MAGNESIAN'-LIMESTONP; OF THE COUNTY OF DURnAM. 65 



the bed, it seems safe to conclude that the method of formation 

 of these globes or balls is more stalactitic, using that word in a 

 primary sense, than geologists and others seem willing to admit. 



But that these modifications of structure are secondary and 

 superinduced, and are not the original form or material which 

 was first deposited, even the most superficial observer will be 

 inclined to admit, when it is pointed out that these beds were 

 at first deposited in finely laminated layers of yellow, powdery, 

 dolomitic marl, and that between some of these layers organic 

 remains were entombed, which have not been entirely obliter- 

 ated, but are still preserved in some of the beds, which are 

 now almost entirely filled with more or less crystalline compact 

 globes or partially radiated spheres. 



It may be of interest to state that, according to the analyses 

 made many years since by Messrs. Browell and Kirkby,* the 

 concretionary beds contain a large percentage of carbonate of 

 lime, and scarcely a ti'ace of magnesia. On the contrary, the 

 yellow, soft, marly beds are composed of nearly equal parts 

 of carbonate of lime and carbonate of magnesia, sometimes the 

 latter in excess of the former. In former times the fine, yellow, 

 laminated limestone was extensively quarried in Marsden Bay, 

 and conveyed to the Jarrow Chemical "Works for the manufacture 

 of Epsom Salts, which is an additional proof of the large per- 

 centage of magnesia contained in some of the originally-deposited 

 and unaltered beds. That this stratum is original and unaltered 

 is proved by the perfect manner in which the remains of small 

 fishes occasionally found in it are preserved. 



* See Nat. Hist. Trans. Northumberland, Durham, and Newcastle-upon-Tyne, Vol. I., 

 pp. 204—230, 1867. Refer also to Prof. Sedgwick's Memoir, Trans. Geol. Soc, Ser. II., 

 Vol. III., 4to. 



