190 ME. C. T. TRECHMAXX OK A MASS OF ANHYDRITE [June I913, 



Some details of the Warren Cement-Works boring were published 

 in connexion with a paper dealing with the salt-beds of South- 

 JEastern Durham, read before the Manchester Geological Society on 

 June 5th, 1888. 1 Mr. Bird remarks upon the abnormal thickness 

 of the anhydrite in this boring, and says : 



' This may probably be the Lower Anhydrite of the Saliferous Beds, although 

 the one foot of limestone above it is rather against the theory.' {Op. cit. p. 575.) 



There seems to be no doubt that the limestone was merely a 

 boulder near the base of the Glacial Clay. 



I was for a long time of the opinion, which seems to have been 

 the opinion of the borers also, that this anhydrite was an abnormal 

 thickening of the Lower Anhydrite Series directly underlying the 

 salt-beds, and supposed that its presence might be explained by 

 the existence of a trough-fault having a north-westerly and 

 south-easterly direction, and bringing that series down against 

 the Upper Magnesian Limestone. 



Several facts, indeed, seemed to favour this view, which it is not 

 necessary to recapitulate here ; and, before the palseontological 

 evidence furnished by the underlying limestones was forthcoming, 

 the probabilities were about equally divided between the fault and 

 the inclusion theories. 



Against the fault theory, the following reasons may be cited, 

 which were kindly suggested to me by Prof. G. A. Lebour: — 



(i) No bed of anhydrite or gypsum approaching a thickness of 265 feet is 

 met with in the Red Beds overlying the Magnesian Limestone in Durham or 

 North Yorkshire. I find that the greatest recorded thickness of the true 

 Lower Anhydrite of the Saliferous Series is 77 feet 6 inches at the West 

 Hartlepool Cement-Works of Messrs. Casebourne ; while in the Seaton-Oarew 

 boring it was only 38 feet 7 inches thick. Taking into account the whole 

 of the anhydrite-beds met with in these two borings : that is, the upper 

 layer which is always met with overlying and protecting the salt, and the 

 lower series of more variable thickness underlying the salt, together with a 

 bed of red marl, presumably representing the salt absent here, the total 

 thickness was 124 feet 6 inches at West Hartlepool and 54 feet 7 inches at 

 Seaton Carew. 



(ii) Among all widely-developed dolomitic rocks abroad, layers or lenticles 

 of gypsum or anhydrite, regular or irregular, and often of very great size and 

 thickness, are common at many horizons, and by their solution and erosion 

 have been repeatedly shown to be the cause of much internal deformation of 

 the enclosing limestone, as well as of many ' slacks ' and valleys at the surface. 

 The phenomenon is very usual in connexion with the Trias in many parts of 

 the Alps, where it has been called in to explain the features of certain high- 

 level lakelets and valleys. So far as physical and chemical characteristics 

 are concerned, the Triassic Alpine Dolomites are in many ways comparable 

 with the Durham Permian Magnesian Limestones. 



However, the presence of two genera of brachiopoda in the lime- 

 stone underlying the anhydrite at Hartlepool must allocate it to 

 some bed of the great middle fossiliferous division of the Magnesian 



^ W. J. Bird, Trans. Manchester Geol. Soc. vol. xix (1888) p. 564. 



