^; >> \^l'itl|ii'il I iiTiaiyr^" b i: I ^K)E' .,:j«it ,_:.'Mi*-irimmus I <*ii ffi^-^fPf'y^'r^!^'*' ■ ►WfWt" •^WWEMWP^^- ■% '■i GLACIAL-EROSION W NORWAY AND IN HIGH LATITUDES. ON THE THEORY OF GLACIAL MOTION. By Prof. J. W. Si'KNCF.R, M.A., I'h.D., V.G.S. Reprinted from Proceedings Royal Society, Canada, 1887; and Geological Magadne (London), 1887-8; Extracted from AMKRirAN Naturalist, Vol. XXII., 188S. .1 eslSflt^ -•mi^ '*' '•*i HM »'i'1IIIMH1ipPWI»HW)f;^l)|pp— wny. i I) r I ST^i^^mvm^mf*^ _ 'A ■Btal»i4t?^ ^ V. \ 218 Glacial Erosion in Norway. GLACIAL EROSION IN NORWAY AND IN HIGH LATITUDES.' T BY PROFESSOR J. W. SPENCKR, M.A., PH.D., F.O.S. Reprinted from Proceedings Royal Roclety, Canada, 1887; and "Geo- logical Magazine " (London), 18S7-8; extracted from " Amer- ican Naturalist," Vol. XXII., 1888. I. "nURING the Slimmer of 1886, it was my good fortune to visit •^ the three largest snowfields in Norway, namely, the Folge- fond, at the head of Hardangerfjord in southern Norway, whose «rea is 108 square miles ; the Jostedalsfond, two degrees to the north, beyond Sognefjord, whose area is 580 square miles, and the largest suowfield in Europe ; and the Svartisen, extending from just inside the arctic circle for forty-four miles northward. All of these snowfields send down glaciers to within from 50 to 1,200 feet of the sea. These snowfields are not basins like those in the Alps, but are mantles covering the tops of plateaus from 3,000 to 5,000 feet or more above the tide, from which great caflons suddenly descend to the sea, and extend themselves as Qords, from 1,000 to 4,000 feet in depth. Many of the Norwegian glaciers are rapidly advancing. In their progress they do not conform to the surfaces over which they pass, but are apt to arch over from rock to rock and point to point, especially as they are descending the ice-falls. Thus are produced great caverns into which the explorer can often wind his way for long distances. Beneath the glaciers of Fondal, Tunsbergdal, and Buardal, in the northern, north-central, and south-central snowfields of Nor- way, as well as under other glaciers, I observed many stones enclosed in ice, resting upon the rocks, to whose surfaces — sometimes > Read before the Royal Society of Canada, May 25, 1887, and the American Aasociation for the Advancement of Science, New York, Aug. 1887. Printed from advanced sheets of the Proc. Roy. See. of Canada. See also "The Erosive Power of Glaciers as Been in Norway," Geol. Mag., London, Dec, iii., vol. iv., 1887, and "Ice Action in High La ti tudes," ibid., vol. v., 1888, by Prof. J. W. Spencer, M.A., Ph.D., F.G.S. n ■ ', -^saa .■iw4»i*'«*.°ii!^W-»-J«~»t» Glacial Eroaim in Norway. 219 \ I flat, sometimes sloping steeply-they adherer! by fnct.on and by the pressure of the superincumbent weight. Although held in the ice on four sides, with a force pushing downward, the viscosity of Fio l.-Section of Fon-laUbrme,.. a. bed rock; c.caveri, under glacier 6;d.loo8e ■tone; /, groove under the tee. the ice or the resistance of its molecules in disengaging themselves from each other in order to flow, was less than that of the friction between the loose stones and the rock ; consequently the ice flowed around and over the stones, leaving long grooves upon the under- surfaces of the glacier. The first observation made was at Fondals- brffien (Fig. 1), where an angular stone (Fig. 1 d) whose section was ten by eighteen inches, rested upon the sloping face of smooth rock (a) For twenty feet below the stone, the under-surface of the glacier was grooved (/) by the moulding of the ice about the obstacle. This distance showed the advance of the glacier after the stone had come in contact with the rock, for it had evidently been completely buried at the lower end of the groove, before the ice had begun to flow about it. As the ice between the stone and the rock gradually disappears, the embedded stone does not suddenly cease to move, but drags, until enough of the surface rests upon the rock to allow of friction between the two granitoid surfaces to overcome the viscosity of the ice, when the latter flows around the obstacle. Elsewhere, an example was seen of this action. Ihe knife edge of a wedge-shaped piece of gneiss was protruding beneath the ice and resting upon the rock. The front end of this stone had moved beyond the subjacent surface, while the posterior % mr — . liUmrtmHf^m » Fwni .. yjlfaii^l ^ 219 and by (1 in the 30sity of 220 Glacial EroHon in Norway. ■ b; d, loose lemselves e friction ce flowed lie under- Fondals- KJtion was ooth rock ice of the ibout the r after the jntly been ire the ice le and the t suddenly rests upon surfaces to around the ;ion. The protruding ;nd of this le posterior end was still upon it. Yet tiio sharpness of the edge had scarcely been blunted. Abundant examples were found to show that the flowing of the ice about loose obstacles was quite the rule. Both large and small (even an inch in length), angular and rounded masses, lying either upon the rock, or upon moraiinc matter, were sufficient to channel the bottom of an advancing glacier. No blocks of rock were seen in the act of being torn loose from the floor or sides of the valley, and certainly there were no loose or solid masses being picked up by the advancing glacier. PlO. 2.— Section of TmisbeisilHlsbrH'en, a. bed rock; c. ciivora under !<•« h . /# boulder; ee, moulding in Ice of the foriu of U. '^hvhu unuer ice 6 ; d. At Tunsbergdalsbrteen (Fig. 2), whose lower end is 1,600 feet above the sea, a modification of the above described phenomena was seen. A roughly rounded boulder (Fig. 2 d) of thirty inches diameter was enclosed in the convex side of the glacier, wh' :a rose above it from thirty to forty feet in height. It was resting ui on a surface, sloping at a high angle, and was held in place by the ice itself. As the surface of the stone, bearing upon the rock, was small comparetl with that held in the ice, it should have been dragged along. But it was being rolled, as shown by the mould- ing (e e) of its form in the glacier which was advancing faster than the stone was rolling down the steep slope. The pressure upon this stone could not have been merely that of the superincumbent ice a few feet thick, but also that of a powerful component of the weight of a glacier from 1,500 to 2,000 feet high descending more or less GlacUtl EvoHion in Norway. 221 m »^. like a fluid. Tlu; t'liergy upon the Ixjiilder was .sufficient to crush it into one larj^e luul two sniallcr masses, tojiellier with stone dust. "When seen, the three tVatrments had hardly l)ej:uii to part company. The abrasion of tiie solid rock by the fall of stones, and detached masses of ice and stones, was illustrated at the locality just named. The two guides and myself succeeded in detatthing a large boulder of about five tons weight, adjacent to the edge of the glacier. It went rolling and sliding down a hundred feet or more, tearing away great blocks of ice which held a considerable amount of debris, and in its wake, the rock was more or less crushed or scratched. Fio. 3.— AtTniisbermlnlshiii'fii. '/, a lortsc boulder, resting on rock ti, In cavern c, against which a tongue 7, ot liie moving ^lucles (t, IniplgeN anil is bent backward. A further example of the ability of the ice to flow like a plastic body was shown in a cavern (Fig. 3 c) 400 feet higher than the end of the glacier, where the temperature was 4°C., while that out- side was 13°C. Upon the debris of the floor rested a rounded boulder (d) whose longer diameter measured thirty inches. A tongue of ice (q), in size more than a cubic yard, was hanging from the roof, and pressing against the stone. In place of pushing the stone along or flowing around it, the lower layer of ice above the tongue had yielded, and was bent backward as easily and gracefully as if it had been a thin sheet of lead, instead of one of ice a foot thick. According to the experiments of Herr Pfaff,' the temperature of » Nature, Aug. 19, 1875 ■'^^li ^mmw MmmlHm*>—mmHt0limta 221 It to crush itone (lust, c'oinpiiny. 1 detaclied ist named. ;e boulder lacier. It re, tearing iniount of rushed or , In cavern o, backward. :e a plastic than the e that out- a rounded nches. A iging from ushing the above the gracefully ■ ice a foot perature of 222 Glacial Erosion in Nonniij. ice has a great deal to do with its flow ai)out olwtacles. Helow freozing-poiiit, the movement is .scarcely more tliaii appreciable, while above tiiat point, but not below, it may reach twenty-eight inches a day, or more. The conditions arising fnim the tempera- ture beneath the glaciers are more or less Cavorable for the move- ment of the ice, as tlie lower surfaces are never entirely below freezing-point, even in winter. Professor S. A. Se.xe ' foiind that the water flowing from a Folgefond glacier, in February, 1861, had a temperature of 1°R., whilst that of the air wa.s 7° It. below freezing-point. The .novement or flow of the ice about detached stones, rest- ing upon rocks, ha.s been ob-served by Professor Sexe beneath the Buarbra?, and by Professor J. W. Nilcs bi'iieath the Aletsch gla- cier.