326 Mr. N. Wood on the Geology of Northumberland, ^c. 



of this line of Dykes, their raineralogical character scarcely entitles them 

 to a distinct appellation. At the bottom of the Coal Measures there cer- 

 tainly occur thick beds of Gritty Sandstone, containing imbedded frag- 

 ments of large and angular Quartz ; but these grits are not more coarse, 

 and they are not otherwise more particularly distinguishable, than several 

 of the Sandstones belonging to the Lead Measures, and even not more 

 than some of those of the regular Coal Measures. If these beds are, 

 therefore, entitled in this district to a distinctive name, as part of a 

 general formation, they must be here characterised as thick beds of 

 coarse Gritty Sandstone, almost entirely destitute of mineral products, 

 lying between the bottom of the Coal Measures and the first Limestones 

 of the Carboniferous series. It is rather difficult to say where the lower 

 limit of this formation should be fixed — perhaps, most properly, at the 

 first bed of Limestone. It certainly should not be below the seam of 

 Coal of Talkin, Shilbottle, &c., as the next Limestone below is that, 

 which, according to Westgarth Forster, " has produced as much 

 Lead Ore as all the other strata throughout the whole Section." I have, 

 therefore, coloured the Millstone Grit as terminating at the second bed 

 of Limestone, or along the range of the bed of Coal previously traced 

 throughout the district ; if it is made to terminate at the first bed of 

 Limestone, the line would be about the middle of that range. 



On examining the range of the first Limestones and the superim- 

 posed Gritty Sandstones, it appears that they dip not only underneath 

 the regular Coal Measures, where the great body of that deposit exists, 

 but it will be seen that these beds also stretch away westward and dip 

 under these detached Coal Basins, thus proving the real position of the 

 latter in the series. See Plate XXVII. 



I shall now endeavour to trace some of the lower beds of the series, 

 or the great central beds of Limestone, with reference more particularly 

 to the position of the thick and numerous seams of Coal occurring near 

 the mouth of the Tweed. 



The bed of Coal worked at Geltsdale, &c., has been traced eastward 

 throughout the district to Shilbottle ; this bed of Coal is stated to lie a- 

 bove the great Limestone, and, therefore, the range of the one will exhibit 



