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Scottish Geographical Magazine Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rsgj19 A bathymetrical survey of the chief lochs and their relation to the glaciation of that district James S. Grant Wilson a a H.M. Geological Survey Published online: 30 Jan 2008.

To cite this article: James S. Grant Wilson (1888) A bathymetrical survey of the chief Perthshire lochs and their relation to the glaciation of that district, Scottish Geographical Magazine, 4:5, 251-258, DOI: 10.1080/14702548808554471 To link to this article: http://dx.doi.org/10.1080/14702548808554471

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TABLE V.--ASCENSION TO CONAKR¥ (Serial Temperatures).

3 ° :'4N. 3 7 ° I"0N 3 ° 2'-3 N.I [4' *' 15 ° 0"9W.[15 ° 54"0W 15 ° 2"1 I

Depth: )6~ 1892 2611 I" 2584

11 March. 112 March. 13 March. / 2 Jany,

~ahr. ° Fahr. o Fahr. ° Fahr. ° Fahr. ° Fahr. 0 1 ') 81 "6 81 "5 80 "8 82"3 82"9 10 0"2 81 '0 81'2 79"2 I 79"8 80 "0 82"0 15 ... 76 "1 81 '0 78"8 I ... 18 76'3 i 7g':v 20 0"2 7"3"7 8i"0 ... i 8b"o 8i':9 20 78 "4 23 7i'.'2 [ ... ,.. ..o 25 76 "2 6g:9 30 9 0 67".9 61.8 ' 6~':8 6~.o 64"8 30 ...... o,. 67"8 32 7io 40 50 •o 5~:9 5""37- ::: 5~':2 5~'.b 57 '8 5~:2 75 7 "9, 56"46 56 "2 ... 56 "7 56 "9 56 "2 100 2 "0 54 "92 55 -8 ... 55 '8 56'0 55 "8 5~:4 150 ... 52 '7 ... 50 '9 51 "2 51 '9 200 ... 5~':83 49.2 ... 47 "2 46 '9 48'0 55":0 300 ... 48 "64 42 '63 43"8( 44 '2 400 ... 42 "21 40 "95 ::: .... 40"6~ 50O 4~:9 6O0 ::: a;':41 89"7( 80O ... 39 '30 39'5~ 1000 38"3~ 8~:1 1250 37 '6~ 37-92 1500 ... o.. 36"9~ 36'98 2000 36 '5~ 2111 2397 ::: 3.~':62 2498 8g':57 ..° 2611 ...... 2725 36'1~

A BATHYMETRICAL SURVEY OF THE CHIEF PERTHSHIRE Downloaded by [University of Ulster Library] at 02:09 12 January 2015 LOCHS AND THEIR RELATION TO THE GLACIATION OF THAT DISTRICT.

:BY JAMES S. GRANT WILSON, H.M. GEOLOGICAL SURVEY.

(Read before the Royal Society, Edinburgh, Feb. 20, 1888. Communicated by permission of the Director-General.) SITUATED within the Highlands of Perthshire are numerous fresh-water lochs, each surrounded with its own peculiar type of scenery. Not- withstanding this diversity, there are certain broad features which are common to them all, ,~nd suggest that the same agencies have been at work 252 BATHYMETRICAL SURVEY OF THE CHIEF PERTHSHIRE LOCI:IS

in each case. During the progress of the Geological Survey in this part of the country four of these have been sounded, and the results obtained show the close connection that exists between the configuration of the various rock basins, and the glaciation of the district in which they are situated. The general trend of the chief Perthshire valley is from west to east, and these are in turn intersected by the transverse valley running south-east from the head of the Garry to . The belongs to both these systems; the upper portion flowing in an easterly direction from the head of Glen Dochart to , thence along the transverse valley in a south-east direction by Dunkeld to Perth. At Ballinluig the Tay receives the outflow from Loehs Rannoch and Tummel, while the surplus water of Loch Earn passes through Strath Earn, and joins the estuary a little to the west of Newburgh. In surveying these various loehs the system adopted was to take a series of soundings (50-80 yards apart) along parallel lines from one side of the lake to the other. These parallel lines were fixed at intervals of about a quarter of a mile, and the observations were checked by other soundings taken in lines extending diagonally across several of the former. A steam launch was employed on , while for the other lakes an ordinary rowing boat proved sufficient.

