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Scottish Geographical Magazine Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rsgj19 The Dumbartonshire Highlands H.M. Cadell B.Sc. a a H.M. Geological Survey of Published online: 30 Jan 2008.

To cite this article: H.M. Cadell B.Sc. (1886) The Dumbartonshire Highlands, Scottish Geographical Magazine, 2:6, 337-347, DOI: 10.1080/14702548608554487 To link to this article: http://dx.doi.org/10.1080/14702548608554487

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Great Britain may wisely demand that the most-favoured-nation clause in our treaty be carried ou% so as to give us an equal share in the foreign affairs of the island ; our Foreign Office may wisely consider our consular service as being inadequate and defective. Until these things are done, my advice to capitalists would be "Leave it alone," as the l%ench "seek to root out the English influence,.... by every means in their power," in these islands.

THE DUMBARTONSHIRE HIGHLANDS. BY H. M. CAI)ELL,B.SC., ELM. Geological Survey of Beot~a~tg. AREA. The Dumbartonshire Highlands, rising in rugged grandeur all along the western shore of Loch Lomond, are well known to lovers of Scottish Scenery. The county boundary enters the loch by the mouth of the river Endriek, near Buchanan Castle, and, undulating northwards among the islands, follows the central line of the upper and narrower reaches as far as Island I Vow, two miles below Ardlui. At this point it strikes east, and runs from the loch to the top of Beinn a' Choin (nearly 2600 feet high), where it resumes its northerly course, running along the ridge between Loch Lomond and the head-waters of the Loch Katrine valley. Trending westwards, across Glen Falloeh at Inverarnan, it pro- ceeds towards the head of Glen Fyne, encircling Ben Vorlich and the bleak granite plateau beyond Loch Sloy. It then wheels southwards along the dark ridge of Ben Dhnbh and Ben Vane, and passes by Coire- grogain Burn and Glen Loin, into the head of at Arroehar. The parish of Arrochar is the ancient country of the "Wild Macfar- lanes' plaided dan." Their gathering place was the shore of Loch Sloy, a wild sequestered mountain turn about a mile in length, which lies in the bottom of a deep defile, on either side of which the dark and rugged precipices of Ben Vorlich and Ben Vane rise to heights over 3000 feet. But as this northern corner of Dumbartonshire is most intimately con- nected, from a physical point of view, with the Highlands of Argyllshire, and can hardly be described apart from these, I shall mainly confine my

Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 attention to that part of the Dnmbartonshire IIighlands which lies to the south of Ben Vorlich. Most of the region now referred to was formerly the country :of the Clan Colquhonn, and is at present owned by the chief of the clan, Sir James Colquhoun of Rossdhu and Luss. The are~ is almost entirely comprised within the 1-inch Ordnance Sheet 38, which extends southwards from Ardlui to Ross Priory, and westwards as far as Garelochhead. In my description reference will, however, be made to the neighbouring country to the west and south, included within Sheets 37, 29, and 30 respectively. The accompanying panoramic sketch was taken from a point near the top of Ben Crois (2785 feet), on a clear day last October, and will serve to YOL. II. Y 338 THE DUI~IBARTONSHII~E :ftIGHLANDS.

convey an idea of the shape and character of the Dumbar~onshiro High- lands south of Ben Vorlich, and the country to the south and east. The range of country commanded from this point is extensive, stretch- ing as it does from Arran, on the south, to the Renfrew, Kilpatrick, and Campsie ttills and Stifling Castle, in the far east, with Loch Long and Loch Lomond inthe middle distance. The Dumbarton Highlands south of Ben Vorlich occupy a clearly defined triangular area between Loch Lomond and Loch Long. The apex of the triangIe is at Upper Inveruglas, a hamlet on the shore of Loch Lomond, three miles above Tarbet, and in line with the valley of Loeb Long. Strone Point, at the mouths of Loch Long and the Holy Loch, may be taken as the western end of the base, and BalIoch at the foot of Loch Lomond as the eastern. The Loch Lomond side of the triangle has a length of about 18 miles, and the western, or Loch Long side, a length of 20 miles ; while the distance, as the crow flies, between Balloch and Strone Point is 12 miles. The mountainous region of which I propose chiefly to speak, has thus an area of about 110 square miles. As Loch Lomond is only some 30 feet above mean sea-level, a sub- mergencs to that amount would convert it into a typical fiord like Long Long. A further subsidence of 100 feet would permit the sea to overflow the narrow isthmus between Tarbet and Arrochar, and sever the Dum- barton Highlands from the mainland.

