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THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 25

IX.—The Glacial Geology of the Stonehaven District. By ALEX. BREMNER, M.A., D.Sc, F.R.S.E.

(Read 17th January, 1917.)

THIS paper is a contribution towards the solution of one of the problems in the glacial geology of north-east Scotland, mentioned in a paper published in our Transactions (vol. x. p. 334), viz., the relations in space and time of the ice that distributed the red clays from Strathmore along the coasts of Kincardineshire and Aberdeenshire with that which brought the Upper Grey Boulder Clay. The latter we shall speak of in this paper as the Dee Valley Ice : the former we may call as before the Strath­ more Ice. In addition the paper may be interesting per se as a contribu­ tion to the study of the surface geology of a district to the solid geology of part of which special attention has been called in recent years. The area dealt with is bounded by the sea and a line drawn due west from Portlethen village to the Dee watershed, following the Dee watershed to the gap between Monluth and South Dennetys and passing thence southward to the Bervie Water at Milton of Dillivaird, along the Bervie to Drumlithie, and from that point straight back to the coast at Dunnottar Castle. The localities mentioned will be found on Sheets 66 and 67 of the 1-inch map.

A. DIRECTION OF ICE MOVEMENT. It is natural to infer that in this district the latest glacial phenomena would be due to an ice movement from the high ground to the low ground. This was the inference drawn by Dr Jamieson 1 when he described the Kaims2 of Candy as the terminal moraine of the Bervie Water glacier. There is at present only one good open section in these kames and this shows true kame structure. On their eastern side the kame deposits are overlaid by boulder clay : this is interesting as showing their sub-glacial origin. Further, the most prominent erratics present are fragments of Strathmore shales which must have come from the south or south-west: of granite boulders there are none or very few. Along the Bervie Water between Candy and the boundary fault there is also a singular scarcity

1 Quart Jour. Oeol. Soc, vol. xxx. (1874), p. 326. J So spelt on O.S. 6-inch map. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

26 EDINBURGH GEOLOGICAL SOCIETY. of granite boulders. Such as do occur are well-rounded and probably come from some of Dr Campbell's " Highland Con­ glomerates " in the Old Red Sandstone area.1 These facts are sufficient to prove :— (1) That the Kaims of Candy are not moraines but sub-glacial deposits. (2) That in late glacial times no glacier descended the valley of the Bervie, the most considerable valley in the district, and that carrying off the drainage of the highest ground. Since this valley heads well back within the newer granite area, erratics of that rock should have been abundant along the track and in the terminal moraine of its glacier. What has been said of the Bervie valley is true of the whole district—that there is no carry-over of erratics from the higher ground north-west of the boundary fault on to the lower ground to the south-east of the fault. Everywhere within the Old Red Sandstone area the occasional granite boulders are generally well rounded and in all probability derived from the conglomer­ ates. It must be kept in mind, however, that the North Esk glacier, an important affluent of the Strathmore Ice, may have brought from the Mount Keen district a certain proportion of boulders of newer granite. On the sketch map are recorded all the striae due to the Strath* more Ice and a selection of those due to the Dee Valley Ice that occur within or near the borders of the district under review. The paucity of the former is doubtless to be attributed to obliteration by the later ice and to the ravages of marginal drainage; for it has been my experience that, in the vicinity of marginal channels, stria? are seldom found though the exposed rocks may show evident traces of ice-moulding. Two striae are inserted north of the Dee in order to indicate the direction of the main stream of the Dee Valley Ice : others prove as clearly as possible the fanning out of that ice as it neared its termination. The striae afford conclusive proof that, during this latest phase of the ice-sheet, the ice from the Dee valley and that from Strathmore did not, as depicted in most glaciation maps, unite somewhere between Stonehaven and Aberdeen and then flow north-north-eastward as a single stream.2 Whether the phenomena dealt with in this paper belong to a distinct Glacial Stage is not—and perhaps may never be—clear. But it is at least perfectly evident that the movements recorded by the striae cannot have been contemporaneous.

