Eyemouth - an excursion
O.S. 1:50 000 Sheet 67 Duns and Dunbar
- 1 Introduction
- 2 Excursion A. West of Eyemouth
- 3 Excursion B. East of Eyemouth
- 4 References
On this excursion the coastal exposures at Eyemouth are examined, over a distance of some 5 km, and an optional inland diversion covers some of the ground south of the town. Eyemouth lies about 12 km north-west of Berwick-upon-Tweed and is reached from the A1 road by the A1107 road from Burnmouth 4 km to the south-east from Ayton, 4 km to south-west or from Cockburnspath 20 km to the north-west. Cars and coaches may be parked on the esplanade, west of the river (busy in summer), or on the east side of the river near the harbour mouth and the golf course.
The coastal excursion falls into two parts separated by the town, and by the Eye Water, which follows approximately the line of a major NNE fault. The rocks to the west are Lower Devonian volcanics with an overlying outlier of Devono-Carboniferous age, best examined when the tide is low, whereas those to the east are Silurian greywackes. The excursion as described begins and ends at the esplanade car park. The distances involved are:-
- west of the town - 3 km, mainly on roads and cliff-top paths, 1 km of it on rough rocky shore
- east of the town - 6 km divided about equally between roads and cliff-top paths, with short rocky traverses at the numbered localities; the Redhall diversion adds 1.7 km on roads and across fields
Excursion A. West of Eyemouth
1. Killiedraught Bay: Volcanic Vent
From the car park follow the road westward for 300 m then turn right into Pocklaw Slap, through a modern housing estate. Continue in a north-westerly direction for 500 m to reach the cliff-tops, beyond the end of the road, in the southern corner of Killiedraught Bay. The rocks in the bay are considered to lie within a volcanic vent, and detailed exposures may be studied by descending a path from this point north-westwards to the shore. Otherwise the cliff-top should be followed northwards, to the right. The vent-rocks are agglomerates of variable coarseness, and igneous rockswhich in some cases have the texture of extrusive andesite and resemble undoubted lavas to be seen nearby to the east. Their outcrop extends 700 m along the shore, north-westward to Callercove Point, and lacks any obvious internal pattern
2. Hairy Ness : Lava and Agglomerate
3. Eyemouth Fort: Upper Old Red SandstoneTo the east the cliffs below Eyemouth Fort are capped by a brighter red rock, a coarse conglomerate with bands of sandstone, of the Devono-Carboniferous Upper Old Red Sandstone. On a northward promontory near the western end of the outcrop 12 m of this rock is exposed, overlying slabby-jointed purple lava in the lower part of the cliff. The sediments consist largely of conglomerate, including angular fragments of purple lava and pale green sandstone, with a lenticular bed of cross-bedded sandstone between 2.5 and 5 m. from the top.
The lavas to the south are predominantly agglomeratic and include brecciated dacite, the most acid of all these St Abbs-Eyemouth rocks. It is well exposed on a minor promontory below the southern limit of the conglomerate, where it is developed as an accumulation of disoriented subangular blocks of rather soft greyish rock with prominent flow-oriented small feldspars. Small knots of malachite occur locally. This auto-brecciated lava is highly homogeneous, but the exposures scattered across the foreshore to south consist most commonly of blocks of lava embedded in an igneous matrix C At one point on the cliff the volcanic rocks are channelled by a sequence of gravel and sand 10 m thick, overlain by 3 m of boulder clay. The lower deposits, in part clearly stratified and showing some rounding of pebbles, are considered to mark the course of a stream prior to the last (Devensian) glaciation.
Excursion B. East of Eyemouth
For the part of the excursion east of Eyemouth vehicles may be most conveniently parked on the east side of the harbour, near its mouth and the old mansion of Gunsgreen (NT 9475 6437), reached by turning left off the road to Berwick immediately after crossing the river. Gunsgreen can be reached on foot from the town by following the quays round the harbour.