!VIOUNTAINS.--In the admirable papers which Professor Geikie has from time to time written for this .~agazine, the intimate connection between geology and geography has been well brought out. The exist- ence of this relationship cannot be too Strongly insisted upon ; for without some knowledge of physical geology it is quite impossible to understand the why and wherefore of the shape of a country, the architecture of its mountain masses, and the origin of its river system. All the rocks of this and most other parts of the belong to the "~etamorphie Series "--that is, they have at some remote geological period been metamorphosed into something different from what they were at first. Whether this alteration was produced by heat, pres- sure, mechanical or chemical processes, does not concern the present

Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 inquiry. It is sufficient to note tha~ the metamorphosed rocks occur in beds or thin laminze, with a regular inclination and outcrop like ordinary stratified deposits. Between Luss and the Gareloch, the country is made up chiefly of clay-slate, which is extensively quarried at Luss, and was formerly worked at Roseneath also: Further north the clay-slate gives place to mica-schist --a formation very widely distributed over the Highlands. The general strike or direction of the outcrop of these rocks is W.S.W. and E.N.E., a stl~cture which, as we shall afterwards see, has had an important modifying influence on the river system. Between Loch Lomond and Loch Long the mountains are, as a THE DUMBARTONSHIRE HIGttL&NDS. 339

rule, distributed in a series of rudely parallel ridges, with a general trend to N.W. or N. They cannot, therefore, have been elevated by the same forces as those which tilted up the rocks below, since they cross the edges Of the strata at right angles, in much the same way as the ridge of a roof crosses the gable walls. They are, in fact, all typical "mountains of eircumdenudation," and have been carved and moulded into forms altogether different from those they would have assumed had they been the results of flexures and dislocations of the earth's crust. It is hard, indeed, for the non-geologist to realise this fact. Standing on some peak that overlooks the billowy expanse of bens, he finds it difficult to believe that all those deep glens and misty corries have been quarried out of a primeval table-land. And yet such is the simple fact-- rain, frost, glaciers, and running water are the tools which Mature has employed in fashioning the existing surface-features of this region, ttere, if anywhere, we may learn what is meant by the term "geological time." Think of the ages required for the gradual removal in the form of gravel, sand, and mud of the Vast rock masses which once occupied those ravines, glens, and open valleys! From such a conception the mind naturally recoils, and would fain take refuge in any other explanation which requires less imagination to grasp. It is only after long and patient study, and careful balancing of all the evidence, that we begin to appre- ciate the stupendous effects of denudation, and are driven, it may be against our will, to see that, whether we can fully grasp the conception or no, our Scottish valleys are ~ot gaping rents in the earth's crust, nor our mountains the results of direct upheaval, but that all these surface-features have been produced by the same agents as are busy around us at the present time. The mountains between Loch Lomond and Loch Long, as shown on the sketch, are generally massive in form and lacking in individuality of outline. There are here no rugged peaks towering, like Ben Lomond, head and shoulders above their neighbours, or curiously carved pinnacles,