1 Trans. Roy. Soc. Edin., vol. xlviii. (1913), p. 941. 8 They may have done so—and probably did do so—during an earlier phase of the Ice Age (vid. lot. cit. sup., p. 336). Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 27

f ' / f A (Strathmore Shales Scale oi mlUs'

-Old Red Sand stone Crawton Basalts) I Crawton Basalts Downton/an Glacial ,Striae Boundary of Newer Granite Mass

K <' G.reat Boundary fault ^. ^ Seaward Li mit of De e Val ley Drift Boundary between the two varieties of Dee \aJ ley Drift Lines of movement of the Strathmore Ice as

he lines radiating,from n?8r Tewej shew the disper­ sion of the mottled Downtonian Sandstone. Fig. 1. Glaeiation map of the Stonehaven District, Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

28 EDINBURGH GEOLOGICAL SOCIETY.

Three instances of cross-striation occur, and in all three the later striae are those impressed by the Dee Valley Ice. For example, a mile north of Muchalls Station and a quarter of a mile east of Nether Cairnhill a large roche moutonnee has been moulded—and plucked—by ice from S.S.W., and shows one small striated patch with striae pointing N. 27^° E. : it is also well striated from between N.W. and W., the direction of the striae varying from E. 27|° S. to E. 35|° S. This is in harmony with the evidence afforded by the stratigrahpical relations of the boulder clays left by the two ice-lobes. That evidence has already been given in some detail (Trans. Edin. Geol. Soc, vol. x., Part III, pp. 334-8, 345-7), and in this paper will be mentioned only incidentally. At some future time I propose to give a full list of all the striae observed in the basin of the Dee and adjoining districts. Mean­ while it may be mentioned (1) that within the area covered by the sketch map my list includes 78 besides numerous unstriated roches moutonnees; (2) that of the meagre array of arrows on Sheets 76, 77, 66, 67 of the Geological Survey map few are to be relied on—some are as much as 60° wrong. The direction of the arrow shown in-the sketch map, on the north side of Cairnshee, may be compared with that of the one at the same point on Sheet 66.1 The direction of the ice-movements is also perfectly clear from a study of the distribution of erratics, if we fix our attention on a few of the most typical and readily identifiable of these. The rock types, occurring as erratics, which may be used as indices are:— 1. Strathmore Shales ; 2. A curiously mottled (" pock-marked ") Downtonian sand­ stone, seen in situ in an old quarry near Tewel Schoolhouse ; 3. Stained quartzite pebbles from the Old Red conglomerates ; 4. Crawton Basalts ; 5. Newer granite (mainly flesh coloured); 6. Older granite (pale pink granite, pegmatites); 7. Gnarled gneisses, such as occur on the Dee watershed east of Cairn-mon-earn. The tracing of these erratics enables one to set down on the map the limits of the different drifts and direction arrows in­ dicating ice-movement.

1 There seems to be—as one would expect—some evidence for two ice- movements across the high-ground between Cairn-mon-earn and Girdleness— an earlier from west or somewhat south of west and a later indicated by the striae now recorded. To discriminate between the two sets of striae is exceedingly difficult: the form of the ground may cause considerable divergence (some­ times as much as 30°) among striae due to the same movement. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 29

B. DISTRIBUTION OF THE STRATHMORE DRIFT. The ground moraine of the Strathmore Ice, everywhere recognisable by colour and contents, has been carried for nearly forty miles beyond the boundary fault and left in the coastal districts as far north as Peterhead, while in the Ythan valley it extends ten miles inland. Yet very little red boulder clay is found on the hills between the great fault and the Cowie Water. What little there is extends only a short way up the south-eastern flanks of these hills and never, so far as I have seen, reaches the top of the slope that rises sharply from the boundary fault. On the other hand stained quartzite pebbles are distributed somewhat thinly over the whole of this area; and a nest of them, including one which is broken but still weighs over 20 lbs., has been found right on the Dee watershed in the dip between Craigbeg and Mongour, 1000 feet above the sea. On the Hill of Trusta (1051 feet) they are found within a short distance of the summit. On the slopes between the Bervie Water and Brawliemuir none were found ; but there little drift of any kind occurs, and the solid rock is everywhere near or at the surface. In the Stonehaven district the main stream of the Strath­ more Ice seems to have followed a course varying between north­ east and north. This is proved by the distribution of erratics (1) and (2). Its surface rose high above the schist hills over­ looking the Old Red Sandstone area ; and its upper, cleaner portion streamed over the Carron-Cowie watershed, completely enveloping Trusta Hill, and even reached as far as the Dee watershed. This, it seems to me, it could have done only if it met with little or no opposition from the Dee Valley Ice, which we are safe to say could not at that period have surmounted in any force the Kerloch-Cairn-mon-earn ridge. • What was the area originally covered by this quartzite drift one can only conjecture, since the subsequent advance of the Dee Valley Ice has so completely cleared out or covered up all traces of Strathmore drift in places where one is safe to infer that it once was present. Besides, much of the area in which quart­ zite drift might reasonably be looked for consists of grouse moor where the search for erratics that are usually small enough to be hidden by even low heather is somewhat disheartening work. Good drift sections, too, are very scarce. If, however, quartzite drift swathes the whole of Trusta Hill (except where it has been cleared off by the readvance of the Dee Valley Ice) and reappears three miles further north, it must have at one time spread to the hills forming the Dee-Cowie watershed east of Cairn-mon-earn. The ascertained distribution of the Strathmore Drift is shown on the sketch map. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