The Silurian rocks which occupy the coast between Eyemouth and Burnmouth are greywackes and siltstones of the Hawick Group, highly folded and faulted, occurring in beds generally less than 1 m thick and notably thinner than in the Fast Castle Gala Group outcrop. The Hawick Group rocks are also on average more finely grained, have a higher proportion of quartz grains to feldspathic and lithic fragments, and are more commonly bound by a calcareous cement. Interbedded red mudstone is also a characteristic feature of the Hawick Group succession in the Eyemouth area. The folding of the Eyemouth rocks is more complex than the relatively simple succession of broad synclines and anticlines which characterises the northern outcrop. The dominant pattern of NW-SE (Caledonoid) compression continued, but superimposed on it was contemporaneous sinistral strike-slip shear vector; the combined effect was a system of fold hinges showing marked changes in plunge along their length. Some spectacular examples of hinge plunge variation are seen in the Eyemouth section. It should be stressed that they are not the product of two discrete superimposed fold episodes but rather record the variable interaction of compressive and strike-slip movements. However, there are some examples of steeply plunging hinges about which the cleavage and more gently-plunging hinges are folded. These steep structures are related entirely to the strikeslip shear event and usually have a sinistral sense. Sedimentation structures are similar to those described in the Fast Castle rocks, and the main source of sediment appears statistically to have lain to ENE. No fossils have yet been recorded from this outcrop, a feature which, added to certain lithological characteristics, reinforces the correlation with the Silurian Hawick Group of other parts of southern Scotland (Greig 1988).
4. Elgy Rocks: Folded Greywackes
From the east side of the harbour climb up to John's Road, at the left-hand end of a modern housing estate, then follow to the east a vehicle track along the landward side of playing fields. These fields occupy gravel flats which can be topographically linked with fluvial terraces along the course of the Eye Water, laid down when drainage was impeded by the presence of thick sea-ice. Continue on this path to the cliff-top, then turn northward for 200 m to the headland of Elgy Rocks. On this short traverse many folds will be seen. These are generally tight structures whose limbs dip steeply to NNW and more steeply to SSE, the fold axes plunging at 45° to WSW. Northwards, open folds are more common and their axes plunge less steeply. For example, Elgy Loch, the inlet immediately south-east of Elgy Rocks, follows the hinge line of an anticline with limbs dipping at 65° to NNW and 57° to SSE and an axial plunge of 25° to WSW. Synclines similarly oriented are developed at 10 m distance to NNW and SSE. The headland of Elgy Rocks is cut off from the mainland by a narrow fault-gully at right angles to these structures. On its landward side is seen the broad crest of an anticline, which forms the south-eastern side of the headland, some of the beds being modified by transverse-current ripple-marks which happen to coincide in direction with the fold axes and have in consequence been exaggerated to form prominent mullion-like structures 10 cm wide. At most states of the tide there is little difficulty in scrambling across the gully to Elgy Rocks, (but beware of being isolated for an hour or two by a rising tide). A plethora of folds is developed, similar in orientation to those noted on the cliffs to south. The development of folding varies along the strike, one series of 11 folds in a15-m traverse being represented 75 m to south-west by a single open syncline. Near the headland 18 folds occur in a 50-m traverse. Exceptionally spectacular folding is displayed on a seaward rock-face just north-east of the gully. The major feature here is a near-isoclinal anticline inclined steeply to NW, apparently thrust up from NW across strata in which two vertical isoclines are developed. The thin beds to south-east of the major fold are less tightly folded but all dip to NW, in sympathy with the overthrust movement.
5. John's Roads and Agate Point: Folded Greywackes
These structures were first described in detail by Dearman and others (1962, p.279), as were those at Agate Point, 100 m to east, where a close series of folds on NE axes also exhibits extreme and locally abrupt variations in plunge. Where the plunge is to NE the folds are seen to be downward-facing, in contrast to upward-facing folds which plunge towards SW. Vertical fold hinges are locally prominent, and faults are abundant both, across and parallel to the fold trend. As at John's Roads, and more obviously here, the secondary overturning of the folds is from NE to SW. At neither locality are the details of structural complexity immediately apparent. Towards the south-east side of Agate Point, and for 200 m to the south, several intrusions of porphyrite or lamprophyre may be seen. They vary between 30 cm and 1 m in thickness and some are not readily distinguishable from the greywackes, being approximately concordant with the bedding.