like Ben Arthur and the Cobbler on the opposite side of/ Loch Long. The mountains have, on the contrary, a very uniform height, and are seldom markedly Precipitous. Between Tarter, Luss, and Garelochhead distinctive names have been given to the twelve principal eminences. Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 These are all over 2000 feet in height, and have an average elevation of about 2200 feet. The summits exceeding 2300 feet are all clustered round the head-waters of the Luss River, within a circle three miles in diameter. The names and heights of the twelve are as follows :- Feet. Feet. Donne Hill, . 9.409 Ben Reoch (brindled), . . fl168 Beinn Chaorach (sheep), 2338 Mid Hill, 2149 Beinn a' Mhanaish (~vhite), • 2328 Beinn Tharsuinn (transverse), 2149 Beinn Eich (horse), . 2302 Beinn Dubh (black), 2108 Crunch An't Sithein (Fairies' Balcnock (hillock hamlet), . 2092 Stack), . 2244 Tullich Hill, . 2075 Beinn Bhreac (spotted), 2233 340 TtIE DUI~_BARTONSHII~E HIGhLAnDS. RIVER S¥STE~.--To the physical geographer, the river system of this part of Scotland is more interesting than the mountain architecture. On glancing at the map, two prominent facts at once strike the eye. The first is that all the main rivers flow in an easterly or south-easterly direction, and the second, that the water-partings are situated not midway between, but close to the eastern sides of the principal valleys. This phenomenon is strikingly exemplified both in the Dumbartonshire High- lauds, and in the district of Cowa]l between Loch Fyne and Loeh Long. In the Dumbartonshire Highlands there are three principal lines of drainage--Glen t0ruin, Glen Luss, and Glen Douglas. Glen Fruin (" the valley of sorrow") is the largest and most southerly of these. The Fruin Water rises on the Maol an Fheidh ("rounded hill of the deer") the southern shoulder of Beinn a' Mhanaich, near Gareloehhead, and flows south-east- wards for 6 miles, then due east to Loeb Lomond near Arden. This stream, whose source is only about a mile from Garelochhead, and two miles from L0eh Long; instead of running, as might be expected, into either of these arms of the sea by the shortest course, has been urged by some mysterious impulse to flow in the opposite direction, although its journey is thereby lengthened t6 I0 miles. Glen Lass has in the same way been trenched right through the heart of the highest group of bens ; and the Luss ~ra~er, strange to say, is fed by streamlets flowing from the weste~ slopes of Beinn a' ~Ihanaich, above Loch Long. The total length of the Luss River is 6 miles as the crow flies, and the distance between Loeb Lomond and Loch Long, measured along the same line, is 7 miles. The water-parting is therefore only a mile from the western valley, but 6 miles from the eastern. The third and smallest of the three rivers is the Douglas Water. 1 It follows the same rule as the others, rising, partly behind Creagan Hill and partly on Tullich Hill, about half a mile from Loch Long, and flow- ing easgwards through Glen Douglas to Loch Lomond, 4½ miles from the watershed. In the district of CowM1, in Argyllshire, the mountains are higher, the drainage area larger, and the quantity of water to be carried off greater thaza in the Dumbartonshiro Highlands. With the exception of the Kinglas Water, near the head of Loch

Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 Fyne, no considerable streams join that large fiord from the east. The drainage is conducted along three main channels, tWO of which pass into Loch Long, while the third joins its seaward prolongation. If we could suppose the land to dse till Loch Goil, Loeh Long, and the Holy Loeb became separated from the sea, and converted into ordinary river valleys, we should have as the fil~t large tributary to the Loch Long river, a stream

i This stream is not called after the Lowland family of the same name, as the spelling might lead one to suppose, but is derived from the Gaelic dubhghlas, or dark grey, a common and descriptive name for Highland waters. It should be spelt DugIas, and pronounced Dooglas--a sound both pleasanter to the ear, either of the stranger or the Celt, and less misleading to the philoIogical student. THE DUtVIB~kRTONSttIRE tIIG/:ILANDS. 3~1

rising 1~ miles from the Loch Fyne valley, and flowing S.S.E. for 10 miles through Hell's Glen and the channel of Loch Goil. The river Cur--the second main tributary--which drains the country south of Loeb Goil, after a steep mountain course of 4 miles, reaches a point near Straehur less than 150 feet above sea.level, and only a mile from the shore of Loch Fyne. Urged eastwards by the same apparently inscrutable principle, it wheels to the left, and, turning away from Loch Fyne, winds through the mountains along the bottom of the deep defile of Loch Eck, joining the Loeh Long Valley at the mouth of the Holy Loch, It miles from the turning-point. The third considerable stream of Cowall is the Ruel, whose head-waters rise on Crunch Mot (" great stack ") above Castle Lachlan, and about 2 miles from Loch Fyne. The Rue1 runs through Glendaruel in a S.S.W. direction, nearly parallel to Loch Fyne, bat seems to try, if possible, to flow east- wards like its neighbours. In this it has only been partiMly successful, since by tire time it reaches the sea at Loch Ridden, between the Kyles of Bute, it has not managed to cross the meridian line, but flows along a valley with a due north and south trend. The valley of Loch Striven between Loch Ridden and the Holy Loch is not so long as either of the others, but supplies an equally good example of the generM principle which seems to rule the trend of-the drainage glens of Cowall. In studying the rivers of this part of Scotland, we must not forget the Forth, the largest of them all. The Forth flows in the same general direction as the streams of Dumbartonshire and . Its water- parting is the ridge on the east side of Loch Lomond, and the edge of the Forth basin sometimes comes within two miles of the luke margin. Every why has its wherefore, and for this peculiar behaviour of our streams ~here must be some reason, could we but find it out. With the help of a little elementary geology, the cause may be hopefully sought. The fact that all the rivers run in the same general direction proves that at some period the general slope of the land was in this direction also, since wager, like other forms of matter, obeys the law of gravitation, and flows from a higher to a lower level by the shortest possible path. The first rills which trickled over the surface of the primeval table-land would flow straight down the slope, and would begin to cut out ruts and channels under the sole guidance of gravitation. Were the plateau per-

Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 fectly homogeneous in texture, the streams would retain their original courses as they continued to eat their way downwards into the rock. ]3ut this has not been the case here. The materials to be cut through were very variable in: s~rength and durability, and sometimes the streams encountered hard strata, through which they had great difficulty in sawing their way. The strata were moreover not only very hard at places, but they were also so inclined as to offer much resistance to erosion along particular Hues. To illustrate by a homely example the way in which the internal structure of a country might influence the river system, let us take a fir board, say a yard 10rig, and half a foot broad, and draw the point of a 342 THE DUlVIBARTONSHIRE HIGHLANDS. nail diagonally across it. A difficulty will soon be experienced in drawing a perfectly straight rut between the opposite corners of the board, as the point of the nail will always tend to work round and run parallel to the grain of the wood along the direction of least resistance. If drawn without the help of a straight-edge, the line thus traced will consist of a series of irregular zigzags--the result of a struggle between the draughts- man's hand and the lateral resistance of the fibre of the wood to a point dragged obliquely across it. Under such circumstances the difficulty in drawing a strcdght line is directly proportional to the acuteness of the angle between the direction of the moving point and that of the fibre. As the angle approaches 90 ° the lateral resistance obviously vanishes, and there is no difficulty in drawing a perfectly straight line square across the board. Now, between the fir board and the primeval plateau there subsists a certain analogy, in so far as each is built up of laminm or strata with different degrees of hardness. The laminm, whose edges resisted the oblique motion of the nail, are layers of wood added to the original tree year by year, and the laminm of the plateau are beds of rock, the edges of which crop out and give the surface a banded or stratified character. If now, instead of trying to make a rut:by drawing a gigantic nail obliquely across the edges of the strata, we watch a stream cutting out its channel in the same direction, we shall find a deflecting process going on precisely analogous to that experienced before, gravitation being here the direct moving force. Viewed in this light, the river system of the Dumbar~on Highlands is not so arbitrary as might be at first supposed. The main lines of drainage have all been drawn by Nature's Architect on a perfectly definite plan, and the valleys have been quarried out under the influence of laws more unchangeable than those of the Modes and Persians. In nearly all the older lines of drainage there is dear evidence of a struggle at some remote geological period between the action of two forces. On the one hand, gravitation was constantly drawing the streams onwards from higher to lower levels, and trying to bring them as soon as possible to their destination. On the other hand, the upturned edges of hard strata, crossing the direction of slope obliquely, t.ended to deflect the Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 waters, and cause them to turn aside from the straight and shortest path. In some cases there has been no such struggle, because the strata may have been flat, or so inclined that their edges either crossed the direction of slope at right angles, or entirely coincided with it. Here, there would obviously be nothing to prevent the water from keeping to its original path. Although many of the river valleys have been thus modified by the geological structure of the ground, it is improbable that the original direction of the water-parting of this part of Scotland has been greatly altered. The present watershed crosses the country in a general N.E. direction, and the rivers consequently flowed at first towards the S.E. THE DUlYIBAI~TONSHIRE HIGHLANDS. 343 In the Dumbarton Highlands the principal waters have a general south- easterly or east-south-easterly course. The river Luss, however, does not run throughout its entire length in this direction, but is divided into three parts, of which the first and last alone conform to the general rule. The central part has an E.N.E. trend, parallel to the strike or direction of outcrop of the rocks over which it flows. This zigzag in the valley is a good illustration of the modifying influence of the strata when found crossing the line of a stream obliquely. A glance at the map will show that the upper part of the Lass valley is exactly in line with the Finlas, a smaller stream which drains the high ground between Luss and Glen Fruin, and enters Loch Lomond at Rossdhu. This may be merely a coincidence ; but to me it seems more probable that at an early stage in the development of the river system, when the bottoms of the valleys were 1500 feet higher than now, the two streams may have been united in one straight channel six or seven miles long. Gradually ¢,he ridge of Beinn Tharsuinn (" the transverse ben") began to stand out and to obstruct the south-easterly flow of the river. The upper waters, beginning to be thus dammed back, travelled along the strike of the rocks in search of another outlet, and, finally, made good their escape into Glen 1Vfallochan, the next valley to the N.E. The new cross valley between the ancient Glen Finlas and the ancient Glen Mal- 10chan was gradually deepened, and at last the upper part of the :Finlas ceased to discharge into what is now Loch Lomond by its old channel, but became converted into the main tributary of the Mallochan. The remain- ing part of the old Finlas, fed by the little streams on either side, continued to flow along the ancient glen, and the intervening ridge of Beinn Tharsuinn, now beyond reach of the rivers, has suffered compara- tively little erosion. As the tributary was larger than the part of the Mallochan above the confluence, it deepened its bed to a correspond- ingly greater extent, and instead of being a tributary any longer, became the principal river the Lass Water. The present Mallochan, therefore, I regar4 as only the upper half of the ancient stream which occupied the same channel. In the district of Cowall the slates and schists are highly inclined, and have a general strike to ~T.~T.E. parallel to the long peninsula of Kintyre.

Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 In flowing towards the S.E. the streams will therefore cut the edges of the strata obliquely, and will be constrained to flow in a more southerly direction than they would do under the influence of gravitation alone. The first evidence of the struggle which has here taken place is seen in the Loch GoiI valley. This glen begins in the normal S.E. direction, but is deflected to the south for about three miles before again regaining its old course previously to joining Loch Long. The southern part of Loch Eck supplies a second and even more interesting example of the same phenomenon. In this valley there is also a case precisely similar to that of Glen Lass and Glen Finlas. The valley of the Cur, including the upper part of Lock Eck, trends to S.E. If the line of this defile be pro- 34~ THE DUMBARTONSItlRE I-IIGI:tLANDS.

duced to Loeh Long, ,it passes along the centre of Glen Finart, in exactly the same way as the line of the upper part of Glen Lass passes down Glen Finlas. Again, if the llne of the Holy Loeb be prolonged to N.W., it coincides with the line of Glen Massan, precisely as the lower part of Glen Luss, when produced, passes up Glen Mallochan. The river Cur appears, therefore, to have been originally the upper part of the Finart, and the Holy Loch to be the representative of the lower pal~ of the first Glen Massa~ The Cur was diverted southwards into Glen Massan at a very remote period by the influence of the strike of the rocks, and has since that date retained the channel which, after long ages of erosion, has been scooped out into the rngged pass now occupied by Loch Eck and the r~ver Eachaig. Glendarud is almost entirely coincident with the strike of the rocks, and it is only at the lower part of the valley that the Ruel appears to have had strength enough to cross their edges. The blue lines on the accompanying map show the probable directions of the original river-courses, and the: red lines the principal watersheds east of Loch Fyne. Let us now take a more general view of the region, and include the large cross valleys in our survey. If the surface of the primeval plateau sloped away from a N.E. axis, how comes it that there are great cross valleys like those of Loch Lomond, Loch Long, and Loch Fyne, which run nearly parallel to the ancient ridge ? Can these valleys be due ,to great fractures or subsidences of the earth's crust, or haw they been worn down by slow degrees like the river-courses ? At first sight the former view seems very plausible. What more natural than to suppose the old sloping platform to have been cut by a series of what in geology are known as "faults," which formed the valleys right off, thus :--