30 EDINBURGH GEOLOGICAL SOCIETY.

C. DISTRIBUTION OF THE DEE VALLEY DRIFT. The evidence for a readvance of the Dee Valley Ice after the Strathmore Ice had retreated altogether, or at least greatly diminished in volume, is very clear; but the point of greatest theoretical importance that can be established by a study of the glacial deposits of this district is the precise limit reached in the readvance. The drift left by the Dee Valley Ice is characteristic and of two kinds : each kind occupies a well-defined area. (a) West of a line drawn from the eastern margin of the newer granite mass to the Roman Camp at Raedykes the drift consists largely of fragments of newer granite. Over the greater part of the area newer granite forms more than 90 per cent, of the erratics. The ground between the east-west part of the Cowie Water and the granite margin is so thickly covered with granitic debris that the solid geology can be mapped only from stream sections. Granitic erratics form a decreasing but still large proportion of the drift the further they are traced from the Kerloch-Cairn- mon-earn ridge. On the south side of the Cowie Water the boundary of the granite drift is very clear. Opposite the great gap between Monluth and South Dennetys it rises somewhat above the 1000 feet contour, granitic debris becoming scarcer as the upper limit is approached. Along the north and north-east flanks of Craiginour the bound­ ary is an interesting marginal channel which begins slightly below the 1000 feet contour and descends south-east to the 800 feet contour. In some places it is a notch cut in the hillside ; in others it forms a definite rock gorge, e.g., where it indents the 900 feet contour. On the west shoulder of Trusta granite boulders are found up to over 800 feet. Along a line joining the lower end of the Craiginour marginal channel and the shoulder of Trusta an immense quantity of drift, predominantly granitic, has been piled up. South of this line, and at a level of slightly over 800 feet, a glacial lake was held up. Proof of the existence of this iake cannot be found in a definite lake terrace or margin. But the streams that drain the old lake basin are cutting through thick sands and gravels that cloak the slopes up to, but not above, the old water level. The Finglennie Burn pursues a very winding course amongst these old lake deposits, and some good sections are seen in its banks, especially where it cuts through the moraine deposited by the ice that dammed the glacial lake. Along the Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT 31 southern side of the old lake basin granite boulders are scarce and have doubtless been transported by drift ice. When the lake reached its highest level, its surplus waters cut a beautiful overflow channel across the Cowie-Carron water­ shed. This channel will be referred to later (Cold Well Overflow Channel). At a later stage the lake drained along the ice margin, where it rested at a level of about 800 feet against the northern flank of Trusta Hill. At this level we find the intake of a very well- defined marginal channel: the channel descends eastwards and can be traced for about half a mile. At a still later stage the lake seems to have been divided into two by Hill of Laird's Leys,1 a considerable part of which is moraine. One portion occupied the lower part of the valley of the Finglennie Burn : it drained eastward, south of Hill of Laird's Leys by an exquisite little channel, 40 to 50 feet deep and partly cut in rock, into a second lakelet. This in turn drained along the ice margin as in the previous stage : its over­ flow has cut an ill-defined shelf on the side of Trusta. Along the north side of Trusta Hill the drift margin is difficult to trace owing to the wet soil and a growth of peat, bog-plants, and heather; but quartzites are found high up the hill and granite only (with fragments of local rocks) towards its base. Further eastward in the direction of Clochanshiels Farm, the boundary again becomes very definite. At a level of some­ what over 700 feet occurs a small marginal channel: below it granite boulders are freely scattered over the hillside ; above it not one was seen. Somewhat higher up the hill stained quartzites were observed, the interval between the marginal channel and the first occurrence of quartzites being overgrown with rank heather. Along the slopes between Clochanshiels and Burn of Day no feature marks the boundary, but it can be traced by noting the nature of the surface boulders. On the watershed near Burn of D,ay Farm, at an elevation of slightly over 600 feet, are some low, ill-defined gravel moraines ; and a small overflow channel, with peat-covered floor (=Rough Moss), slopes south­ wards towards the Burn of Baulk. From this point by Hill of Swanley and Cheyne Hill surface boulders and small sections enable one to trace the granite drift. On the summits of Swanley and Cheyne Hills foreign material is very sparsely distributed, and the junction between the two drifts cannot be laid down with precision. Granite boulders, some of considerable size, are found on the east face of Cheyne Hill as far south as Cheyne Farm. It is uncertain whether 1 South of Lady's Leys, and 737 feet in height. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

