52 Rev. A. Sedgwick on the Geological Relations and 



As examples tending to confirm what has just been stated, I may mention, — 1. That large 

 quarries are opened in various parts of the superficial rubble, which almost covers the plains 

 between Hartlepool and Stockton ; and that at Greatham and some other places in that district, 

 masses of magnesian limestone have drifted into the plain in great abundance, and are picked out 

 of the quarries and burnt for economical purposes. 2. That near Windlestone, Mainsforth, and 

 other places where small transverse valleys open through the limestone into the great plain, we 

 find the country almost covered with lofty irregular mounds of coarse gravel or dihivial sand. 

 3. That on the great plain which extends several miles on all sides of Darlington, we not only 

 meet with materials like those just described, but we find among them large water-worn blocks 

 which have been drifted from the mountains of Westmoreland and of Cumberland. 



These accumulations of diluvial matter are not, however, confined to the mere outskirts of the 

 limestone, or to certain portions of the great eastern plain. Between Embleton and Elwick they 

 begin to rise into elevated ridges; and from thence ranging about ten miles nearly due north over 

 the very centre of the limestone, they terminate at Wardenlaw Hill, in a capping about two 

 hundred feet thick, which is high enough to overlook all the eminences of the neighbouring 

 district*. 



Notwithstanding all these difficulties, Mr. Smith has given a good approximation (if we except 

 a small tract of country on the north bank of the Tees,) to the true line of demarcation. The 

 following short notices are all which I can add to the information which is conveyed on this head 

 by his county map. 



The rocks of High Coniscliff form the eastern boundary of the limestone on the north bank of 

 the Tees ; from thence the line ranges nearly due north, and appears to pass to the west of 

 Thornton, to the east of Ulmby, and to the west of Walworth. Near the last-mentioned place 

 the line seems to bear to the north-east, crosses the road leading to West Auckland about a quarter 

 of a mile south of the fourth milestone, and thence ranges on the south side of Bracks, and on the 

 south side of Aycliff, a little to the north of which place the ridge is interrupted by an extensive 

 tract of low marshy land. This low tract of land extends considerably to the north-west, and is 

 skirted by diluvial hills which approach near the western boundary of the formation. 



Nearly the whole breadth of the formation is cut through by the valley of denudation above 

 mentioned, which affords a passage for the new rail-road f. On the other side of it the range 

 appears to be nearly due north towards Windleston, where every thing is buried under heaps of 

 diluvial gravel. 



* A detailed description of these diluvial masses does not come within the objects of this paper ; 

 but it may perhaps be worth while to state, that, in addition to a well known spheroidal block of 

 Shap granite, about four feet in its longest diameter, which lies in one of the streets of Darlington, 

 many other boulders of the same rock are found on the Yorkshire side of the Tees ; that they 

 occur in the village of Barton by the road side north of Newton, and in the river Tecs close to 

 Pierce Bridge; and that similar granite pebbles and boulders abound in a diluvial cliff further 

 down the river. That at Wardenlaw Hill (which reaches an elevation of about eight hundred 

 feet) the diluvial cap above mentioned contains rocks which have been drifted from all the neigh, 

 bouring districts, mixed with masses of granite, syenite, micaceous slate, greenstone, &c. &c. 

 some specimens of which it would be difficult to refer to their native seat. 



The average thickness of the apparently diluvial hills which terminate at Wardenlaw would be 

 difficult to determine, as they rest upon a very uneven surface of limestone. Close to Castle Eden 

 they lately bored to the depth of twenty-six fathoms without reaching the bottom of a series of 

 beds of loam, clay, and gravel, which appear to fill up a natural depression of the limestone. 



t On the south side of the denudation through which this new rail-road descends from the 

 West Auckland coal-field, no limestone is visible in situ ; but it probably passes to the north 

 side of the road under a cover of diluvium, near Midderidge quarry. 



