Dr. D. Woolacott—Magnesian Limestone of Durham. 491 



that may be looked for, having a direct hearing on some of the 

 questions discussed in this paper. (1) Are concretionary and 

 segregated structures developed in the gypsiferous limestones? 

 (2) Are the gypsiferous beds demagnesified ? (3) Do gypsiferous 

 oolites occur? (Gypsiferous oolite was proved in the Newcastle 

 Chemical Works boring north of the Tees. The cores are now in 

 Middlesbrough Museum.) (4) Can the reef be traced southwards? 

 Strophalosia and Dielasma (both reef fossils) are recorded by 

 Trechmann in the Warren Cement Works boring at Hartlepool 

 from beneath the anhydrite. It should, however, be noticed that 

 the Magnesian Limestone as exposed in Yorkshire and further south 

 is a shallower-water deposit than that of Durham, so that the reef 

 may never be reached by borings through strata to the south of this 

 county. 



The Thrusting in the Northern Area. 



The northern area of the Durham Permian differs from the 

 southern in a more extensive brecciation and disturbance of the 

 strata. This results from the horizontal movements whicli can be 

 proved to have acted in the northern area, but which appear to have 

 had little effect in South Durham. Thus in the latter region 

 unshattered segregated rocks occur, while in the northern area these 

 rocks are usually brecciated. There is also much less general 

 deformation and disturbance of strata in the south than in the 

 north, and major and minor thrust-planes are not noticeable. 1 It is, 

 however, probable that many of the fissures which form a feature of 

 the middle and southern part of the Durham coast are tension 

 phenomena produced at the end of the period of thrusting, when the 

 pressures were relieved by the movement and the shattering of the 

 strata. 



The evidence proves that the horizontal movements, the effects of 

 which are so clearly exposed in the Coal-measures along the south- 

 east coast of Northumberland, 8 and the similar displacements 

 which have produced such marked structural features in the Permian 

 of South Northumberland and North Durham, were produced by the 

 same cause. The effects of the thrusting can be clearly seen at many 

 points along the coast from the north of Whitley to a few miles 

 south of Sunderland, a total distance of about 15 miles, and inland 

 on the Boldon Hills, at Claxheugh, and under the Sunderland 

 district over an area of several square miles. 3 Stratigraphically the 

 thrusting has affected several hundreds of feet of strata, and structures, 



1 It should, however, be noticed that the line of principal thrusting in the 

 north (i.e. the junction between the Lower and Middle Limestones) is not 

 exposed along the coast in the southern area. 



2 Lebour & Smythe, Q.J.G.S., vol. lxii, p. 530, 1906; Haselhurst, Proc. 

 "Univ. Durham Phil. Soc, vol. iv, pt. hi, p. 162, 1912; and Woolacott, 

 " Geology of N.E. Durham and S.E. Northumberland " : Proc. Geol. Assoc, 

 May, 1912. 



3 The thrust at Marsden is described in Univ. Durham Phil. Soc. Mem., 

 No. 1, 1909; at Claxheugh and on Down Hills in Trans. Nat. Hist. Soc. of 

 Northumberland and Durham, N.S., vol. v, pt. i, p. 155, 1919 ; and a detailed 

 account is given in my paper on the northern area of the Durham Permian, 

 Proc. Univ. Durham Phil. Soc, vol. iv, pt. v, 1912. 