LOCH RANNOCH.--This sheet of water, 9~ miles in length and having a mean breath of ~ of a mile, lies to the east of the Moor of Rannoch and at an elevation of 667"5 feet. This moor is a wild expanse of peat-moss and heather, and over its surface are scattered numerous small lakes and lochans which all drain into Loeh Rannoch. From the east shore of the loch the bottom descends very steeply, and at one point midway between Altruigh and Curie the greatest depth of 70 fathoms was obtained. Here the loch is a mile broad, and the depth of 70 fathoms is 16 of a mile from the east end--giving an average grade for the central plane of 1 in 22. From the deepest point to where the 10-fathom contour-line crosses the loch opposite Killiehonan, the central plane rises with tolerable re- gularity to the west with an average grade of 1 in 88. Between the 50 and 60 fathoms contour-lines the grade is 1 in 30, but this rise only continues for a short distance. At Carie, Aulieh, Killiehonan, and Crosseraig four large burns flow into the ]och, and the stony detritus borne down by these has in each case formed a large cone of alluvium that projects for a considerable distance into the lake. As might be

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 expected, the depth of the lake suddenly increases along the face of these cones, each resembling the tip end of a railway bank. Several measure- ments showed their angle of slope to be considerably in excess of 20 ° . ]n the deep water only two small banks have been discovered : one lies opposite the mouth of Dull burn, near to the north side and 29 fathoms from the surface, while the other is situated in the middle of the loch, to the north of Crosseraig, in 16½ fathoms of water. The general transverse section of this loeh is in the form of a V, the bottom sloping down from the one side till the maximum depth is reached, and then immediately rising towards the opposite shore. The only exception to this is the small area to the south-west of the Killichonan burn, where the bottom AND THEIR RELATION TO THE GLACIATION OF THAT DISTRICT. 253

is very flat--but this may in part be due to the silting up now in progress at this end. To the south of the Tower Island the water is very shallow, the main channel passing to the north of the island with an average depth of 8 fathoms. Between the mouth of the Erieht and Rannoeh Lodge there is a small depression to the extent of 13½ fathoms at its deepest point. From Kinloch-Rannoch to Aulich the north side of the basin shows a steep gradient towards the centre, becoming less steep to the west of Aulieh. The same steep gradient also prevails along the south shore as far as Dall, but between Altruigh and Carie a belt of shallow water, about 150 yards in breadth, lies between this sharp descent and the margin of the lake. In almost every case where the sounding-line brought up a sample of the bottom, it was found to consist of a very fine brown vegetable mud through which were scattered small particles of white mica. In the shallow water to the east and west of Killichonan this mud was often of a rusty brown colour, due to the presence of a small quantity of iron, and from the Tower Island to the mouth of the river Ericht the bottom was almost entirely composed of fine sand. The west end of this loch is slowly silting up by the deposition of sediment. But this is necessarily a very slow process. The two main feeders at this end, the Ericht and the Ghaoir, respectively drain Lochs Ericht and Laidon a few miles distant. Owing to the precipitation of sediment in these lakes, the amount of suspended matter carried into Loch Rannoch by the Ericht and Ghaoir is small in proportion to their volume. One of the most important features connected with the glaciation of Perthshire is the remarkable fact that during the period of extreme cold, the ice-shed did not coincide with the watershed of this part of the country. During the maximum glaciation, the ice-parting lay between Kinloeh-Rannoch and Tummel Bridge, about 20 miles to the east of the existing watershed. Bearing this in mind, we can satisfactorily account for the phenomenon that the deepest part of Loch Rannoch should be found at its eastern end. The ice, as it passed along the strath of Ran- noeh from east to west, would naturally exert the greatest eroding power at the point where the glacier began to move outwards from the centre of dispersion. Hence we find the greatest depth at the eastern end, which gradually diminishes from this point to the western extremity. The loch thus presents the simplest form of a rock basin due to ice erosion.

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 Stri~e indicating this ice-movement have been found on the hillsides to the south-east and north-east of the loeb, along with others belonging to the later valley glaciation. After passing along Loch Rannoch, this great body of ice, reinforced by the ice from the Loch Ericht basin, would stream over the low ground that forms the Moor of Rannoeh, and find its way to the west by Glen Leven, Glen Etive, and Glen Orehy. Between Claeh-ghlas and Tigh-moir, the eastern margin of the loeh is composed of banks of shingle. For a mile to the east of this, a flat gravel moor forms the valley bottom. Between Tomelachaeh and Dal- ehosnie rock rises above this alluvial haugh, and, stretching more than halfway across the valley, appears to mark the position of the original lip 254 BATHYMETRICAL SURVEY OF THE CHIEF PERTHSHIRE LOCHS