^ Profes.sor Sexe illustrates the moulding of the ice about a loose stone, which was held beneath the glacier by a projection of the rock. My observations were upon stones, not held up by rocky projections, but upon surfaces often sloping downward. Although Professor Niles did not recoril observations showing that there was ill f -^ -Jt-. - „mJ> %-- • ' w ii« «■* '; Olacial Kronion in Xorwai/. 223 Booii as tlie ivsiHtaiK'o diic t(» t'ri('tii»ii lu'twcoii tlic Htoiics and the rock equals tliat diii' to vmconity, whicli, as ohsprvations show, is Boon reiK'liiHl. Conscfuicntly, we slntiilil not cxiH'ct to Mud great troiiglis or grooves scooped out of solid rock hy the actual glacier. Tiiese 1 have not seen about the existing glaciers of Norway, which are not dopeiidont u|)on atmospheric and a(jueous erosion and the texture of the nx^k, although their surfaces may luivo been subse- quently polished. Generally speaking — as seen in the valley behind Fondalen Gaard, where the glacier is nearly free from sand, and contains comparatively few stones, as well as at many other places — the surfaces of the subjacent crystalline rocks, although of the form of rochea vioutonm'cs, with angles mostly removed, are not Fig. 4.— Section at Fondnlsbrseen, /i/i, zone along which Ice (b) \s llowlnu upon Its lower layers. smooth, but are as rough and us much weather-worn as similar rocks in warmer countries where no glaciers have been. Upon these surfaces, it is often difficult to discover scratches— even when present — for they are often .so faint as to be oidy rendered api)arent by moistening tiie rock. Even the face of the liummocks are com- monly imperfectly jjolished. In other places, particularly at Tuns- bergdalbrseen which contains much sand along the margin, the rocks are highly polished, and but little scratched. One is every- where surprised to find beneath the glaciers the great paucity of glaciated stones, and in many terminal moraines they are scarcely, if at all, to be found. The insufficiency of glaciers to act as great erosive agents is :t^ ^ 1 ll»W 223 ics and tiic lis show, is find great lal glacier, ivay, wliicli !)ii and the leen subse- tlie valley from sand, iiaiiy other 1 though of ed, are not ing upon Its as similar !n. Upon Hven -.vhen 1 aj)i)arent s are com- y at Tuns- argin, the e is every- I)aiicity of e scarcely, agents is 224 Glacial EroHton in Norway. farther hIiowu at Foiidaleii (Fig. 4), where a mass of ice thirty or forty feet thick abuts against a somewhat steep ridge of a rock, ten ftHit or less in height. In |)Iace of a stone-shod glacier sliding up and over the barrier, the lower part of tlie ice appears station- ary, or else is moving around the barrier, while the up|K'r strata bends and flows over the lower layers of ice (along the line hh, Fig. 4). When the barrier to the advance of a j.'lacier is met with, whether composed of hard rock, or of morainic matter, the ice, provided it be sufficiently high, flows over upon itself, yet when the sheet is no higher than the barrier, the lateral thrust may push it up some- what. The best example of the consequences of such a condition is Fig. 5.— End of Bvartisea glacier at head of Holaiidsfjurd, inovlng through n lake against morainic barrier. to be seen at Svartisen glacier (Fig. o), at the head of Holandsfjord, which descends to witliin sixty feet of the sea, where it ends in a morainic lake of considerable size, the northern side of which is filled with the glacier. The water of the lake rises, in part, to the level of the ice, or over it, where the waves of the lake are depos- iting sand upon its surface. Part of the ice is not less than twenty- five feet thick, and most of it is probably double that thickness. Some of the strata of ice are pushed up and rest at 5° from the horizontal. But the interesting points are at the end of the glacier, where it impinges against the morainic barrier. Being unable to advance, the lateral pressure has forced up an anticlinal ridge or rather dome in the ice, to a height of fifteen feet, along