32 EDINBURGH GEOLOGICAL SOCIETY. they were carried over the hill or deposited by the fanning out of the Cowie Glacier, a tongue of the Dee Valley Ice, when it reached the low ground west of Stonehaven. The former supposition seems the more likely since the surface boulders on the fields of Redcloak Farm are derived from Old Red sources. Probably only a thin layer of ice surmounted Cheyne Hill; for around Cheyne Farm many stained quartzites and fragments of the pock-marked Downtonian sandstone are found along with the granite boulders, and red boulder clay is turned up by the plough below the farm steading. The Cowie valley is very windingand along it a glacier would have difficulty in forcing its way. The tongue of the Dee Valley Ice, whose margin we have just traced, seems to have ended in the gap between Cheyne Hill and Raedykes Hill. From its termination a train of overwash was spread out along the Cowie Water and can be traced to the coast.1 At many points in the grounds of Ury House, on both banks of the Cowie, red boulder clay (or red brick clay, or soft, red, loamy sands), resting directly on solid rock, is covered by coarse granitic gravels. That the Cowie ice-tongue remained stationary for a consider­ able period in the gap between Cheyne and Raedykes Hills is rendered evident by a large overflow channel cut on the north­ east side of the former. It begins at a level of slightly over 400 feet and just indents the 200 feet contour. In its course the meltwater formed a considerable waterfall and tumbled over a lip of hard schist into a big pot-hole, the Devil's Kettle. Above the fall, on the hard rock, this channel is 20 to 30 feet deep : further down, on the softer rock, it is more than twice that depth. Unlike the channels on Craiginour and at Clochan­ shiels the channel does not mark the utmost limit reached by the Dee Valley Ice : large unrounded granite boulders are quite plentiful for nearly a mile further east, and are found on the top of Cheyne Hill (532 feet). Beyond this channel, however, the ice seems to have made but a short stay. The ice that brought the granite drift seems to have entered the Cowie valley over the ridge between Kerloch and Cairn-mon- earn and in greatest force through two gaps in that ridge, (1) between South Dennetys and Monluth (Monluth Gap) and (2) between Craigbeg and Cairn-mon-earn (The Slug). Both show signs of intense glacial erosion. The former is a wide, deep, steep-sided trench whose floor is littered with huge moraine: the latter is a typical ice-worn col with moutonnee rocks on floor and sides. At its eastern end there is an abrupt drop as if the ice, forced up from the lower ground in the Dee basin, had 1 This train contributes numerous granite boulders to the storm beach at Stonehaven. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 33 stuck for some time in the jaws of the pass and the meltwater cascading from it had eroded the deep rock gorge at the Stone­ haven end of the Slug : the head of the gorge is closed by a wall of solid rock. Another shallow gorge, evidently cut by melt- water, occurs at a higher level on the west side of the pass. The ice that streamed through the Monluth Gap, reinforced by that which surmounted the ridge to the eastward, seems to have moved down the upper Cowie valley. We have already noted that as one passes down the valley the gra-nite drift is found at lower and lower levels along its southern side. The lower level reached by the granite drift at Clochanshiels com­ pared with that at which it occurs on Craiginour might be ex­ plained as due to the greater distance of Clochanshiels from the granite ridge. But in the drift exposed in section at various points along the Cowie (e.g. near Mergie, at Bridge of Swanley and Bogheadly) fragments of dolerite may be noticed : these have in all probability come either from a dyke a little to the east of the Monluth Gap or from one at the head of the West Dumer Burn. Their distribution points to a down-valley movement of the ice. Near Mergie the ice that came down the upper Cowie valley was reinforced by that which forced its way through the Slug, and the ice tongue formed by their union reach the limit above described. Whether Cairn-mon-earn formed a nunatak in the Dee Valley Ice is uncertain ; but, judging by the limited seaward extension of the ice down the Cowie valley, one is safe to say that the hill could not have been deeply covered. (b) After passing Cairn-mon-earn the Dee Valley Ice was no longer restrained by the elevated granite ridge on its right side and could fan out more freely across the watershed. This fanning out is clearly shown by the ice-worn older granite and gneiss at the eastern end of the newer granite mass. Accordingly to the east of the line joining Cairn-mon-earn and Raedykes Hill one notes a remarkable diminution in the proportion of boulders of newer granite and the presence of many boulders of gnarled gneiss and older granite. From Cairn-mon-earn nearly all the way to the coast at Aberdeen the Dee watershed was completely overridden, and the ice reached the sea along a front of considerable extent. The height of the watershed1 declines pretty gradually from 975 feet at Strathgyle to 200 feet at Tullos Hill. But the ice surface seems to have sunk more rapidly; and, while it was able to cross the watershed for the greater part of the distance between Strathgyle and Aberdeen, the ice for the last three miles—where 1 At Red Moss, five miles north of Stonehaven, it sinks below 400 feet. C Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