i I ' , iw, i~/ i)' iW l ~latform w= Old Waterpartin~, " o h" WL New D ° Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 Unfortunately for this free-and-easy hypothesis, such faults are con- spicuous by their absence, and the cross valleys must be otherwise accounted for. Let us see if the Denudation hypothesis will help out the solution of the problem. Suppose, for example, a series of rills running down a sloping field, to be cut off at successive distances by transverse ditches, which draw the water aside and prevent it from washing M1 the soil down to the "foot-rig." Each rill drains the area between the ditches at its upper and lower end, and pours the whole of its contents into the latter channel. The erosion at the top would, on account of the small volume of water, be insignificant, and a small ridge would be left TttE DUIvIBARTONSttIRE HIGHLANDS. 345

remaining immediately below the upper ditch, but the ever-increasing size of the stream would give it an ever-growing capacity for deepening its bed towards the lower extremity. In the course of time the main ditches would grow much larger than they were at first, and the soil immediately above them and between the tributaries would be largely washed away, but the position of the water-partings close to the one ditch, and far from the next below, would remain practically unaltered. The denudation of western Scotland seems to have been conducted on analogous principles. The original water-parting was not the top of the Loch Lomond ridge, but a tract of ground in the neighbourhood of what is now Loch Fyne. ]3efore Loch Lomond and Loch Long came into existence, all the country east of Inveraray, and northwards to the Arrochar Highlands and Glen Falloch, was probably drained by the Forth, and not, as at present, by the Clyde. Whether the Clyde itself originally joined the valley of the Forth or not, does not concern the present paper ; but there can be little doubt that the ancient Forth was u much larger river ~han its puny descendant. If the Forth ever drained all the country east of Loeh Fyne, it.must have clone so at a remote part of the Tertiary period, when the present features of the land were but faintly outlined. The Loeb Lomond valley corresponds to the lowest ditch in our field. It appears to have cut off the head-waters of this part of the ancient Forth, and to have drawn them off to the south. Whether the river occupying the valley wheeled round to the east and joined the Forth lower down, or whether it discharged into the Clyde, we shall not stop to inquire, although the subject is very fascinating. When the upper tributaries of the Forth, which must, if my hypothesis be correct, have crossed the country when it was as high as the shoulders of Ben Lomond when these streams were interrupted and drawn off to the south, no waters of any considerable size would be left to cut trenches through the Ben L0mond ridge. Any subsequent erosion which it has under- gone has been effected not so much by rivers as by the general disinte- grating action of the atmosphere, supplemented to a slight extent by the glaciers of the Ice Age. Ben Lomond may be the site 0f a high part of the primeval plateau, but it is equally, if not more probable that the plateau was higher than the present top of the mountain, and that this Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 isolated peak is merely an outlying pillar marking the extent of the erosion of the surrounding country like a column of soil left by navvies in a cutting to mark the depth of their excavation. Although very conspicuous from its isolated position, it must not be forgotten that Ben Lomond is not more than seven miles from the Arroehar Highlands --a tract of country whose average elevation is over 3000 feet--and it requires no great stretch of imagination to suppose them all to have formed a continuous area of high ground before the valley of Loch Lomond came into existence. If the east and west valleys be the oldest, we should expect, at some places at least, to find vestiges of the same ancient channels on opposite 346 THE DUMBARTONSHIRE HIGHLANDS.

