Limestone, etc. 



i 



232 ME. C. T. TEECHMANN ON THE LITHOLOGT [June 1914, 



9. On the Lithologt and Composition o^Dfeham Magnesian 

 Limestones. By Chaeles Tatloe Teechmann, B.Sc, 

 F.G.S. (Read February 4th, 1914.) 



[Plates XXXVI & XXXVII— Microscope-Slides.] 



Contents. 



Page 



I. Introduction 232 



II. Lithology and Composition 235 



f South Durham Salt-Deposits. 

 Highest Limestones (Hartlepool and 

 (1) Upper Magnesian J Eoker Series). 



Upper Limestones with Chondrites. 

 Concretionary Beds. 

 Flexible Limestones and Similar Beds. 

 Upper Shell-Limestones. 

 Calcareous Shell-Limestones. 

 Lower Shell-Limestones. 

 Sulphate-bearing Magnesian Limestones. 

 Limestone. ^ Bedded Series, on the Eastern side of the 



Shell-Limestone. 

 Bedded Series, on the "Western side of the 



Shell-Limestone. 

 Lower Limestones (Calcareous & Dolo- 

 mitic). 

 _ Marl Slates. 



III. Evidence bearing upon Dolomitic Deposition and on the Dolomiti- 



zation of the Shell-Limestone 249 



IV. Segregation and Dedolomitization 251 



V. The Origin of the Cellular Structures 256 



VI. The Insoluble Residues 257 



VII. Summary of the General Conditions of Deposition 259 



Vin. Synopsis of the Main Constituents of Durham Magnesian 



Limestones 261 



(2) Middle Magnesian 



(3) Lower Magnesian ^ 

 Limestone, etc. 



I. Inteoduction. 



The analyses of which a selection is here presented were com- 

 menced during an investigation of the Magnesian Limestones of 

 the southern part of the Durham area. The results proved of 

 sufficient interest to induce me to extend the enquiry over a con- 

 siderable variety of rocks included in the whole Permian area of 

 Durham. 



The work was undertaken, primarily in order to obtain satisfac- 

 tory and reliable information regarding the following questions : — 



(1) The quantity and nature of the insoluble residues in the rock ; 



(2) The amount of iron, together with the traces of alumina and phosphoric 



acid accompanying it, and the state of oxidation of the former ; 



(3) The dolomitic or non-dolomitic character of the various beds ; and 



(4) The possibility of sulphates still remaining in the rock. 