34 EDINBURGH GEOLOGICAL SOCIETY. the watershed sinks below 300 feet—was able merely to surmount but not to cross the ridge between the Dee-valley and the sea. Tracing the margin of the Dee Valley Ice beyond the end of the Cowie ice-tongue, we find that it reached the top of the slope 1 north of Ury House but did not descend into the valley of the Cowie. Just behind the mansion house there is a deep section entirely in red clay. The Burn of Monboys, an insig­ nificant stream, has cut a considerable rock gorge between Glithno Farm and Ury House : this was probably the course of a direct overflow of meltwater from the ice-front. In the lee of Raedykes Hill and of White Hill (Glithno) inliers of red clay, with boulders from Strathmore, are found. In the gap" to the west of Hill of Megray the ice seems to have reached the 300 feet level. It probably overtopped Kempstone Hill, but did not spread far down its seaward side ; and did not, between Limpet Mill and Cortins, reach the Aberdeen and Stone­ haven turnpike. What I take to be the ill-defined terminal moraine is to be seen to the north of Auquhorthies Farm. At Muchalls the Dee Valley Ice reached the present coast-line. Near Muchalls Station there are several sections which show a curious jumble of red and grey clays : on the cliff tops near by grey clay overlies red boulder clay, and this rests on rock. To the south of Muchalls the overflow channel of Den of Buck, cut in rock and clearly formed in connection with the Strathmore Ice, remains unfilled and unmodified. Further north a fine section in Upper Grey Boulder Clay2 (with included erratics derived from the red clay) occurs near Newtonhill, just east of the railway viaduct over the Burn of Elsick : on the cliff tops the same boulder clay overlies red clay (with Strathmore erratics), which in turn rests on solid rock. For some distance north of Newtonhill drift sections are scarce and poor ; but at Portlethen village Old Red erratics are so abundant along the cliff-tops that one is pretty safe to infer that at this point the ice-front had emerged from the sea.

D. OVERFLOW CHANNELS. In the region occupied by the Strathmore drift alone, the most interesting glacial phenomena are the overflow channels eroded during the southward retreat of the ice : several overflow channels cut by meltwater from the Dee Valley Ice stand in 1 This slope is covered by old pasture from which all large surface bpulders have been removed for fencing : sections are wanting and the margin of the drift cannot be clearly traced. * Trans. Edin. Qeol. Soc., vol. x. p. 3. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 35 curious and important relation to certain of these and may be considered along with them. 1. White Hill (Glithno) Channel. This channel slopes from south-west to north-east, and its intake is just over 400 feet above O.D. It is rock-walled and peat-floored, but the rocky sides have lost the sharpness char­ acteristic of most overflow channels : they have been subjected to a feeble glaciation by the Dee Valley Ice. 2. Limpet Burn Channel. 3. Cortins Channel. 4. Wester Logie Channel. The Limpet Burn Channel is a characteristic example and for most of its length is cut in rock to a depth of over 50 feet. It now carries off the drainage of the flat moorland on which the White Hill Channel opens : that drainage had, in preglacial times, probably passed southward by the Megray Burn to join the Cowie. While the channel was being eroded, the ice must have stood near the intake at an initial level of at least 350 to 360 feet, else the meltwater could not have flowed across the watershed between Megray and Kempstone Hills. When the ice-level sank below 320 feet, the present level of the watershed1 between the Megray and Limpet Burns, the channel ceased to act. From the east end of the channel a flat—or faint terrace— can be traced northward for a mile and a half; it terminates near Cortins Farm in a small rock gorge which is truncated by the Den of Buck Channel. Contemporaneous with, or more probably a little later than, the Limpet Burn Channel is a-small marginal channel which indents the 300 feet contour at Wester Logie 2 : this, like the preceding, is continued northward for a short distance by a distinct terrace or shelf, cut in the drift-covered slope. Below the last-mentioned channel and terrace there com­ mences at a level of 270 feet to 280 feet a very clear terrace feature ; it slopes northward and can be followed as far as Limpet Burn. These terraces must have been cut by drainage passing north­ ward along the edge of the slowly retreating Strathmore Ice when it occupied the bed of the North Sea and a narrow strip of coast while the higher ground to the west was ice-free. 5. Den of Buck Channel. The intake of this channel is on the top of the sea cliff at a