whose axis there has been a fracture and fault. Upon this uplifte '' * materiiU upon a toiiBue of its lee. giving snout of the glacier, just as if the l"« f"''*'* ftPPtaianoe ol a gluilal plough. ice were pushing under the boulders of earth. The glacier has a steep convex margin, from twenty to forty teet high, with many blocks and boulders upon it. These become detached, and, rolling down upon the lower tongues of ice, build up a ridge and leave a deep trough between it and the side of the glacier, and delay the melt- ing of the layer of ice beneath, which is too thin to do any plough- ing up of che moraine. An excellent illustra- tion of a glacier advan- cingjwithout any plough- ing action, over a mo- raine, and at the same time levelling it into a sort of ground moraine, Fig. 7.-End of Supliellebrseen advancing over a wassecnat Suphellebrseen '""'*'"*'• (Fig. 7). Here the gla- cier was moving up the slight elevation of a moraine produced by the early summer retreat of the glacier, although again advancing in July. The lower surfaces of thp ice-tongue were furrowed by the loose stones of the soft incoherent water-soaked moraine, into which one's foot would sink when stepping upon it. The moraine was being levelled by the constant dripping of the water from the whole under-surface of the advancing glacier. The glacier of Suphelle is the most remarkable of its kind, being a gigantic glacier rimanie. From the Jostedalsfond, which, near 225 ^'ey sand were lis the appear- 226 Galcial Erosion in Norimy. )nsltliig morainlo of its li-e, giving , glHclHl plougli. cier has a steep 1 many blocks , rolling down I leave a deep lelay the melt- .0 any plough- ellent illustra- glacier advan- )utanyplough- 1, over a mo- at the same lling it into a ound moraine, Suphellebrseen Here the gla- e produced by ;ain advancing e furrowed by [ moraine, into The moraine water from the its kind, being id, which, near \ I the head of the valley of Fjierland fjord, is 3,000 to 4,000 feet high, the clear, bluish ice fiills over a precipice of dark rocks for about 1,000 feet, and at about 1,500 or 2,000 feet above the sea begins to re-form into a glacier extending down into and nearly across the valley of Fjserland for a distance of somewhat less than a mile, to a level of only 175 feet above the sea. The glacier is much crevassed, and covered and filled with debris. In fact, it was the most dirt-laden glacier seen— not excepting the Aar glacier in' the Alps. This material is wholly derived from the side of the moun- tain, and is brought down by frosts, and more largely by the fall of ice as it dashes from one frost-cracked rock to another. One of these great ice-avalanches I witnessed from the other side of the valley, fully a mile distant. Thousands of tons must have fallen at this time, but as the ice fell from rock to rock, it was con- verted into what, seen at the distance, appeared to be white dust. There arc no considerable streams from the upper glacier, but from the rapidly melting glacier below the fall the volume of water laden with mud is large. As this glacier is not ploughing up, but levelling down the inequalities of its bed of loose material, we cannot suppose that the mud comes from any other than the dirt upon and within the ice, and that obtained by the dripping water as it levels the terminal moraine. This is only one of the examples everywhere to be seen showing the erroneous estimate of glacier- erosion, when based upon the amount of mud carried down by the streams flowing from the glaciei-s ; for the debris is brought ujwu their surfaces by otiier than grinding action, and, as far as observa- tion goes, it is not derived from beneath them, at least, to any great extent. Although I have seen some of the sharp angles of the rocks at 2,000 feet above the ijords along the sides of the valleys, some- what rounded and scratched, yet the inequalities of the faces have not been removed by erosion of any kind. At numerous placies in Norway, as well as in other countries, hummocks of rock rise above or out of the glaciers, as the ice flows around them at lower levels, these channels having been deepened, not by glaciers, but by sub glacial streams. Nowhere are the roches moutonnees so abundant as on the coast of Norway. In their more perfect form, they are not extensively developed along the coast at more than 250 feet above the sea. A -=^.