur gauche, de gauche d droite, et de haut en bas, en prenant le nombre d'images ndcessaire. Les diagrammes suivants illustrent la methods. 'rata o >elure, I a 3 32X 1 2 3 1 2 3 4 5 6 I TAM • [From The American Journal oi Science, Voi.. Ill, March, 1897.] THE SCOURED BOWLDERS OF Tiit5 MATTAWA VALLEY. By F. B. TAY1.6R. I bbhh ,'i rt-:' It-*" ^ I 2(»S Taylor— Scoured Bowhhrs of the MoHowa Viilleif. Akt. XIX.- T/ie Scour.'f Boii4v>i of the Mattamt VaUcu : by F. P.. Tavl(')k. Introduction. Ihe autlior spent the last week in Sepfeml.e.- and tlio tirsr iialf of October just ])asscd in explorin-j: the vaUey of the Mattawa river in the Province of Ontario. The chief object of search was to discover whether tliere is any clear evidence of the recent flow of a great river eastward alon«,^ this course to the Ottawa valley. For this is tlie site of a su|)posed former outlet of the upper Great Lakes. It has been supposed, first by Mr. G. K. Gilbert, and later by Prof. G. F. Wright and the author, that there was a period since the disajipearance of the ice-sheet during which Lakes Superior, Michigan, and Huron discharged their waters eastward to the Ottawa valley along the present course of the Mattawa river. During this period Lake Erie alone retained its outlet through JS^iagara river to the basin of Lake Ontario. It does imt fall' within the intended scope of this paper to discuss all the facts relating to the existence of the Nipissing-Mattawa river, as the ancient outlet river may be called, nor'to discuss exhaustively the facts relating to its duration and date. It will sufKce here to state that from several kinds of evidence the existence of the great outlet river is believed to be established beyond a doubt; and further, that it endured for a comparatively long period of time and ceased to exist probably considerably less than ten thousand_ years ago. Hence, wlii'le it is geologicallv a very recent thing, it may very properly be spoken of 'in a historical sense as ancient. _ No more conclusive evidence of the existence of the ancient river could be expected than that which has been gathered this season from a study of the numerous bowlders that lay in its rapids. The volume of the river, it is fair to assume, was practically the same as that of the St. Clair river to-day, and was equally steady in its flow. In rapids of moderate velocity, where the river flowed over a sill closely paved with large bowlders, the action of the current rolling 'small quantities of gravel over, around and between the bowlders produced cer- tain \yearing or scouring effects which are very characteristic. The forms so produced are not known to be made in any other way. It is the object of this paper to present a brief account of these peculiar bowlders as they appear to day in the valley of the Mattawa, many of them as much as forty feet above the present river. A few remarks will also be added about the, conditions and the processes of their i)roduction. Taylov — Scoured Hoxolders of the Mattav^a Valley. 209 The bowlders which sliow tliese tnodlHcations are almost all lar<^c, rungiii<^ from alujut two to twciity-tive or thirty feet in diameter. Bowlders of large size are extremely miuierous on the areas where these forms are found, completely covering over the surface of the iirouud. They are all of very hard crystalline rock; some are red or giay granite, aiul some are greenstones, hut by far the greater nuniher are of the hard foliated gneiss which is s(» common in the surrounding region. j\[any of the large bowlders of gneiss, even after the long exposure to weather which they have undergone, show no signs of fracture or breaking. So far as ol)served the bowl- dery areas of the former raj)ids of the river appear to be asso- ciated with belts of niorainic accumulation. Varieties. One may best learn the processes by which scoured bowlders are made by stu 'ying the action of the current in l)owlderv rapids of the modern river at a time of low water. In passing over and among the bowlders the current is very much dis- turbed. It is tui'ued aside suddenly and thrown this way and that; it strikes against the front or the sides of some bowlders and passes through narrow passages between others ; it glides smoothly over the tops of some and falls heavily on the tops of others, and in a few cases it is thrown into a voi'tex whirl in an angle or slight depression on the surface of a Ixtwldcr. Just as the billows in a rocky ra|)id remain constant in \)os\- tion, so these various turns and whirls in the current beneath the surface remain constant in place and action so long as the bowlders lie unmoved. Tims the currents that play ujiou a bowlder are generally constant in the particular manner of their action. Where sand