1 The level of the watershed has, however, been slightly raised by material •deposited by the Dee Valley Ice. * See 6-inch map. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

36 EDINBURGH GEOLOGICAL SOCIETY. level of 170 feet: it slopes northward and terminates 130 feet above O.D. As stated above it truncates the Cortins Channel. 6. Den of Cowie (or Logie) Channel. The intake is 187 feet above the sea, but on both sides its walls rise more than 200 feet above O.D. : at its northern end it breaches the sea-cliffs at a height of over 100 feet. It will be referred to later. For most of its length it is at least 60 feet deep. 7. Aligned Sequence of Channels between Quithel and Bum of Day. There are four very distinct marginal channels (a, b, c and d) forming an aligned sequence across the hill-spurs that rise above the boundary fault. The most westerly, a, crosses the hill above Quithel at a level of slightly over 800 feet; b is a deep gash on the Mid Hill Spur somewhat below that level, the 800 feet contour following the top of its north wall; c forms a conspicuous feature on the spur between the two branches of the Burn of Elfhill; the eastern end of d, on the Elf Hill ridge, indents the 700 feet contour. At slightly lower levels than b and c shelves or terraces have been cut at a later stage by marginal drainage. A fifth member of the series probably cut across the watershed between Burn of Baulk and Burn of Day. This is suggested by a shelf on the hill-slope east of d. But the channel, if it ever existed, has been obliterated by the subsequent encroachment of the Dee Valley Ice; and a small channel, sloping in the reverse direction, has been cut by meltwater from the later ice. Between b and c and between c and d are deposits of gravel, that between c and d forming quite a conspicuous flat. Between a and 6 only fragments of a similar deposit remain : it has been almost entirely swept away and the underlying rock has been cut into deeply by the discharge through the Cold Well Channel of the surplus waters of the glacial lake in the basin of the Burn of Finglennie. The floor of the Cold Well Channel now lies about 80 feet below the intake of b, erosion by the existing streamlet having been very slight indeed. Than the facts just mentioned no clearer proof could be obtained of the time relations between the Strathmore Ice and the Dee Valley Ice. Unfortunately the latter did not reach the intake of the Cold Well Channel, so that no granite overwash was carried by this route : consequently one cannot say whether, while the channel was in operation, the Old Red Sandstone and Downtonian areas to the south were or were not ice-free. It is clear, however, from the superposition of granite overwash on Strathmore drift along the lower Cowie that, before the maximum advance of the Dee Valley Ice, the Strathmore Ice had retreated south of Stonehaven—how far we do not know. 8. Carmont (or Carron) Channel. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 37

