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PROFESSOR T. J. JEHU AND DR ROBERT CAMPBELL ON 
The Highland Border Rocks include (a) a series of black and grey shales, cherts 
and cherty mudstones, with which are associated both volcanic and intrusive 
igneous rocks, and which are overlaid unconformably by ( b ) a series of grits and 
shales with calcareous bands. The general strike of the beds is north-east and 
south-west, the general dip to the north-west at high angles. The beds are often 
seen to be isoclinally folded along nearly vertical axial planes (Plate V, fig. 3). The 
whole belt is affected by crush lines, extending usually in the direction of the general 
strike of the beds. 
The Lower or Black Shale and Chert Series is made up of cherts, cherty shales, 
black and grey shales, and mudstones passing downwards into and interbedded with 
volcanic rocks of the spilitic type. The associated intrusive rocks include albite 
diabase, albite gabbro, and serpentine. Here may be included also a belt of highly 
metamorphosed rocks — hornblende schists, chlorite schists, and quartz schists, re- 
presenting respectively the intrusive igneous rocks, the lavas, and the siliceous 
sediments. 
The Upper Series, which may be termed the Margie Series,* consists of grits, 
shales, and limestone, and has a remarkable breccia at its base. The breccia is often 
richly charged with fragments of vesicular volcanic rock, a fact which points to a 
recrudescence of volcanic activity in the district at the time when the basement beds 
of the Upper Series were being deposited. 
For convenience of description detailed accounts of the above succession will be 
given in the following order : — 
(a) The Rocks of the Lower or Black Shale and Chert Series. 
(b) The Rocks of the Upper or Margie Series. 
(c) Palaeontology of the Beds. 
(d) The Age of the Highland Border Rocks. 
(e) The Intrusive Igneous Rocks. 
(f) The Hornblende-Schist Complex and Associated Sediments. 
IV. The Rocks of the Lower or Black Shale and Chert Series. 
The Spilitic Lavas. — The spilitic lavas, which are the lowest visible members of 
the series, are exposed at the surface only in. that part of the area which lies to the 
south-west of the Kelty Water. The best exposures occur in the upper course of the 
Corrie Burn, and in and near the most westerly of the two small tributary streams 
flowing down the eastern slope of Gualann. Other exposures are seen in the two 
small tributaries which join the Corrie Burn from the north-west. The spilites 
appear again at the surface in several rather poor exposures on the slopes of the hill 
north-west of a small tarn which is a noteworthy feature in the landscape just west 
of the new Loch Katrine aqueduct. 
* The term “Margie” has been applied to the Upper Series in Kincardineshire and Forfarshire by Mr Barrow, 
See Quart. Journ, Geol. Soc., vol. lvii, p. 328, 1901, 
