GEOLOGY OF PART OF SOUTH DURHAM. 187 



Rhynchonella pleurodon (?) Phillips. 

 Remains of Crinoids. 



We were at first inclined to look upon the limestone as the re- 

 mains of a large erratic boulder belonging to the Drift ; but a 

 careful examination satisfied us that both limestone and shale 

 were in situ. This opinion was corroborated on our subse- 

 quently discovering, further to the east, a similar limestone by 

 the side of the road that descends to Houghton-le-Side from the 

 north. The limestone there is seen about half way down the 

 hill accompanied by the same kind of calcareous shale as seen in 

 the quarry, and containing the same species of fossils as before 

 named. Beneath the limestone and shale follow a grey argilla- 

 ceous sandstone passing into an arenaceous shale, and a soft 

 grey shale, below which the strata are not shown. These beds 

 are not well exposed ; but sufficiently so, on both sides of the 

 road, to show that they are in their natural position. 



In connection with the dislocation, we may mention that 

 about a mile to the E.S.E. of Houghton-le Side, and at the foot 

 of the ridge that runs behind that place, the Magnesian Lime- 

 stone is seen in a quarry near to Broom Dykes (Toitup Quarry), 

 tilted up to the north at an angle of 60°, its usual inclination 

 being to the east at a low angle. 



Fig. 16. — Magnesian Limestone, Toitup Quarry. 



From these facts it appears clear that a fault with a down- 

 throw south passes along or near to the face of the ridge above 

 Houghton-le-side, which is of such magnitude as to bring in on 

 its rise side one of the calcareous beds of the upper portion of 