For over two miles after passing Carmont (New Mill) Station the Carron flows in a rock-bound gorge, in parts over 100 feet deep : it is well seen from the Caledonian Railway. The 400 feet contours run through the gorge and follow its brink for the better part of a mile ; here i.ts depth reaches a maximum. The stream is a glaring misfit, not because it could not have corroded its valley to the depth of the gorge but because, in the time required to do so, the valley walls would have been weathered back into gentle slopes. Previous to the Ice Age the Bervie-Carron watershed was a line connecting Carmont and Hill of Tannachie, and in the dip between these hills it fell to a level of somewhat over 400 feet. While the front of the retreating Strathmore Ice blocked the valley that runs south from Carmont Station, the meltwater from it passed across the lowest point on the watershed and began the erosion of the gorge. Even after the ice-front retired a considerable distance away from the southern end of the valley just mentioned, meltwater would still follow the same route—would indeed continue to do so until it could find exit from the Howe of the Mearns at a lower level, i.e., until the retreat of the ice uncovered the valley through which the Bervie Water turns eastward to the sea. Until that event, a glacial lake would be held up in the northern angle of the Howe of the Means and its surplus waters would pass through the Carmont gorge, the intake of which has an elevation of about 340 feet. It is evident from what has been said that the upper Carron (above Carmont Station) has been diverted from the Bervie. The overdeepening of the Carron gorge has given all the tributary streams that enter it a new local base-level of erosion and led to the excavation of post-glacial rock gorges along their lower courses. It is held by many that the essential condition for the forma­ tion of eskers is the presence of stagnant water in front of an ice-sheet or glacier during its retreat. Whether this be so or not, it is perfectly evident that the presence of the stagnant waters of a glacial lake would be extremely favourable to the preservation of eskers after the ice had retreated from them, since, being submerged, they would be protected from denuda­ tion by the run-off of meltwater from the ice-front. The kames, near DrumUthie (Kaim of Clearymuir, Kaims of Fiddes, Kaim of Candy), appear to be true eskers ; they do not rise anywhere much above 300 feet and must have been entirely submerged as long as the glacial lake existed. It is interesting to note that the axes of the kames point towards the intake of the Carmont Channel. They are casts of Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

38 EDINBURGH GEOLOGICAL SOCIETY. part of the subglacial stream of meltwater that, after issuing from the ice, was engaged in eroding the rock gorge. It may indeed be, as Dr A. R. Wallace suggested in the case of the Aar gorge, that the gorge itself is (partly) due to erosion by a sub- glacial stream. The existence of the glacial lake explains many peculiar features in the ground to the south and south-east of Drum- lithie ; but consideration of these would lead us beyond our district. Hawkill Den and Den of Kinmonth are overflow channels : to explain fully the causes that led to their formation would also lead us beyond our district. 9. Den of Luckyfeal and Craig Den. Together these curious marginal channels encircle the east and south shoulders of Carmont: they stand at different eleva­ tions, the former being the higher. Carmont had on its north and west sides the valleys of the tributary of the Bervie, since diverted into the Carron, and of the original Carron : from its east shoulder a long, flat-topped ridge curves round to the north-east. During one phase in the retreat of the ice the conical upper part of Carmont formed a nunatak and divided the ice-stream : one part just managed to surmount the flat-topped ridge and to the north-east reunited with the other which had come round by the west and north sides of the hill. It would seem that, owing to radiation from the nunatak, the ice stood at a lower level on the south than it did on the east shoulder of Carmont. From a watershed on the flat-topped spur marginal drainage descended north-eastward and south- westward and eroded the Den of Luckyfeal. The Den is separ­ ated into two parts by what looks like an artificial embankment —the divide between the two streams of meltwater.1 The marginal streams coursed between the ice and the slopes of the nunatak, and finally escaped under or through the ice. At their lower ends they formed lakelets, the sites of which are indicated by flattish areas dotted with small kettle-holes due to the entombment in detritus of detached blocks of ice. The Witch Pots, shown on the 6-inch maps, are quite typical kettle- holes. When the ice had shrunk still further, Craig Den was ex­ cavated, probably in two stages.1 By this time Carmont was no longer a nunatak and the meltwater escaped along the ice margin on the north-west side of the hill. The north wall of

1 The Den and the watershed are very clearly shown on the old edition of the 6-inch maps. 2 To the east of the main intake a shelf has been cut at a slightly higher level. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 39

Craig Den is composed of rock, the south wall mainly of moraine.