of the rock basin of Loch Rannoch. If this supposition be correct, the ice formed a rock basin, with an average downward inclination of 1 in 34 for 2~ miles, and rising again to the west for 7½ miles, with a gradient of 1 in 88. A few gravel-pits have been opened on this flat to the east of Tigh-moir, and an examination of their contents shows that the stony material is largely moranic in its character. The accumulation of so large a quantity of moranic d~bris at this part of the valley is doubtless due to the fact that it formed one of the terminal moraines of the later glaciers. As the waves on the surface of this lake are constantly break- ing along its eastern margin, they have converted the moranic detritus at this point into shingle, which has been thrown up into a series of small storm beaches. That the river Tummel did not always leave the loch by its present course, is proved by the existence of a well-marked channel along the south margin of the vMley. The river, thus moving from side to side, would remove the irregular mounds scattered over the surface of this terminal moraine, and leave the broad flat moor that now lies between Kinloch and DMchosnie. The small depression already mentioned, that lies between the mouth of the river Ericht and Rannoch Lodge, is doubtless due to the junction of the Ericht and Rannoch ice at this point. With the exception of a small area of granite at the west end, the rock basin of Loeh Rannoch has been entirely eroded out of micaceous quartz-schist, with bands of quartzite and mica-schist. Through these are intruded sills of quartz-porphyry and altered basic rocks; and as the general dip of the beds is to east, the denudation of this rock basin has been at a right angle to their strike.

LocH TU~IMEL.--This lake lies 9½ miles to the east of Loch l~an- noch, with which it is connected by the river Tummel. The surface of the lake is 453'5 feet above sea-level, or 214 feet lower than Loch Ran- noch. Although the total length of this loch is only 22 miles, its physical structure is very interesting, as it contains three distinct basins. The deepest basin is found at the west end of the loch. Its maxi- mum depth is 20~ fathoms, and the area embraced by the 20-fathom line is situated at the upper end of the basin. This basin is separated from the middle one by a sill of rock covered with 8½ fathoms of water -~t its deepest point. This sill coincides with a large fault, with down- throw to east. The beds on the west side of this fault are the soft grey

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 mica-schists that overlie the crystalline limestones of Glen Tilt and Loeh Tay; while on the east side of the fault, the hard upper quartzite beds occur that form the south side of Strath Tummel. The middle basin has been excavated entirely out of these hard quartzites, and its greatest depth of 19½ fathoms is also found at the upper end of the basin. The lower basin is divided from the middle one by a similar rock sill in 9 fathoms of water. This basin is the smallest of the three, and has a central depth of 16½ fathoms. Taking these facts into consideration, it is clear that they are quite in accordance with the belief that Loch Tummel is a rock basin, exca- vated by ice. On the hill slopes on either side of the loch abundant AND THEIR RELATION TO THE GLACIATION OF THAT DISTRICT. 255

strim are met with, showing that the direction of the ice-movement was E. 15 ° to 30 ° S. We would naturally expect, therefore, to find proofs of greatest erosion at the western ends of the rock basins. A glance at the chart will show how the contours of the several basins in Loeh Tummel illustrate this phenomenon, and how the two upper ones, each about a mile in length, gradually diminish in depth towards the east. Another point of interest presented by this loeh is the fact that the relative hardness of the rock out of which these basins have been excavated seems to have made no difference to the grinding power of the glacier. As mentioned above, the upper basin lies entirely in soft grey mica-schist, while the two lower ones have been scooped out of hard quartzite rock.

Locg TAY.--This sheet of water, the largest of the Perthshire lakes, is 14½ miles in length, with an average breadth of about ~ of a mile. Calculated from the bench mark on Kenmore Bridge, the mean surface level of its water is found to be 34:6 feet. In outline it is very similar to the letter S. The lower portion of the letter is represented by the part from to , and extends E. 25 ° N. From Ardeonaig to Fernan the axis of the lake lies N. 30 ° E., and from the latter point to Kenmore it resumes its original direction of E. 25 ° N. At the west end it is fed by two considerable rivers--the Dochart and Lochay; and from Killin to Kenmore it drains the hill basin in which it lies by means of numerous small streams. The largest of these are the , Ardeonaig, Morenish, and burns. The rivers Loehay and Dochart join a short distance below the village of Killin, and from the point where their combined waters enter the loch to the steamer pier the western margin of the loch is very shallow. About ~ of a square mile of marshy ground lie between Killin and Loch Tay, and this has been formed by tim detritus brought down and deposited by these two rivers. That this alluvial flat has a considerable depth is shown by the fact that a bore of 12 fathoms, put down where the railway bridge spans the Lochay, failed to find a rock bottom. The silt- ing up of the loch at its west end is proceeding rapidly. Since 1861, when the ground was surveyed by the Ordnance Survey, the spit on the north side of the mouth of the conjoined rivers has advanced ½ of a mile further into the loeb, while a considerable portion of it has been raised by- drifted sand above the surface of the water, and is now covered with