-«ift'^-i^? r<=^4;#F^ 2t^ -^SJi>-»'ijji>£>^sr«a*^,-(rvlS^-wrt.i,. ;:i fi ,\ y t 6(1 Glacial Erosion in Norway. •227 higher altitudes they are best seen about ghicier-falls, farther up the valleys. But (hu'iug the Pleistocene clays, the coast has been raised several hundred feet, at least. The form of the hununocks is precisely like what may be seen in southeastern Missouri and other States south of tho line of northern drift, or are described as occurring in Ceylon, Brazil and other tropical countries, to which only are added the scratches. The forms of these hummocks must bo principally attributed to the atmospheric erosion of the crys- talline rocks where the debris has been swej^t away by currents or by ice. We see them more frequently swept clean upon the coasts of either cold or warm countries than in the interior, where the currents are only those from rain or local glaciers, for even the sweeping beneath the glaciers is principally effected by drip- ping waters or streams. Professor Kjerulf, of the University of Christiania, than whom there is no better authority, regards the production of hummocks and their glaciation up to a height of 600 feet upon the coast of Norway, as the result of floating ice.' The absence of transported boulders and striations upon the sur- face of many parts of the high plateaus of Norway is doubtless, in part, attributable to the ability of ice to flow around loose obstacles, and the frequent want of higher ridges to furnish material by their debris falling upon the ice to work through the mass afterwards. The faith in glaciers, as great erosive agents, has been so severely shaken that few geologists, who personally study those still exist- ing, now attribute to them greater power than that of removing soft materials, and of this power many others are sceptical, e.g., Pro- fessor Penck,^ of the University of Vienna, who has been mis- quoted as having proved their great efficiency in eroding basins in hard rocks. To this scepticism, it seems to me that these notes must contribute; especially when glacial erosion is applied to the hypothetical excavation or modification of great lake-basins, and the transportation of the northern materials in the boulder clay ove the broad plains of America, as there were no mountains of ade- quate height with peaks, or seracs, to supply the detritus sufficient to furnish the tops of the glaciers with all the boreal material of the drift, which " covers half a continent." Discourse before Meeting of Suandiiiavian Naturalists, Copenhagen, 387S. ' Geological Magazine, April, 1883. •^ m 7 227 , farther up ist has been hummocks issouri and I escribed as is, to which nocks must f the crys- by currents II upon the jrior, where s, for even ed by drip- iiiversity of regards the jiglit of 600 ice.' )on the sur- loubtless, in se obstacles, 'ial by their terwards. so severely still exist- if removing il, e.g., Pro- been rais- )g basins in these notes plied to the iins, and the er clay ove lins of ade- us sufficient material of !openhageD, 228 Glacial Erosion in Norway. In connection with this paper, the observations of Herr Payer and other arctic explorers are important. The snow-line of Franz Joseph Land descends to within a thousand feet of the sea, and the numerous glaciers discharge great quantities of icebergs as they move down into the ocean. Payer says : " However diligently I look for them, I never saw unmistakable traces of grinding and polishing of rocks by glacier-action."* Lieutenant Lockwood ^ found in central Grinnell Land a thick ice-cap, extending for a distance of from seventy to ninety miles* faced by an ice-wall of from 125 to 200 feet high, irrespective of topographical inequalities. It was free from rock debris, except in a valley confined by mountain-walls thousands of feet high. Along its foot there was almost an absence of morainic deposits, and even where present these were unimportant ridges. Tiie general absence of rock and dirt in the arctic glaciers is a common subject of remark. The snow line in the high latitude of central Grirnell Land is 3,800 feet above the sea, and the glaciation of the rock about the adjacent Lake Hazen (500 feet above tide) is not recent. In Spitzbergen, where the snow-line is much higher, striated rocks, according to Nordenksjold, occur only below 1,000 feet.' The same holds true for Labrador, where the scratches are confined to the lower thousand feet, although the mountains rise to 6,000 (Bell).