316 Mr. N. Wood on the Geology of Northumberland, 8(c. 



vale of the Tyne we find (except where affected by Slip Dykes) the beds 

 pursuing a regular rise to the west, the lower beds successively cropping 

 out on the banks of the river ; and when we get beyond Prudhoe, we 

 reach in the vale, the lowest beds in the series. The full rise of the 

 strata is not however in the direct course of the Tyne, but north-west} 

 and as hills of considerable height occur on the south bank of the river, 

 the Coal beds stretch much further to the west along this ridge of hills, 

 and we consequently find workable beds on Hedley Fell. 



From this place a series of SHp Dykes, having a very considerable 

 throw to the north, stretches away westward by Stublick, Coanwood, 

 Hartley Barn, and Midgeholme to Tindal Fell. The course of these 

 Dykes is here interrupted by several cross slips, and they are made to 

 diverge south-west towards Croglin Fell ; though there is reason to 

 suppose that a continuation of the Main Dyke extends to the western 

 escarpment of the Mountain Limestone between Talkin and Castle 

 Carrick. 



The throw of these Dykes being very considerable to the north, pro- 

 ducing such a depression of the strata on the dip side, and their course 

 being along a ridge of hills which gradually increases in elevation west- 

 ward, we find on several of the eminences in different parts of their 

 course, detached portions of the lower beds of the regular Coal Mea- 

 sures thrown in, considerably beyond the western verge of the limits of 

 the Coal-field. 



No. 2, Plate XXVII., exhibits a section of these detached Coal-fields, 

 along the dip or north side of the line of these Dykes. The first of 

 these is Stublick, about 5 miles south-west of Hexham ; it extends for 

 about 4 or 5 miles along the dip side of the Dykes, from east of Spital 

 Shield, through Low and High Stublick, until it is cut off by the denu- 

 dation of the vale of the west Allen rivulet. In this as well as in the other 

 of these Coal-fields, the strata on the north side of the slip dip towards 

 the Dykes, which indeed is almost the universal concomitant of Slip 

 Dykes on the low or depressed side. The depth of the Coal-beds from the 

 surface at the Dykes is not great, and the rise of the strata from the slip 

 to the north causes the Coal to reach the surface within a few hundred 