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 scrub and grass. At the extremity of this spit the river water, in joining the loch, has formed a bar, and beyond it the depth of water increases very rapidly. To the east of Firbush Point very shallow water lies along the shore, with a sand spit that extends about 200 yards into the loeh, and in the direction of the river bar. When the Ioch is standing at its summer level, the sandy shore around its western margin is often covered with patches of bright red sand. This red sand forms a thin layer on the surface of the ordinary yellow siliceous sand that lines the shores. On examination it is found to be almost entirely composed of minute fragments of garnets, and these particles, on account of their lighter specific gravity, have been sifted out 0~56 B.4.THYMETRICAL SURVEY OF THE CHIE]~" PERTHStIIRE LOCHS

by the moving water from the denser siliceous materials, and deposited on the top of them. To the south of the steamer pier the loch is very shallow for about a of a mile from the shore, but beyond this the depth rapidly increases till 24 fathoms is reached. From this point eastwards the bottom of the loch slopes gently downwards, till, at a distance of 3½ miles from Killin, it is covered with 50 fathoms of water. This gives an average grade for the central plane of 1 in 61. A transverse section across the basin opposite Creagard shows that the sides slope evenly downwards to the maximum depth, the declivity of the south slope being twice as great as that on the north side. From Creagard to Ardeonaig the lake becomes slightly shallower, and has an average depth of 46 fathoms of water. From Ardeonaig to Skiag the central plane again descends with con- siderable regularity to the east, with an average grade of 1 in 100. To the south of Balnahanaid the bottom of the loch is situated below sea- level, and continues so for a distance of six miles to the north-east. From Tullochcan to Ardtalnaig numerous transverse sections have been plotted across the basin. These all show that the sides slope regularly down till the maximum depth at any one point is reached, and that the bottom there for about ~ of the distance across is almost level. Below Skiag is situated the deepest portion of Loch Tay, covered with 85 fathoms of water, and at this point the bottom is 166 feet below sea-level. Here the loch is only 1110 yards wide, and this is the nar- rowest part between Ardeonaig and Acharn. A transverse section of the loch between Skiag and Cragganruar shows that both sides slope steeply downwards to the maximum depth. Between Skiag and Kenmore the central plane rises with tolerable regularity to the east, with an average grade of 1 in 57. Several sections have been plotted across the lake between these two points, which show that the bottom is rather irregular, and that the south side of the basin is much steeper than the north. The chief burns that flow into the loch at Acharn, Ardtalnaig, Lawers, Ardeonaig, and Morenish formed large cones of detritus that project for some distance into the lake. The face of these is very steep, and deep water is found close inshore. All over the loch the sounding-line brought up samples of the bottom, and this almost invariably consisted of very fine mud, composed of impalpable fragments of peat and vegetable debris, mixed with small scales of mica. In the bay at Fernan, and between Acharn and Kenmore, stiff yellow clay formed the bottom,

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 while the west end is chiefly occupied with fine sand. At the time when the great ~er de glace covered the whole of Scot-. land, it moved over this part of the country in a south-easterly direction. Numerous grooves and strim have been found on the hill slopes and summits on both sides of the loch, and these show the direction of the movement to have been E. 20 ° to 30 ° S. Between Ardtalnaig and Auch- reich the ground rises rapidly from the edge of the loch to 2360 feet, and the shoulder of that faces it on the north side is corre- spondingly steep. (See section on cha~'t.) The slope to the north of Ardtalnaig is almost destitute of any covering of drift, and the quartz- porphyry, that forms the rock in situ, exhibits marks of intense glacial AND THEIR RELATION TO THE GLACIATION OF THAT DISTRICT. 257

action and has been grooved, striated, and polished in many places. The direction of these strim range from N. 30 ° to 35 ° E., and the appearance of the strim shows that the ice passed from south to north, although some of these may belong to later valley glaciation. I am inclined to believe, from a consideration of the whole evidence, that they were formed by an under- tow of the great ice-sheet. Where the steep slope at Ardtalnaig prevented the direct passage of the ice, the under current, deflected for a short distance to the north-east, must have had a powerful erosive effect along the base of the slope. The pressure would be intensified by the confined nature of the valley. Hence the deepest part of the Loch Tay basin would naturally be formed where we now find it, between Ardeonaig and Fernan. Owing to this undertow the bottom layers of ice would travel eastwards towards Kenmore till the decrease in the height of the hills to the south allowed of their passing over them. The direction of this movement would then coincide with that of the main mass, viz., E. 20 ° S. It is important to note that between Ardeonaig and Fernan a large fault occurs with a downthrow to the west. The points at which it enters the loch at both these places have been accurately fixed, and its probable position along the bottom has been indicated on the chart. The fault in the first instance may have determined the direction of the loch between these two points, but in my opinion it does not explain why the deepest portion of the basin is situated at Skiag. Had Loch Tay been an ordi- nary type of rock basin the greatest depth would been found somewhere to the west of Ardeonaig, but the soundings, viewed in connection with the other glacial phenomena, show that it is a very good type of a deflection basin.