* In the Antarctic regions, the officers of the "Challenger' remarked the absence of detritus in the icebergs and southern ice, although Wilkes and Ross saw rocks upon a few bergs. These last are supposed to have come from valleys in the volcanic moun- tains. Indeed, outside of valleys, explorers in high latitudes have not found, in the margins of such ice-caps visited, the tools capable of great erosion. The continental area of North America presents vny much lower and less abrupt prominences than the reliefs of Greenland, Grinnell Land, Spitzbergen or Franz Joseph Land. Overhanging mountains seem to be necessary to supply glaciers with tools by which alone any abrasions can be accomplished, and > New Lands within the Arctic Circle, 1872-74. « Three Years of Arctic Service, 1881-4, Greely. * 8ee Geological Magazine, 1876. « Dr. Robert Bell, in Hudson's Bay Expedition <.f 1884. L LV^ -•S'it^ ^*^"**S5hl*v^^^'!a!»J*flrti^-ii**45h»^^ ■^*ir'''^.^"r.iiimi/.» : '. fc»n^--i,^-» r«»J%,-., , t I ») Glacial Erosion in Norway. 229 these conditions belong only to valleys of great mountain ranges. However, there is one condition under which glaciers, when shod with graving tools, ought to be great eroilers, viz., when their motion is much more rapid than the flow of land ice, — which si -almost invariably less than three feet a day, under which condition, included stones commonly adhere by friction to the subjacent rocks, and cause the lower surfaces of the ice to be grooved. This condi- tion of extraordinarily rapid movement has been seen at Jacobs- havn glacier in Greenland, where Professor Helland * found a velo- city of from forty to sixty feet a day. In Alaska, Lieutenant Schwatka^ and Professor G. F. Wright' observed glacier move- ments of from forty to seventy feet a day. In these cases the-gla- ciers are moving into the sea, and the new element of partial flota- tion or sliding, which does not belong to land glaciers, is here intro- duced. The great velocity of these glaciers is far beyond any observed ability of ice to flow as plastic bodies ; consequently, one is led to conclude that, under partial flotation, stones may be held firmly as graving tools by glaciers. Hereby we are able to explain the oreurrence, in many Alpine valleys, of a greater glaciation than we see in progress to-day, as being due to glaciers rapidly advancing into Qords, during a period of j>artial submergence. The appeal to the greater magnitude of the glaciers, as produc- ing eflects not now seen as the result of those of the present day, seems to be begging the question, for the action of thicker glaciers differs from that of thinner in amount rather than in kind ; for increased pressure, raising the temperature, increases the plasticity of the ice, as it is seldom if ever lower than freezing point. Con- sequently it seems improbable that stones should be held more firmly in glaciers of thousands of feet in thickness than inlthose of hundreds of feet. In addition, the friction between the stones held in the ice, and the surface of the subjacent rock, is proportionally increased by the greater weight of the glacier. Over the vast area of action, the work of floating or sea-ice, in some forms, is enormous. On the northern side of Hudson Strait ' Ice-fjords of North Greenland, Quart. Jour. Geo. Sec, 1877, A. Hel- land. ^ "Times" Alaska Expedition, New York, 1886, Schwatka. » The Muir Glacier, Am. Jour, of Bel., 1887. S-.-^'^^MfattJilii- 229 aln ranges, when sliod /hen their , — which si 1 condition, icent rocks, rhis condi- 1 at Jacobs- und a vek>- Lieutenant icier move- sea thegla- artial flota- I here intro- )eyond any uently, one lay be held any Alpine 3 to-day, as ng a period as prodnc- )resent day, ker glaciers I kind ; for le plasticity aint. Con- held more inlthose of stones held portionally ' sea-ice, in [Ison Strait 877, A. Hel- ka. > 230 Glacial Erosion in Norway. Dr. John Rae,' who had very extensive arctic experiences, found that snow drifting over precipices into the sea resulted in the for- mation of bergs, sometimes a hundred feet thick, filled with the loose rock debris of the coast, and having the form of the shore where formed. Most of them break loose and drift away to melt or become stranded elsewhere. Greely describes the great momentum with which the Hoe-bergs come together. By