194 



T. TRECHMANN ON A MASS OF ANHYDRITE [J uue l 9 l 3> 



Hartlepool Harbour occupied laterally a very much more extended 

 area when it was originally deposited; also that it has been 

 gradually reduced in size, and represents in fact the last remnant 



of anhydrite formerly common 

 to the whole formation, its great 

 size and thickness having saved 

 it from complete removal. 



One of the objects of this 

 paper is to demonstrate that most 

 of the changes and vicissitudes 

 undergone by the Magnesian 

 Limestone are due to the sub- 

 sequent removal of sulphates 

 from the formation. These sul- 

 phates "were originally present, 

 both as interstratified beds and 

 lenticles, and also impregnating 

 and in very close association 

 with the limestone, and their 

 removal brought aboutacollapse, 

 degradation, and settling-down 

 of great parts of the formation. 

 The most obvious result of 

 this proeess is the brecciation 

 and internal deformation which 

 . are such common features of the 

 rock. The less obvious changes 

 are those resulting from the 

 removal of sulphates close!}* in- 

 corporated with the mass of the 

 rock, leading to a molecular 

 degradation with consequent 

 segregation, and other processes 

 which bring about a more or 

 less complete obliteration of the 

 fossils. 



The solution-breccias des- 

 cribed in the present paper 

 frequently simulate effects which 

 might have been anticipated 

 if the Permian rocks had been 

 subjected to horizontally-acting 

 dynamic forces. While not pre- 

 suming to deny the possible 

 m existence of such forces, I have 



seen nothing in the southern part of Durham which would lead me 

 to suppose that the disturbances in the Magnesian Limestone were 

 due to causes other than the effects of solution herein described. 

 The brecciation is confined to the Magnesian Limestone. In 



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