THE GEOLOGICAL STRUCTURE OF THE CANONBIE COALFIELD. 869 



that Tate's classification applies not only to north Northumberland, but to north-east 

 Cumberland, Liddisdale, and Eskdale. 



The foregoing order of succession is exposed in clear sections in the basin of the 

 Tweed near Berwick, and along the shore to the south-east of that town as far as 

 Cheswick, which we had an opportunity of examining this year. 



The conformable passage from the Upper Old Ked Sandstone through the con- 

 temporaneous volcanic rocks of Kelso, which at Carham are overlain by a prominent 

 band of cornstone, into the overlying Cementstone group, is well seen in various 

 streams, as for instance in the tributary of the Whiteadder near Preston, west of 

 Edrom. Throughout the Merse of Berwickshire there is an extensive development of 

 the Cementstone group, where they consist of green, grey, and red shales and clays, 

 sandstones, and pale argillaceous limestones and cementstones, which, save on certain 

 horizons, rarely yield fossils. Plant remains occur in some of the beds, but there are 

 no coal-seams. No limestones, similar to those at Larriston and Thorlieshope in 

 Liddisdale, with corals, brachiopods, and other organic remains indicating open sea 

 conditions, have yet been found in the Cementstone group in the Merse. The fauna 

 is largely estuarine, the characteristic form being Modiola Macadami. In the higher 

 part of the group in the Tweed, near Coldstream, lamellibranch limestones, with 

 Orthoceras, Pleurotomaria, fish-remains, scorpions, and crustaceans occur. Similar 

 evidence is obtained at the head of Redesdale, where one of the limestone bands near 

 the top of the group is richly charged with lamellibranchs, together with Orthoceras 

 and Rlnjnchonella* 



The district south of the Tweed from Norham and Berwick, south by Lowick to 

 beyond Belford, was accurately mapped and described by our late colleague Mr Gunn, 

 where the order of succession is remarkably clear. On the slope overlooking the 

 Tweed between Norham and Berwick, the Cementstone group is surmounted by the 

 Fell sandstones, which in the north-east part of that area reach a thickness of 300 feet, 

 but gradually swell out towards the south-west to 600 feet. Next in order come the 

 members of the Carbonaceous group (Scremerston coals), with several workable coal- 

 seams, the outcrops of which are laid down on the Geological Survey maps (sheets 110, 

 N.W., N.E., old series, England and Wales). The average thickness of this division was 

 estimated by Mr Gunn at 800 feet.t 



The Scremerston coals and associated strata are followed in normal secpience by the 

 Calcareous division, which, according to Tate's classification, as already indicated, 

 embraces all the beds from the base of the Dun Limestone to the base of the Millstone 

 Grit. The Calcareous division has been further classified into a Lower Calcareous 

 subgroup, including the beds from the base of the Dun Limestone to the top of the 

 Dry burn Limestone (1480 feet),| and an Upper Calcareous subgroup comprising the 



* Mem. Geol. Sure, — Geology of the Country round Otterburn and Elsdon, p. 10. 

 t Ibid., Geology of the Coast south of Berwick-on-Tweed, p. 4. 

 J Ibid., p. 17. 