and small pebbles are being borne along in small or modei-ate (juantities. they follow the devia- tions of the current from bowlder to bowlder, and each sand- grain and i)ebble does a little work of abrasion as it goes along. Every t)ne that follows the same course among the bowlders perforins its iota of work U])on the same j)art, so that the wear on each bowkler comes where the current imj)inges upon it. In the course of time, but vei'y slowly, the bowldei's are worn into the fantastic sha[)es which are here called scoured Ixtwlders. The forms which the liowlders take under the scour of the sand- and pebble-bearing cui-rent are quite varied. But after examining several hundreds of specimens it became ai)|)arent that all could be classitied according to their forms under a few heads, although a few individual cases would have to stand as intermediate forms. Six varieties may be distinguished as follows : I 3. 1. 5. 210 Taylor— Scoured JiowlderH of the 2/attawa Valley. Scoiiretl bowUlors. 1. Picrct'd (Uiiig-bowl(lers). 2. liawined. Niclit'd. (JutlLTt'd. Facetted. 0. Smoothed. The table of varieties of form as ««;iven above is offered only j)rovisiotially. For it is (juite probable that a more extended study of the subject would suoom creek did in fact supply a lar(» to »*>(» feet above the modern A[attawa river where the creek ei'ters the old channel. The intiueiice of the ancient outlet current is shown by the fact that these sediments have been carried down that side of the channel (juite exlensively and spread over part of the bowldery terrac^e. At Des Epines rapids the o;ravel supply came from the xVmable du Fond river, whicl. enters on the south side less than half a mile above. This stream is nearly as large as the ^[attawa itself and it cuts extensive gravel beds a short distance above its mouth. On the other hand, in the bowldery rapids at the head of Lost river (foot of Turtle lake) no basined bowlders and few even of the less pronounced forms of scour were found. They '21'^ 7't/>//nrSt:<>i/r>y/ Hoinlders of the JIattaiva YdUeij. appcaivd to he ahsent also in tlie ancient bowMery nipids next helow Pini'si hay and at the IIa|)ide des Koehers Ixdow Lac d(!s Aii«nilles. At all these places the cnrrent issued directly from a lake anl)!i!s ami sand to spin round and round on one particular sp(»t on the surface of a, bowlder, the |)rocess of wearing; out a basin is beo'un. (Jiven only time enouii'li, with constancy of tlie con- ditions on which the whirl depends, and the basin will sink deeper and (le(>per into the solid bowlder until the bottom is cut throu^^h and the basin becomes a hole. The bowlder is then pierced tliroui>h and becomes a riuii-bowlder. The lude is usually nearly circular on cross section,' but sometimes tapers towards the bottom. The i)ei'ii)hery or outer surface of the stone «,^enerally shows considerable irregularity, for the hole is seldom symmetrically placed. Otherwise these bowklers have tlie common sub-angular form. Pierced or ring-bowldeis are the highest type (»r variety of the several forms produced by scour. They are scarce, even where other lower varieties are abuiiilant. Only one was found on the course of the ancient outlet river within the Mattawa valley, and ibis lies in such a position and at so low a level with reference to the modern river that it i)rol)ably was made by it. This ring-bowlder lies in a side channel at Parasseux ('In'irc A dam was constructed across the head of tliv' rapids several years ago and this left a si(le channel east of the pre>eiit rapids ^\v\. h\ the bottom of this channel about oj)posite the middle of the present rapids below the dam lies the ring-bowlder. It is broken in two pieces, but they are se|)arated only a few inches and their former solidity as an unbroken ring is at once obvious. The hoi e is not perfectly circular, but has a large diameter com- pared with the diameter of the i)owlder itself. The hole is about eighteen inches across, while for about one-third of the circumference the ring of rock is oiilv six or seven inches thick. Put the most magniticent specimen of this variety that the writer has seen is on the bank of the Ottawa river near Klock's, ten miles below Mattawa. This bowlder is large — about seven feet long, five wide and four thick. The hole is "^K Taylor— Scouml BoirUerH of the Mattaim Valley. 