Downloaded from http://trned.lyellcollection.org/ at University of California-San Diego on June 8, 2015 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 <Condomerates # Volcanic RocKs j t Except 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.