THE GEOLOGICAL STRUCTURE OF THE CANONBCE COALFIELD. 867 



sandstone, the Cementstone group, and by the Fell sandstones, which form a con- 

 spicuous eminence at Brownmoor Wood (d ,v ). These, in turn, are overlaid by the 

 members of the Marine Limestone series, which occupy the area southwards to the 

 margin of the Trias. At Kirtlebridge the limestones of the Lower Limestone group 

 (Penton Linns and Gilnockie) are exposed in various quarries, where they have been 

 extensively worked. Their outcrops show that the beds were folded in arches and 

 troughs before the deposition of the Trias, for the latter rests on the upturned and 

 denuded edges of the members of the Marine Limestone series (see section 5). It is 

 obvious, therefore, that in pre-Triassic time there must have been prolonged denudation 

 of the Carboniferous rocks in that region ; for all the divisions of the Canonbie Coal- 

 measures were removed, and the Marine limestones underneath the Kilnholm coals were 

 laid bare before the Triassic sandstones were deposited. 



Similar evidence is obtained in the Cadgill Burn, a tributary of the river Sark, about 

 half-way between Canonbie and Kirtlebridge. In that stream, within a few yards of the 

 margin of the Trias, there is a band of stained limestone, charged with encrinite stems, 

 Evomphalus carbonarius, Belhrophon, Maclirocliilina, and indeterminable fragments of 

 brachiopods, with stained sandstone containing modioliform shells. Here again the 

 Triassic sandstone rests on the upturned and denuded edges of the Marine limestones, 

 and the Coal-measures have been removed. 



Westwards beyond the Annan, at Kelhead and Clarencefield, the limestones of this 

 horizon appear. Much of that district is thickly covered with drift, but at the latter 

 locality the Marine limestone occurs within a mile of the margin of the New Red Sand- 

 stone, which points to transgression of the Trias and the removal by denudation of 

 the Coal-measures. 



IV. Estimate of Coal-supply in Concealed Coalfield underlying the Red 

 Sandstones of the Upper Coal-measures, North of the Triassic Rocks 

 at Canonbie. 



In the previous sections of this paper descriptive of the subdivisions of the Coal- 

 measures, the evidence has been given which leads to the conclusion that the Middle 

 Coal-measures of Byre Burn and the Lower Coal-measures of Rowanburn lie underneath 

 the Carboniferous red sandstones (d xul ). It was further stated that the area covered by 

 the latter amounts to two square miles. 



We have prepared the following estimate of the coal-supply of this concealed coal- 

 field on the basis that a seam of coal one foot thick and one square mile in area 

 contains 900,000 tons of coal : — 



Rowanburn Coals, estimated thickness 38 feet, . . 68,400,000 tons. 



Byre Burn Coals, estimated thickness 6 feet, . . 10,800,000 tons. 



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