213 iil)out cifrlitccn or twoiity inclies across at tlio top, l>nt tapers to ahoiit liiirlit or ten iiiclios at the bottom. TIh' Itowldcr lias ovi- (Iciitly been sli;;htly tilted since it wa.s hored out, and may, ip.decfl, have Iteen moved a ('(Uisiderahle distaruie. It lies at the ed<,^e of the water a tew n.ds up stream from the residence of the Hon. .lames H. Kh.ck, and is readilv visible oidy at U)W water. From the Itev. E. Maerjab of jVfattawa the writer learned of another riiiir-bowhU'r wliich may be seen on tlie bank of Lake Temiscamaiii; at the narrows at oM Fort Temiseamanir near Jiaic des Peres. In this case a tree <,'rew up thronjrli the aper- ture and finally broke the bowlder in two. The stone was literally strung; on the tree. liiiHhfd bowlders are much more numerous. They are fairly abund:int in the rapids of the ancient outlet at Des Ep'ines rapid's and at \rattawa and also in several of those of the inodern Mat- tawa and OttJiwii. They exist in all sta.d evidently received its marks of scour In situ. This was the case with the great bowlders especially. In the case of many small bowlders, however, the worn cavities may have had a different origin. If a small bowlder had a small sliallow basin worn on its top and then had been turned over on its side, the basin would then have the appearance of a true niche. No doubt many have had tin's origin. But in several instances it was plain that the niche lu'd been worn while the bowlder was in exactly the same position as to-day. Am. Jour. Soi.— Fourth Series, Vqi,, HI, No. 15.— March, 1H9" 15 214- Tdijlor — Scoured BovMers of the Mattawa Valley. m Shallow, sinootli-woni hollows are often found on the slant- ing; sides of l)o',vlders, and sometimes on stones no larger than a foot in diaiiieter. The orifjin of such forms can seldom be made out with certainty unless it is clear that the stone has remained unmoved. In a few cases two bowlders lying close together had conij)lementary grooves or hollows in them. Probably nearly all true niches were caused by the diversion of the current by one bovv^lder so as to strike the side of another. Gutteieil bowlders in typical form are almost as rare as ring- bowlders. It requires a bowlder having considerable tiat or nearly Hat surface area on its to|) to lead to the fornuition of a gutter. Hence this variety is confined mainly to bowlders of large size. The tlat surface must have some slight inequalities that will tend to guide the sand and |)ebbles which the current rolls aloTig. If these irregular features are so arranged that the weai'ing materials a-e always guided along the same path thcv' wil! finally wear it smooth and deepen it more or less, makinrocess. These bowlders may have been angular or subangular or rounded before the scouring began, and without having their general form changed they were made smooth over all surfaces alike. In the old channels where the scoured bowlders occur almost every one shows more or less of this effect. There are great numbers of scoured J)owlders along the roadside near the Presbyterian church in Mattawa and farther east for a quarter of ii mile. Near the church there are many fine examples of smoothed and basined bowlders. Some of" them are jiolished so smooth on one or more sides that they glisten a little in the sunshine even when they are dry. They have a smooth, soft feel under the hand, not like a pane of glass, but i-ather like a surface of finely embossed leather. Most of the bowlders along the road near the church have been moved in road improvement or in clearing ground for buildings. It is probable that the most highly polished parts of the best specimens were previously on the under side or buried, and so protected from the weather ever since they were polished. This suggests that numy, at least of the smaller bowlders, were turned over and partly buried during the time of the great outlet river. They were scoured and^ polished and turned over before the river'ceased to flow. It is quite possible that other forms of scour may be found on bowlders which would suggest the propriety of add- ing more varieties to the list given above. But the forms found by the author, and examined also by Dr. Bell, seem to bo fairly well covered by tiie names suggested. One other possible variety deserves'niention. When the deep cut was made through the bowldery terrace in Mattawa for the branch railroad up the Ottawa, some very curiously shaped stones were found in the gravelly to]) layer. Among others was one roughly cone-shaped', but flaring out slightly at the base. It is almost perfectly round on any horizon tarsec- Taylor — Scoured Bowlders of the Mattawci Valley. 