6. Whalt Point - Dove Cave: Folded GreywackesSouthwards from the complexities of Agate Point to Whalt Point the strata are more regularly folded, with hinge plunges between 75° SW and vertical.
7. Scout Cave: Dolerite Dyke
From the cliff-top near Whalt Point the southward traverse is resumed for 500 m to the headland above Scout Cave, at which point the Silurian rocks are cut by a quartz-dolerite dyke, 40 m wide. The massive rock, locally very deeply weathered, is readily distinguished and is exposed in places to WSW for 300 m. (Its position on the cliffs below is marked by a cave, not discernible from the land.) This dyke is one of a suite of Late Carboniferous or Permian age which occurs widely in central and south-eastern Scotland, other local examples occurring at St Abb's harbour and in the Burnmouth district.
8. Hurker's Haven: Porphyrite Sills
Some 700 m south of Scout Cave, at Blaikie Heugh, a small old quarry lies just below the cliff-top, its landward face defined by a sill-like intrusion of porphyrite, 1.5 m thick. The 12 m of greywackes and shales within the quarry, are purple-stained and unusually red-weathered. Another porphyrite sill is exposed at Hurker's Haven, to the east. The shore of the Haven can safely be reached down steep grass on its southern side. An acid porphyrite sill, 6.7 m thick, forms a minor promontory in the middle of the beach and a similar thinner intrusion is seen 50 m to west, close to the western corner of the bay, over a distance of at least 150 m above and below H.W.M. These sills, like those near Agate Point, belong to the Siluro-Devonian suite, oriented between N and NE, which has been noted in the St Abbs and Coldingham areas and is particularly profusely developed in this area, from Agate Point to Lamberton Moor (NT 96 59). The sediments in Hurker's Haven and eastward to Fancove Head exhibit the repeated fold pairs noted at Whalt Point. Good examples occur of flute-casts, groove-casts, and transverse-current ripple-marks, and minor faults are clearly displayed. From the cliff-top the return to Eyemouth may be varied by following a field-track from behind the quarry at Blaikie Heugh for 600 m to the A.1107 road. The car park at Eyemouth is 2 km further by road. Good exposures of convoluted fluvio-glacial sands and clays were seen near the road junction (NT 943 629) south of Netherbyres when the A.1107 was re-aligned.
9. Redhall cutting: Dykes
An additional diversion may be made from this junction along the road to the Redhall Cottages, thence north-westward to the disused railway line. In the cuttings to north the greywackes are seen to be cut in places by rather leucocratic sill-like intrusions several metres thick. Examples occur 60 m, 150 m and 300 m north of the footbridge west of the cottages. The last of these intrusions is in contact, to the north, with a 30-m quartz-dolerite dyke, thought to be that at Scout Cave. (This dyke forms the prominent bluff of Kip Rock (NT 9395 6265) just to west, where it is well exposed in the bed of the Ale Water 500 m further west). From this point on the railway line the road 150 m to east can be reached for the return to Eyemouth. To the north the fields west of the road occupy a series of well-defined fluvial gravel terraces, of the suite noted at the playing fields (locality 4).
- The headland of Hairy Ness may be taken as the first locality, reached by a shorter path along the seaward side of the large caravan site, between it and Eyemouth Fort.
- Greig, D.C. 1988. Geology of the Eyemouth district. Mem. Brit. Geol. Surv. Hutton, J. 1795. Theory of the Earth. William Creech, Edinburgh.
- Dearman, W.R., Shiells, K.A.G.,and Larwood, G.P. 1962. Refolded folds in the Silurian rocks of Eyemouth, Berwickshire. Proc. Yorks. Geol. Soc. 33, 373-268.
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