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ON THE GEOLOGY OF SOUTH-EASTERNKINCARDINESHIRE.

By ROBERT CAMPBELL, M.A., D.Se.

K I NCAR DI N ESH I R E is divided by the Highland faultinto two regions which in their geological and topo­

graphical aspects are markedly dissimilar. To the south isfound a tract occupied by rocks of older paleeozoic age-(?)Upper Cambrian, Upper Silurian (Downtonian), and OldRed Sandstone. To the north lies an area composedmainly of granites and Dalradian schists with a narrowinterrupted belt of the "boundary-fault series "-the (?) Arenigand Margie series of the Geological Survey-intervening betweenthe latter and the great fault. Excellent maps on the I inch and ;{inch scale have been published by the Geological Survey, whilethe boundary-fault series, the granites, and the aureole, ofmetamorphic rocks round the granite country have been ablydescribed by Mr. Barrow. Little, however, has been writtenabout the south-eastern portion of the country, and the presentshort note merely summarises results already published in theGeological Magazine. A fuller account of the stratigraphy ofthis interesting district was given recently in a communicationto the Royal Society of Edinburgh.

(?) UPPER CAMBRIAN.

Between Craigeven Bay and Garron Point, near Stonehaven,occurs a series of crushed green igneous rocks with associatedalack shales, jaspers, and cherts. In their lithological charactersthese resemble closely the (?) Arenig rocks of the GeologicalSurvey which are found at intervals along the Highland border.The black shales have yielded an interesting suite of fossils,including (a) hingeless brachiopods belonging to the generaLingule!la, Obolus, Acrotreta, Linnarssonia, and Siphonotreta;(b) several specimens of a bivalve phyllocarid allied to Caryocarisand Lingulocaris " and (c) cases of a tubicolar worm, thestructure of the tubes being like that of the modern Ditrupa.The above assemblage of fossils suggests that the rocks belongto either the Ordovician or Upper Cambrian, and, as Dr. Peachhas pointed out, the absense of graptolites points to the latteras the more probable horizon.

The (?) Cambrian rocks are separated from the Dalradianschists by a reversed fault which is probably a continuation of

296 ROBERT CAMPBELL ON

the Highland fault. On the south side of Craigeven Bay they areoverlain unconformably by Upper Silurian (Downtonian) strata.

UPPER SILURIAN (DOWNTONIAN).

Between Ruthery Head and Stonehaven harbour intervenesa thickness of nearly 3,000 ft. of vertical or highly inclinedsediments which were formerly regarded as belonging to theLower Old Red Sandstone, but are now considered to beDowntonian. The following succession may be studied inthe shore section;

(a) Basement breccias with interbedded thin sandstones andsandy mudstones (200 ft.).

The breccias are built up mainly of fragments of theCambrian strata. The unconformity is somewhat obscured byminor faulting and by the red staining of the underlying crushedigneous rocks, but detailed mapping has shown that it may betraced along the northern face of the headland at Ruthery Head,and thence in an easterly direction along the foreshore tolow-water mark. A reversed fault which crosses Ruthery Headshifts the outcrop of the lowest breccia 160 yds. to the south­west, and from this point the unconformity can be traced alongthe foreshore westwards.

(b) A series of purple sandstones (60 ft.).(c) Grey and brown sandstones with thin red mudstones

(1,000 ft.).(d) Volcanic conglomerate and tuffs (40 ft.).The boulders in the conglomerate are chiefly hornblende­

andesites and rhyolites; the tuffs consist of angular fragments ofthe same rocks.

(e) Red sandstone (60 ft.).(f) Grey sandstone and grey greenish fossiliferous sandy

shales and mudstones (with fish band, 600 ft.).

The grey and greenish mudstones are in places crowded withremains of Dictyocaris, along with which have been found Euryp­terus, sp. nov., Ceratiocaris, Archidesmus, and a new genus ofMyriopod, (1) larval form of insect, fragments of scorpion, plantremains, and worm tracks. Fish remains were first detected byDr. W. T. Gordon in a thin bed of reddish sandy mudstone,which underlies the Dictyocaris beds. They consist mainly ofbeautifully sculptured plates of a new C)'allzaspis. So far thecharacteristic fishes of the Downtonian of the south of Scotlandhave not been found.

(g) Tuffs and tuffaceous sandstone (800 ft.)The above beds pass up conformably into the sandstones and

conglomerates at Stonehaven harbour, which may be consideredas the base of the Lower Old Redstone.

