52 CELLULAR MAGNESIAN LIMESTONE OF DURHAM. [Feb. I903, 



the mineral matter formed into a concretion instead. He thought 

 that this would, in a measure, account for the Author's specimens 

 from Sunderland; but how all these varied forms of pseudo- 

 crystalline bodies came about was a puzzle still, and the right 

 persons to solve it were chemists and mineralogists. 



Mr. A. P. Young remarked that, in trying to explain these 

 structures, we were not bound to confine our attention to the present 

 chemical constituents of the rock. The possible removal of gypsum 

 and soluble salts so frequently associated with dolomite in the 

 Zechstein formation must be taken into consideration. Instances 

 were furnished by the Stassfurt beds and the Eauchwacke. Some of 

 the Author's specimens showed druses which recalled similar cavities 

 in the Eauchwacke containing the so-called ' asche,' a powder 

 consisting chiefly of dolomite and calcium-sulphate. 



Prof. Garwood congratulated the Author on the splendid series of 

 photographs and specimens which he had exhibited and described. 

 But he confessed that he had been disappointed in the slight allusions 

 made to the mode of formation, among which he could not discover 

 anything that was new, or that was contrary to what he, the speaker, 

 had set forth in a paper in the 'Geological Magazine' for 1891, 

 p. 433. He thought that the cause of the origin of the concretions was 

 as obscure as of yore, and that the best that we could do at present 

 was to put them down as 'organized accidents.' With regard to 

 the suggestion of one of the speakers that a bulk-analysis should be 

 made of the beds containing concretions and the non-concretionary 

 beds interstratified with them, he would like to point out that he 

 had made and published such analyses in the paper already men- 

 tioned, and that his results showed a remarkable correspondence in 

 the percentage of magnesium-carbonate in the two beds, the 

 relative amount of magnesium to calcium-carbonate in the one 

 case being 40 to every 100 parts, and in the other 43. For fuller 

 details he would refer the Author to the paper which he had quoted. 



The Author expressed his thanks for the reception accorded to 

 his paper. 



