TRANSACTIONS OF SECTION C. 599 



in South-eastern Berwickshire ; (c) The same seiies of coals must he brought in by an 

 important synclinal in the valley of the Till between Chillinsrhain and Wooler ; 

 (d) The Lewisburu and Plashetts coals occur (as do the Scremerston seams) in the 

 Carbonaceous division ; (e) The discovery of an important t'uuna and flora in the 

 cement-stone series of Northumberland, hitherto believed to be but sparsely fossili- 

 ferous. Over sixty species, including twelve plants, have been collected. Several 

 new plants have been described by Mr. Kidston. lilight new schizopod crustaceans, 

 and two or more scorpions, have been determined by Mr. Peach.' 



The true Carboniferous Limestone fauna is especially characteristic of the lime- 

 stones of the calcareous division, the shales and the ironstones of that division 

 containing- genera peculiar to tliemselves. Some beds of limestone are much more 

 fossiliferous than others, and locally may be characterised by special fossils ; but 

 palaeontology cannot be relied upon for "fixing positions in the calcareous series. 

 Saccaminiita Carteri, supposed when first discovered to be confined to the four- 

 fathom limestone, is now known to have a much wider range. 



The lowest beds of the Carboniferous Series are coarse conglomerates ; these 

 are not continuous deposits, but seem often to have accumulated in .sheltered hol- 

 lows or bays. They are not always on the same horizon, but form local ' base- 

 ment-beds.' That overlying the Silurian rocks of Teesdale is about 1,500 feet 

 higher in the series than the basement conglomerate in parts of the Cross Fell 

 escarpment. 



The thickness of the various divisions varies much. The Fell sandstones attain 

 their maximum thickness of about 2,000 feet at the Simonside Hills; they thin to 

 about 500 feet to the west and north. The carbonaceous series attains its maximum 

 thickness of nearly 3,000 feet in North Tynedale ; the calcareous division its maxi- 

 mum (of about 3,500 feet) near the Wansbeck. The cement stone series is thickest 

 west of Rothbury and again near the Tweed ; in both districts it is about 1 ,500 feet 

 thick. The limestones of this series are most fully developed west of Rothbury. 



As regards the Coal-measures the Survey has, for the most part, merely been 

 able to collect information from the mining engineers, and to trace the outcrops of 

 the more important seams. The history of the coal-field was well worked out 

 before the Survey came into the district. Perhaps the part least known was that 

 north of the Wansbeck, and even now there are areas here as yet only partially 

 understood. One of the most important seams north of the Wansbeck is the 

 Ashington or Longhirst main seam. This was shown by the Survey to be the 

 equivalent of the Grey seam. 



The highest Coal-measures do not occur in the district ; there is here a strong 

 unconformity between the Carboniferous rocks and the Permian beds ; the latter 

 in South Durham sweeping over the edges of the former until they rest on the 

 Carboniferous Limestone. 



The occurrence of rock-salt in the lower part of the Triassic rocks near the 

 Tees is a most important point in the geology of the district, but that question is 

 fully dealt with by Messrs. Marley and Lebour in another paper. 



Contemporaneous basaltic rocks occur in the lower part of the Carboniferous 

 Limestone Series in Liddlesdale, in Cottonshope, Spithope,etc., and near Carham; 

 but they are better developed on the Scottish side of the Border. They lie between 

 the lower freestones and the cement-stone series. 



The intrusive basaltic rocks occur in two forms — as ' sills ' and as ' dykes.' The 

 sills are sheets of basalt, lying in and between the sedimentary strata in such a 

 manner as to have led some observers to believe the beds of trap to be contempora- 

 neous; but evidence of intrusion is abundant elsewhere, and the basalt lies at very 

 different horizons in different places. The Whin Sill usually occurs within the lower 

 half of the calcareous division, but in North Northumberland it goes lower. In the 

 south-west of the county, in the faulted coal-field of Midgeholm, a sill of basalt 

 occurs in the Lower Coal-measures. The age of the Whin Sill is not known ; it is 

 probably late Carboniferous, or a little later. There is every reason to believe it to 

 be pre-triassic. 



' See Hugh Miller, 'Geology of Otterburn and Elsden ' (J/cm. Geol. Survey, 

 Sheet 108bE), 1887. 



