598 HEPORT— 1889. 



Granite lias long been known to occur in the heart of the Cheviots, but its full 

 importance was not recognised until Mr. Clough surveyed, and Mr. Teall showed 

 that the granite contained augite, and hence belonged to a type of rock rather rare 

 ill Britain. 



The greater part of the Cheviot area has been mapped by Mr. Clough. The 

 geological history of the district is briefly as follows : Over the floor of Silurian rocks 

 porphyrite lavas and ashes were erupted ; associated with the porphyrite there are 

 small patches of Lower Old Red Sandstone and Conglomerate. 



The porphyrites diifer in no essential respects from rocks of tertiary age, the 

 hypersthene-, augite-, and mica-andesites being all well represented ; the horn- 

 blende-andesites, however, are absent. 



Intrusive through the porphyrites are numerous dykes of granite, felstone, quartz- 

 felsite, and porphyrite ; whilst the central area is occupied by a large intrusive mass 

 of granite. 



The granite sends veins into the porphyrite, but is itself traversed by some of 

 the veins of felstone, porphyrite, &c., just mentioned. 



The granite is, therefore, later than the main volcanic outburst of the district, 

 but is earlier than some of the dykes. 



The dykes roughly point towards the central region, as though radiating there- 

 from. Mr. Clough suggests that some dykes which in certain parts are granite 

 become felstone or porphyrite dykes in other parts of their course.' The igneous 

 rocks of the Cheviots are then approximately of the same age, the granite forming 

 the core and central area of eruption. 



These igneous rocks are all earlier than the lowest Carboniferous or Upper Old 

 Red Sandstone, because the basement conglomerates contain fragments of Cheviot 

 porphyrite and granite, whilst no porphyrite or granite dykes are known to enter 

 the Carboniferous rocks. 



The Carboniferous Limestone Series of Northumberland is of considerable inter- 

 est, and it aflbrds the key by which the beds in Scotland have been correlated with 

 the typical areas in Central and Southern England. As shown in a paper by Mr. 

 Hugh Miller, read at the Birmingham meeting of the Association (Report for 1886. 

 p. 674), the classification proposed by the late G. Tate of Alnwick is applicable 

 generally, with only slight modifications, to the whole of Northumberland. 



The groups are, in descending order : — 

 Calcareous division. 

 Carbonaceous division. 

 Fell Sandstone series. 

 Cement- stone series. 



Lower freestones and basement conglomerates. 



The most striking physical feature is that at the base of the thick Fell Sand- 

 stones; these rocks form a range of craggy moorland throughout Northumberland, 

 much broken, however, by faults in many places. 



The top of the Fell Sandstones is less easily defined. 



The base of the Calcareous Division is taken at the Dun Limestone, which is now 

 known to be the same as the Redesdale Limestone of the centre and south of the 

 county. 



A well-marked horizon in the calcareous division is that of the great limestone, 

 known as the 10-yard, and Dryburn limestone in North Northumberland. Workable 

 seams of coal occur throughout the calcareous and carbonaceous division. 



The detailed mapping of the beds has enabled the Survey to trace a great number 

 of important lines of fault, the majority of which would have been unknown or at 

 least very imperfectly understood but for such survey. 



Amongst the special points of interest resulting from the survey of the Lime- 

 stone Series the following may be mentioned : («) A great part of the Calciferous 

 Sandstone Series of Scotland is the equivalent of the true Carboniferous Limestone 

 of central England; (b) The Scremerston coal seams must underlie the limestones 



' See C. T. Clough, 'Geology of the Cheviot Hills' (J/em. Geol. Sti7-vey,Sheetl08sE), 



1888. 



