THE GEOLOGICAL STRUCTURE OF THE CANONB1E COALFIELD. 859 



Lithologically, as Mr Binney pointed out, the sandstones, marls, and clayey shales 

 of this Carboniferous subdivision are distinguishable from the Triassic rocks to the south. 

 Much of the red and purple colour of the former is due to staining, and they lack the 

 rich brick-red hue of the Triassic sandstones. This contrast is very apparent in the 

 Esk. Eeference has already been made to the fact that Mr Binney detected in the Esk 

 at Knotty holm a bed of Spirorbis limestone, six inches thick, in association with red 

 and purple shales, clays, bands of grit, and two seams of calcareous ironstone. 



The plants obtained by Mr Macconochie from the red and greenish shales in the 

 upper part of this series at Jockie's Syke, near Biddings Junction, have been un- 

 hesitatingly referred by Mr Kidston to the horizon of the Upper Coal-measures.* In 

 the absence of determinable plants from the members of this group exposed in the Esk 

 section, he is at present unable to determine whether the latter belong to the Upper 

 Transition series of England or to the Upper Coal-measures. 



Along their southern margin these Upper Carboniferous sandstones are covered 

 unconformably by the Trias, the boundary between the two being a sinuous line. As 

 shown on the sketch map (Blate I.), they occupy on the Scottish side a narrow belt 

 about three miles in length from the Liddel westwards beyond the Esk. Owing to the 

 thick accumulation of drift (boulder clay and gravel), their limits west of the Esk cannot 

 be definitely fixed, but it is probable that they extend as far as Bulmans Knowe, which 

 is about a mile west of that river. On this assumption the area which they cover in 

 Scotland is two square miles. 



A question of great economic importance arises in connection with this highest 

 division of the Carboniferous system in the border region, which relates to the 

 existence of a concealed coalfield underneath the area occupied by these sandstones. 

 There is no evidence at present known to us pointing to any unconformability at their 

 base ; indeed, all the available data indicate continuous deposition from the Whita 

 sandstones and cementstones to the top of the system. Under these circumstances it 

 is obvious that both the valuable coal-seams of Bowanburn and those of Byre Burn 

 might naturally be found below these sandstones. With the view of testing this 

 question, the representatives of His Grace the Duke of Buccleuch sank two deep bores. 

 The first was put down at Bowanburn about 200 yards south of the great fault that 

 bounds these sandstones on the north (see Plate I.). A copy of the journal of this 

 bore is given below : — 



* Summary of Progress, H.M. Geological Survey, 1902, p. 214. Trans. Roy. Soc. Edin., vol. xl. pp. 741-833. 



TRANS. ROY. SOC. EDIN., VOL. XL. PART IV. (NO. 32) 6 ji 