LOCH EARN.--This loch lies 6 miles due south of the Killin end of Loch Tay. It is 6½ miles in length, and is situated at an elevation of 306 feet above sea-level. It receives the drainage of the surrounding country by means of numerous small streams, while the surplus water is discharged into the river Earn, which flows out at the east end. Inshore around Lochearnhead the upper end is shallow, but beyond this the depth steadily increases till the deepest sounding of 48 fathoms is reached to the north of Ardvor]ich. This gives an average grade for the central plane of 1 in 46. A transverse section of the lake at this point shows a flat-bottomed trough, with a sharp declivity on the south side. From Ardvorlich to St. Fillans the central plane rises with great re-

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 gularity with an average grade of 1 in 74. Transverse sections of this portion of the loch show that it has a velT flat bottom, and the south slope of this rock basin is twice as steep as that on the north side. Everywhere the basin is covered with a brownish-black vegetable mud, similar to that found in the three lochs already described. Loch Earn thus presents the simplest form of rock basin, and as the great mer de glace passed over this portion of the country in an ESE. direction it naturally exercised the greatest pressure along the south side of the valley, and this is the reason why the southern side of this rock basin is twice as steep as its northern slope. The same fault that runs through a portion ofLoch Tay intersects the upper part of Loch Earn, 258 GEOGRAPHICAL AND HISTORICAL SKETCH

but it does not seem to have exercised any influence upon the direction or configuration of this basin. Cones of detritus have been formed by all the large burns that flow into this loch with deep water close inshore. This loch was partially sounded by Mr. Sandison of St. Fillans, and the record of these I have used, supplemented by those soundings taken by myself.

A SHORT GEOGRAPHICAL AND HISTORICAL SKETCH OF BOSNIA AND THE HERZEGOVINA.

BY E. B. FREEMAN, H.B.M. CONSUL, BOSNA-SERAI.

THE whole of Bosnia and the Herzegovina belongs to the "Karst" district, which may be said to extend from the Kraina to the southernmost point of Greece. What is understood by "Karst" is a rocky formation with only a slight depth of soil, wooded in some parts, but where the forests have been destroyed, and the soil consequently washed away, presenting a barren, inhospitable, undulating, rocky surface. Everywhere in Bosnia are to be seen the deeply-indented mountain- sides of chalk or limestone, lying chiefly on a substratum of clay-slate, peculiar to the Karst formation, and the deep-cut valleys and river-beds between wall-like rocks not unfrequently 1000 to 1200 feet high ; like- wise tile caves and caverns so common in this formation, where often whole rivers disappear in the bowels of the earth, in some cases to reappear again many miles distant. In some parts of the country periodical lakes are formed by these rivers, owing to an insufficient out- let for the water through the caverns during the rainy season. The rivers Bosna, Vrbas, Sanna, and Unna all gush out from the earth as large streams. The valleys often widen out into plains of considerable extent, offering a fertile field of alluvial soil to the agriculturist. The river system is much cut up and divided by plateaux having an altitude sometimes in Bosnia of 3000 feet. In the district of Nova- Bazar, which, though no longer politically, is yet ethnographically, part of Bosnia, there are plateaux of even 6000 feet, and the Dolomitic mass of the Dormitor in Montenegro, close to the south-eastern frontier of the

Downloaded by [University of Ulster Library] at 02:09 12 January 2015 Herzegovina, attains an extreme height of 7200 feet. Although all the natural phenomena of the " Karst" formation are present in Bosnia and the Herzegovina, it must not be supposed that the country resembles the barren "Karst" of Istria. The greater part of the Bosnian mountains are covered with magnificent forest, for "Karst" is seldom bare rock by nature. It is the hand of man which renders it so. The forests are recklessly cut down so as to cultivate the shallow soil, or to feed the goats on the leaves of the trees towards the end of summer when other food fails, or it may be for the sake of the timber, and in a few years the scanty soil is washed away by the rain, and nothing remains but barren rock.