sides of the valleys which cut through them. In the valleys of the Inver- uglas and Arklet Rivers, which enter Loeb Lomond at opposite sides, and in exactly the same straight line, we have, perhaps, a case in point. Were the part of Loeh Lomond above Inversnaid to be dammed back by a barrier 500 feet high, the waters from Loch Sloy, Glen Falloch, and the mount~ns to the north would flow off by way of Glen Arklet and Loch Katrine into the Forth, as they probably did long ago. The old Loch Lomond river, which originally drained all the country between Loch Fyne and the Ben Lomond water-parting, was in turn impoverished by having its feeders firm the west cut off when the valley of Loch Long which may be compared to the second ditch in the field-- came into existence. There is here even clearer evidence of the rivers having been deflected and drawn off to the south after they had hollowed out well-marked and normally directed valleys. The low isthmus, be- tween Tarbet and Arrochar, I suppose to be the end of the ancient Glen Croe, before that gorge was cut off and its stream diverted into the Loeh Long valley. There seems to be no other way of accounting for the isthmus, as it lies right across the path of the glaciers during the Ice Age, and could not consequently have been eroded by them, and at present there are no streams of any size, nor is there any gathering ground to support streams large enough to effect its erosion. The Coilessan Glen, a valley between 1 and 2 miles long, which enters Loch Long about 2 miles south of Glen Croe, is exactly in line with Glen Douglas, and may represent its old westward prolongation. It is very difficult to see how, under the present physical condition of the country, the Gareloch could have originated. But if we regard Loch Long as a comparatively recent scar on the face of the country, all is plain. The Gareloch is, I believe, nothing less than the lower part of the old valley of Loch Goil, and was cut off at a time when the river-course was at/east 300 feet above the present sea-level, as this is the height of the ridge between the upper end of the Gareloch and Portincaple on Loch Long. Since the waters of the Loch Goil valley were diverted to the S.S.W., there has been much erosion, and the upper part of the depression has been scooped out to a depth of some hundreds of feet, partly by the river and partly by the glaciers of later times. The lower end of the river- Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 course--the Gareloch~has remained comparatively stationary, as there was almost no eroding power in the diminished volume of water it now carried off. The present depth of the Gareloch at certain places is apparently due to the action of glaciers, which Converted it, like the neighbouring valleys, into rock basins, deeper at the upper than at the lower extren~ty. How Loch Long originated it is difficult to say in lack of sufficient geo- logical and other data. There is clear evidence that it was at one or more periods filled by a huge glacier which reached up to the tops of the hills on either side, and overspread all the low country, as the Greenland and Antarctic ice-sheets do at the present time. The eroding power of ice is very great when forced to flow in a constricted valley for a long period. THE DUY'~BARTONSHIRE HIGHLANDS. 347

Loch Lomond, although quite shallow at the lower end, has been scooped out, at a point above Tarbet, to a depth of over 100 fathoms by the action of ice alone. In some of the Norwegian fiords the glaciers now seen creeping languidly down the upper' reaches were once large enough to overflow the valleys completely, and to hollow out and erode them to depths of 2000, 3000, or even, in the case of the great Sogne Fiord, of 4000 feet ! It is certain that the pattern of the present river system was stamped on the face of the country before the last Glacial Period, as there has not been enough erosion since that date to produce more than a very small quantity of alluvium in the valleys. The glaciers did not then do more than deepen and enlarge existing valleys. Evidence is, however, not wanting of the existence of Ice Ages at earlier parts of the Tertiary Period ; and to the action of the very ancient glaciers, the more obscure physical phenomena of the district may sometimes be due. The probable directions of the original river-courses of Cowail and the district to the east of Loch Long are indicated in blue lines on the accompanying map. The principal water-partings are, for the sake of perspicuity, represented in dotted red lines, the original water-par~ing being shown with a solid line, thus distinguishing it from those of more recent date.

PHYSICAL EXPLOITATION OF THE . BY HUGE !gOBEa~ MILL, D.Sc., ]~\R.S.E., F.C.S., Chemist to the Scottish Ma~e Station. IN a Paper which was published in the January number of the Magazine, I summarised the chief peculiarities of the firths and estuaries on the east coast of Scotland. The subject was necessarily treated in a pre- liminary manner, for few data are to be found recorded, and the accumu- lation of facts by direct observation is never very rapid. The general similarity of the more or less funnel-shaped and shallow sea-inlets of the east coast enables one to generalise safely from the few observations which have been made on most of them, and the pretty complete exami-

Downloaded by [Carnegie Mellon University] at 09:52 18 January 2015 nation of one ; but it is obvious that this generalisation cannot be ex- tended to the sea-loehs of the west of Scotland. Mr. Murray's recent address to the Philosophical Society of Glasgow (a report of which appears in this number) shows that a remarkable difference exists between the physical and biological conditions of the eastern Atlantic, where the watei is deep and comparatively warm, and those of the cold and shallow North Sea. The Firth of Clyde, using the term in its widest sense, as applying to the whole connected system between Glasgow and Ailsa Craig, includ- ing all the loehs and channels, also differs completely in its physical characters from the firths of the east coast. The Firth of Clyde may be regarded as a river merging into an