THE GEOLOGY OF SOUTH-EASTERN KINCARDINESHIRE. 297

In its lithological aspects the above succession recalls at oncethe Downtonian rocks of the Pentland Hills and Lanarkshire,differing from these, however, in the presence of the volcanic con­glomerate and tuffs. The palzeontological evidence confirms thelithological. Dictyocaris and Ceratiocaris are both characteristicDowntonian fossils, and neither has been found in rocks youngerthan Upper Silurian. And, although the Downtonian fishes ofthe south of Scotland have not so far been discovered,Cyathaspis, as Dr. Traquair has pointed out, is more characteristicof the Silurian than of the Old Red Sandstone. The distinctivelithological characters, and the association of Dictyocaris, Cera­tiocaris, and Cyat/zaspis together appear to establish the age ofthese beds as Downtonian.

Inland sections of the Downtonian rocks may be studied inthe Carron Water and its tributaries.

LOWER OLD RED SANDSTONE.

The Lower Old Red Sandstone is composed of a greatthickness of coarse conglomerates and sandstones, among whichare intercalated several well-marked volcanic zones, the recognitionof which has proved of much value in elucidating the structure ofthe area. The palseontological evidence is so unsatisfactory thatlittle use can be made of it in correlating the rocks in differentparts of the district. The only locality in which fossils are at allnumerous is the Den of Morphie, near Marykirk, where Parkadecipiens is found in great abundance, and along with it Kampe­caris forfarensis and Fterygotus anglicus.

For many geologists the chief interest of the KincardineshireOld Red Sandstone lies in the extraordinary succession of coarseconglomerates. It is beyond the scope of the present note toenter on a discussion of the composition and meaning of these.It may be pointed out, however, that they fall readily into twowell-marked types, (a) conglomerates which are built up mainlyof boulders of volcanic rocks-" volcanic conglomerates," and(b) conglomerates in which the chief components are quartzites orother" Highland" rocks-" Highland conglomerates." Many ofthe latter, particularly in the lower part of the succession, arenoteworthy for the abundance of their boulders of jaspers andspilitic lavas, the presence of which points to the denudation ofwide areas of rocks identical in their lithological characters withthe Camhrian of Garron Point. A further point of interest maybe noted in the occurrence of boulders of the "Haggis rock"type of greywacke, closely resembling the well-known Haggisrocks of the Ordovician of the south of Scotland, and derivedpossibly from the Margie series of Mr. Barrow. The thickvolcanic conglomerates, with their predominating boulders of acidPROC. GEOL. Assoc., VOl.. XXIII, PART 5, 1912.J 25

298 THE GEOLOGY OF SOUTH-EASTERN KINCARDINESHIRE.

andesites and rhyolites, here again, as in the Downtonian, giveevidence of the denudation of a series of acid lavas, which musthave covered the area of Dalradian schists to the north of theHighland fault.

The contemporaneous lavas include flows of rhyolite, horn­blende-biotite andesite, hypersthene andesite, angite andesite, andseveral varieties of basalt. The tuffs are all acid. The associatedhypabyssal intrusions are chiefly in the form of quartz porphyryand lamprophyre dykes. The lamprophyres also occur as thinsills.

The main structural feature in the Lower Old Red Sandstonetract is a great synclinal fold, the centre of which is occupiedby the Howe of the Mearns-a continuation of the Plain ofStrathmore. In the district west of Elfhill there intervenesbetween the syncline and the Highland fault a steep-limbedanticline which pitches to the south-west. The southern limbof the syncline is traversed by a series of important dip faults.

UPPER OLD RED SANDSTONE.

Rocks of Upper Old Red Sandstone age are found in theneighbourhood of St. Cyrus. Their junction with the LowerOld Red is everywhere a line of faulting. No fossils have beenrecorded, but the lithological characters of the rocks, andparticularly the occurrence of typical comstones, show thatwe have here what is undoubtedly an outline of the moreextensive tract of Upper Old Red Sandstone of Arbroath.

LATER QUARTZ-DoLERITE DYKES.

The Quartz-dolerite dykes of the district, which have ageneral east-north-east and west-south-west trend are of thesame type, and probably belong to the same period of intrusion,as the well-known east and west dykes of the central valley ofScotland.

REFERENCES.

Geological Survey Map, Sheets 66,67,57, and 57a; 1884; revised, 1897.1882. PEACH" B. N.-"Fossil Myriopods from the Lower Old Red

Sandstone of Forfarshire." Trans. Royal Phvs. Soc. Edin.1897. GEIKIE, SIR ARCHIBALD.-" Ancient Volcanoes of Great Britain."

Vol. i,1901. BARROW, G.-" On the occurrence of Silurian (?) Rocks in Forfar­

shire and Kincardineshire along the Eastern Border of theHighlands." Quart Journ. Geol. Soc., vol. lvii, p. 328.

1908. HICKLING, G.-" The Old Red Sandstone of Forfarshire, Upper andLower." Geol. Mag., dec. v, vol. v, p. 396.

19Ir. CAMPBELL, R.-" Preliminary Note on the Geology of South-easternKincardineshire," Geoi, Mag., dec. v, vol, viii, p. 63.