NOETHUMBEELAND AND DURHAM. 15 



tlie liighest stratum of Allenlieacls ; and beds of tliis group appear 

 on Kilhope Law at an elevation of 2206 feet, and on the top of 

 Cross Fell, which is 2901 feet above the sea-level. 



4. The Coal Measures which overlie the Millstone Grit, oc- 

 cupy, in IN'orthumberland, the triangular area having the Tyne 

 as a base line 14 miles in length; its eastern side is the coast, 

 from the mouth of the Coquet to Tynemouth, and its western 

 side a wavy line from the Coquet mouth to near Wylam on the 

 Tyne. From this base line they extend into the central por- 

 tion of the county of Durham ; and by a fault called the Stub- 

 lick Dike they are prolonged, in a narrow band up the valley of 

 the Tyne to the extremity of the county of Northuniberland, and 

 into Cumberland, a distance of 27 miles. The whole length of 

 this coal field is about 55 miles, having an area of about 700 

 square miles, marked by undulating ground of moderate eleva- 

 tion rising gently to the west : the highest hills northward of 

 the Tyne are nearly 400 feet, but some in Durham attain to 740 

 feet above the sea-level. 



In these Coal Measures there is almost a repetition of the same 

 characters we find in the Carbonaceous group of the Mountain 

 Limestone, with this exception, that while there were marine 

 relics and a few thin limestones in the earlier period, limestones 

 are altogether absent from the Coal Measures, and there are 

 scarcely any indications of marine conditions. The sandstones, 

 shales, and ironstones are similar in both ; but in the more re- 

 cent period the coals are thicker, richer, and more bituminous. 

 From the variable thickness of the coal-seams in difi'erent parts 

 of the field, and from some seams being split into two by the in- 

 tervention of shales, of greater or less thickness, it is difiicult to 

 coiTelate the seams in distant parts of the field. There appear, 

 however, to be in all fifty-seven seams, having an aggregate 

 thickness of about 80 feet ; but as several are thin, only twelve 

 are workable, yielding about 50 feet of good coal. The Three- 

 quarter Coal, which is of poor quality, crops out in the Ouse- 

 bum ; the High Main, one of the best for domestic use, is ^\ feet 

 thick, and crops out on the declivity of the hill leading to Denton 