217 tion and tapers smootlily np to a point about two inches through Its sliape may perhajxs be l)est described by saying that it is like an Irisli peasant's liat. The crown is rather pcinted and the rim projects downward and outward from it through a very gentle curve. The base or bottom of this stone is flat and smooth and showed no rough surface where it might have been detached from the solid mass. From similar speci mens seen before, the writer at once recognized this stone as the detached core of a pothole. It is about ten inches high and rather narrow and slender, and hence suggests a pothole of relatively great depth. But the edges arounil the i)ase or x.m are also apparently worn smooth. This makes it very ditticult to account fully for its origin. It seems probable that this stone was bored out of a solid bowlder. In that case it is the core left from the making of a ring-bowlder. The bowlder itself might have been smooth on its bottom before the making of the pothole began, and this would go some wa,y toward explaining the smooth bottom of the core-stone. Such stones as this might be set down as an independent variety of scoured bowlders. But so little was learned of the occurrence of this specimen that its place and manner of origin seems to be a matter of some doubt. Nevertheless its smooth and apparently fresh-polished surface suggests that it is a scour product of the rapids of the recent great outlet river. As Dr. Bell has suggested, the ring bowlder out of which this '•stone hat" or core-stone was bored may be lying close by hidden in the gravelly, bowldery surface layer (three to seven or eight feet deep), which covers that part of the terrace. Mr. Macnab pointed out another curiously hat-shaped stone on a veranda in the village. It had the sha])e of a "sou'wester," but was clearly the product of differential weathering (perhaps afterwards smoothed in the rapids) rather than of scouring by current action. Dr. Bell deposited the first mentioned speci- men in the museuin at Ottawa. Mammary, Some idea of the magnitude of the great outlet river may be gathered from the fact that at Des Ejjines rapids the mark of its upper limit is quite plain at 50 to 55 feet above the present stream, and the width of the channel at that height is between 000 and 700 feet. The average depth across the chan- nel is 35 to iO feet, and yet the current was swift enough to produce many of the finest types of scoured bov Iders. Here and in Mattawa there are other bowlder fields as. heavily cov- ered as those on which the scoured bowlders are found. But they are above the level of the ancient outlet river, and although they were examined closely no scoured bowlders were found upon thom. There are also other bowldery tracts at low levels at seii \.\X places above Mattawa. But they are situated 218 Tai/lov—Scoxired Bowlders of the Mattnim Valley, on the shores of hikes or expanded portions of the valley. Some of these too were explored, hut were found devoid of scoured bowlders. It was only in the rapids of the ancient outlet where a swift and powerful current iiov.'ed over tlieni. and where there was a supply of -ravel for the current to roll alon.'- that the higher tvpes of scoured bowlders were made. The princii)al conclusions su-jrested by the scoured bowlders may be summed up br;e«y as follows, and in these Dr. Lell is in substantial a There must have been a constant liut not too voluminous supplv of gravel or pebbles for the current to roll along over the bowldery bottom in order that the work of scour might be accomplished. . .. , , 3 Many of the bowlders, especially the larger ones, weie scoured m situ and in some cases the forms of their scour marks show clearlv the direction in which the current flowed. 4 All the indications gathered from the bowlders of the morainic terrace upon which Mattawa is built show Hiat the scourino' current came from the Mattawa valley and not from the Ottliwa. And this is true, although the best examp es relied upon for this conclusion are situated so as to be e(iually exposed to any current that might have come down the latter ^'5 'The scoured bowlders typiiied by those at Mattawaand DesEpines rapids constitute a distinct class, which has received secondary modifications of form in consequence of relatively louix continued and powerful current action. , ., , , Beds of scoured bowlders like those here described, mark- ing the iilace of rapids in great rivers no longer in existence, mJy ser^e (with due consideration of other attendant condi- tions) as valuable aids in the study of later Pleistocene history, especiallv in the bowldery Arcluean areas of the north. In the opinion of the writer the scoured bowlders ;>i-e one ot the best of several lines of evidence that clearly establish the existence of the great Nipissing-Mattawa river as the outlet of the three upper V^reat Lakes in very recent times 1 he con- clusion maintained heretofore by (Gilbert, A\ ri,ght and the author, but on evidence less complete, seems iiovv fairly proven, viz • that for a con^iderable pcn-iod of time, while this northern outlet was active, Niagara Falls was rol)bed of much the larger part of its water. Fort Wavne, Iiid.. Nov. 28. 1896. 3llis were larger I