Vol. 67.] OF THE PERSIAN OF NORTH DURHAM. 315 



if it were now found that the original ' breccia-gashes ' had had an 

 entirely different origin. 



Mr. G. W. Lampltjgh recalled the overthrust in the Chalk on the 

 north side of Elainborough Head, which resembled some of the 

 disturbances described by the Author, and deserved consideration 

 in discussing the ago of earth-movements on the north-east coast. 

 He further mentioned that a succession comparable to that of 

 Durham could be traced in the Magnesian Limestone Series of 

 North-East Derbyshire ; but the subdivisions in the two districts 

 may represent equivalence of phase, without exact equivalence of 

 time. He enquired whether the Author had observed any dome-like 

 structures among the more massive limestones of Durham, as such 

 structures were conspicuous in parts of Eastern Derbyshire and 

 appeared there to be due to conditions of deposition. 



The Author thanked the Eellows present for the manner in 

 which they had received his paper. He also expressed his thanks 

 to Mr. S. E. Haselhurst, M.Sc, for making the model of the 

 district shown, and to Mr. C. T. Trechmann, B.Sc, for some of 

 the specimens of fossils lying on the table. He agreed with 

 Prof. Garwood's suggestion that sometimes the magnesium carbonate 

 may have been removed by the mechanical action of water ; but 

 some of the cellular forms described had certainly been produced 

 by chemical action. In reply to Mr. Dixon, he stated that, under 

 certain conditions of temperature and pressure, magnesium carbonate 

 (in the presence of calcium carbonate) was the most soluble of the 

 two salts. He emphasized the need for a thorough study of the 

 relative solubilities of these two carbonates in presence of one 

 another, and of such other substances as must have existed in the 

 Permian sea. Both these speakers had referred to the ' breccia- 

 gashes ' : he was convinced that the vertical ' breccia-fissures ' had 

 been produced at the end of the period of thrusting ; but some of 

 the triangular ' breccia-gashes ' may have been caused by the 

 falling-in of caverns, formed by the mechanical removal of softer 

 beds or by their solution. 



The thrusting in the Permian appeared to be directed towards a 

 central area ; the accentuation of the Coal-Measure basin of North- 

 umberland and Durham beneath East Durham, as also the synclinal 

 form of the Permian strata in the same area, was probably produced 

 by it. That it was connected with some general movement of the 

 North-of-En gland strata, as suggested by Prof. Garwood, seemed 

 certain. The Author regarded it as having taken place between 

 the Cretaceous and the Miocene Periods. 



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