their meeting the ice is crushed, and raised up into ridges fifty or sixty feet high. One cannot read carefully the results of the British Arctic Expe- dition of 1875-6 without being impressetl with the erosive power of drifting ice, moving with a velocity never acquired by glaciers. Floe-bergs are pushed upon a shelving sea-bottom, until the ice has risen from twenty to sixty feet, after their first stranding in perhaps only from eight to twelve fathoms of water, although weighing tens of thousands of tons,^ As the grounded floe-bergs are forced up the shelving sea-bot- toms, ridges of earth and stones are pushed up in front of them. Floe-bergs which have been toppled over, thus showing their orig- inal bottoms, and also masses of pushed-up coast ice are found to be grooved and to contain angular stones with their exposed sur- faces scratched and polished. As the movement is greater than the velocity of glaciers flowing about obstacles, it is only natural to expect that the enclosed stones should be held firmly as graving tools, or be wrenched out owing to the brittleness of the ice under such great stress. In describing the ice action on the coast of Labrador, Professor H. Y. Hind says the " pan-ice " (from five to twelve feet thick) is polishing the surfaces and sides of the rocky coast, and producing boulder clay. He says : " When the pans are pressed on the coast by winds, they accommodate themselves to all the sinuosities of the shore line, and being pushed by the unfailing arctic current, which brings down a constant supply of floe ice, the pans rise over all the low lying parts of the Islands, grinding and polishing exposed shores, and rasping those that are steep-to. The pans are shoved over the flat surfaces of the Islands, and remove with irre- sistible force every obstacle which opposes their thrust, for the ' In Canadian Journal, Toronto, 1859. ' British Arctic Expedition of 1876-76, Sir George Nares. i \ .■-,--^'>:--'>^mmsm^mJt'r^^^''**<^*'^9^m mi>< m nu» <-<'m,''s^^ -,.-i^- ,-'*>■>«— -- Glacial Erosion in Norway. 231 attacks are constantly renewed by the ceaseless ice stream from the northwest, and this goes on uninterruptedly for a month or more." ' Similar results elsewhere have been frequently recorded, as those of Professor Milne in Newfoundland.* While the power of glaciers, under favorable conditions, *o abrade and scratch rock surfaces, as "sand-paper" scratches "a cab- inet," is not questioned ; yet these observations, in Norway and else- where in high latitudes, all confirm the correctness of the verdict given by many geologists — especially in Europe — who have had the opportunity of personally studying living glaciers, that the potency of land-glaciers to act as great eroding agents, capable of _ " planing down half a continent," or ploughing out great valleys, or lake-basins, or even of greatly modifying them, is not only not proved, but most strongly negatived. Even the power of glaciers to abrade is reduced in many cases almost to zero. ' Notes on Some Geological Features of the Northeastern Coast of Labrador, Can. Nat. 1878. " Ice and Ice Action, Newfoundland, Geol. Mag., 1876. itsc" 't W W tf i i^ 231 n from the or more." * as those of iditions, *o lies " a cab- ly and else- the verdict. have had i, that the capable of eat valleys, »t only not of glaciers rn Coast of ON THE THEORY OF GLACIAL MOTION. As the foregoing paper contains some observations bearing npon the character of glacial motion, the correlation of these observations and a short consideration of the latter snbject tbrms an appropriate ^" As^Xders disport themselves like rivers, in that they are con- sUmtly flowing, with greater vel.K^ity at their centre than their mar- gins, above than below ; tvs they form pools and rapids, an( contorm themselves to ehamiels, Prof. Forbes was led to propose the theory that- " A glacier is an imperfect flnid or viscons body which is urged down slopes of a certain inclination by mutual pressure ot its parts." ' He explained the veined structure of glaciei-s an being due to the diiferential movement of its parts. Against this view, it was urged that ice is a brittle solid, which in the laboratory cannot be moulded as a semi-fluid or even in nature, when in passing over a change of ^eclivity of even 4, it becomes ruptured. Consequently, Prof. Tyndall applied lerature, which expansion Dr. CroU* modifie