E. RAISED BEACHES AT STONEHAVEN. Between Craigeven Bay and Glenury Viaduct a considerable area is mapped as raised beach (^^): its average level is slightly under 100 feet. The line indicating " margin of denuded high terrace " encloses practically all the flat ground west of Stone­ haven, between the Cowie and Carron : this area is nearly a mile wide and its level varies from 100 to 120 feet above the sea. It may be assumed that the intention is to represent both these areas as belonging to the 100 foot raised beach. The supposed raised beach embraces so large an extent of ground (more than a square mile) that it is difficult to account for the entire absence within its limits of anything that can be called beach material. On its surface, and on the surface of what is definitely mapped as raised beach, we encounter red boulder clay, red brick clay,1 loamy sand, gravel with clay in its interstices, coarse glacial gravels—everything in fact but true beach deposits. It may be objected that the flats are a result of erosion only; but surely somewhere over so large a stretch of ground deposition must have taken place. Can any modern tidal flat of like extent be instanced on which, if it were elevated beyond the reach of the sea, no signs of marine action beyond mere erosion would be visible ? No shells have been found in any of the clays, sand, or gravels. The glacial gravels that form part of the Strathmore drift frequently present the appearance of beach material since the pebbles, derived from the conglomerates, are all well rounded : in places beds' of large beautifully-rounded boulders from this source suggest storm beaches. All the exposures of such beds within the probable limits of the 100 foot raised beach have been examined. The whole of them exhibit features that forbid our regarding them as beach gravels—occurrence of broken pebbles with perfectly unworn edges and of boulders of consider­ able size standing on end, and absence of all appearance of sifting and arrangement by sea waves, e.g., alternation of layers of clay and fine sand with layers of large pebbles, intermingling of clay and gravel, etc. In Stonehaven Bay the highest raised beach is absent. Much of the fine brick clay and loamy sand in the vicinity of Stonehaven—they occur mostly at and below the 200 foot level—may be explained as deposits in a glacial lake held up

1 On an exposed coast like that of Kincardineshire one does not expect either clay or unsifted loamy sand to occur as a beach deposit. Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

40 EDINBURGH GEOLOGICAL SOCIETY. by the Strathmore Ice at a time when it occupied the bed of the North Sea and blocked the mouths of the Cowie and Carron though it had retreated from the higher ground to the north and west. The lake may have discharged northward by the Den of Cowie Channel. At Broomhill Cemetery we find well-bedded sands and gravels, probably the undenuded remnant of a delta deposit formed where the meltwater which excavated the Carmont Channel entered the glacial lake. At Malcolm's Mount a section in these sands showed typical delta-bedding. They he above the margin of the supposed denuded terrace of the 100 foot raised beach. Within Stonehaven Bay the 50 foot raised beach is also wanting, but this may be because it has been removed during the formation of the lowest marine platform. The lower part of the town is built on the lowest raised beach. Beach deposits were beautifully displayed when the sewers were laid about forty years ago ; and, owing to recent changes, some good sections may be seen in the banks of the Cowie Water.

F. PREGLACIAL ROCK PLATFORM OR PLAIN OF MARINE DENUDATION. From Ruthrie Head to Cowie village the rock of the sea cliffs reaches a nearly uniform level of 75 feet. From Glenury Distillery round to the west of Glenury Viaduct a steep face of rock appears below the glacial deposits and rises to about the same height. All the way up the post-glacial channel of the Cowie to beyond Ury House the rock surface reaches a similar level, and the same is true of a small rock exposure north of Mill of Cowie. At the landward end of Garron Point, at Red Heugh and Downie Point, and again at Bowdun Point and Dunnottar Castle the rock of the sea cliffs, beneath a capping of glacial deposits, is planed off like that on the north side of Stonehaven Bay. From Ruthrie Head to Glenury Viaduct extends the area definitely mapped as raised beach. The flatness which has led to its being thus mapped is doubtless due* to the evenness of the* rock surface beneath. At no point is beach material seen to overlie the rock, so that the bevelling cannot be the work of the sea in post-glacial times : this is true of all the rock referred to above between Garron Point and Dunnottar Castle. It may therefore be suggested that the whole surface from the seaward edge of the exposed and evenly bevelled rock back to the first distinct rise in the ground is underlain by a preglacial Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015

THE GLACIAL GEOLOGY OF STONEHAVEN DISTRICT. 41 rock platform formed by marine denudation. This platform, breached by the preglacial valleys of the Cowie and Carron, probably extends beyond the limits that can be definitely fixed by noting outcrops of rock. North of Cowie village the breadth of the platform has been considerably reduced by later marine denudation. In post­ glacial times a second platform has been cut: it is just covered at H.W.O.S.T. So ineffective is marine erosion on the inner­ most part of this platform that slabs of shaly sandstone, de­ tached by atmospheric agencies from the cliffs above, may lie for years before they are pounded to pieces by the waves. The platform is probably in great part the work of the sea during the period when the lowest raised beach was in course of formation.

0. POSTGLACIAL DIVERSION OF THE COWIE AND CARRON WATERS. From Ury House to Glenury Railway Viaduct the Cowie flows in a rock gorge, which is clearly postglacial: the preglacial must lie to the south of the present course of the stream. Similarly, near Dunnottar Parish Church, the Carron has been thrown on to rock; but in this case the preglacial course is a little to the north.